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Title: Hygiene: a manual of personal and public health (New Edition)
Author: Newsholme, Sir Arthur
Language: English
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Transcriber’s Notes

Obvious typographical errors have been silently corrected. Variations
in hyphenation have been standardised but all other spelling and
punctuation remains unchanged.

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superscripts thus y^{en}.

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                              _A MANUAL_


                      Personal and Public Health


               ARTHUR NEWSHOLME, M.D., F.R.C.P., LOND.,

                             OF HEALTH.

                   NEW EDITION, 1902.  ILLUSTRATED.




The writing of a preface is perhaps superfluous for a book which
has had a large and steady sale for nearly twenty years, and which
has evidently met with the approval of a large constituency. A few
words of introduction appear, however, desirable in view of the facts
that the present edition has been almost entirely re-written; that a
large amount of new matter has been introduced; and that, so far as
is known, the comments on each subject represent the most recent and
authoritative knowledge upon it.

An attempt has been made to meet the requirements of medical students,
as well as of science students and general readers, for whom former
editions were chiefly intended. A large class of medical students and
practitioners do not require the detailed statement of the subject
contained in the larger text-books. For them, and, it is hoped, also
for a large number of candidates for diplomas in public health and
in sanitary science, the present edition will prove to be useful. At
the same time, the subject has been treated as non-technically as
is consistent with accuracy, in order to retain its suitability for
non-medical readers. A large number of new illustrations have been

The new chapters dealing with Dietetics, Trade Nuisances,
Meteorological Observations, Tuberculosis, Disinfection, and Vital
Statistics will, it is believed, enhance the value of the book.

Attention is also drawn to the solutions of mathematical problems in
the different branches of hygiene, of which a table of contents is
given on page viii.

In its new form, it is hoped that this work will be found to have
retained its value as a plain and straightforward account of its
subject for the general public and for science students; and to
have become a practical guide to sanitary inspectors and to medical
students, whether preparing for a diploma in public health, or studying
hygiene as an important branch of medicine. The use of smaller type for
specially technical matter of less general interest will facilitate
discriminative reading.


  _February 28th, 1902_.


  CHAPTER.                                     PAGE

  I.—INTRODUCTORY                                                      1

  II.—FOOD                                                             4

  III.—THE VARIETIES OF FOOD                                           9

  IV.—DISEASES DUE TO FOOD                                            23

  V.—DIET                                                             29


  VII.—CONDIMENTS AND BEVERAGES                                       45

  VIII.—FERMENTED DRINKS                                              55

  IX.—WATER                                                           65

  X.—THE STORAGE AND DELIVERY OF WATER                                74

  XI.—IMPURITIES OF WATER                                             78


  XIII.—THE PURIFICATION OF WATER                                     94

  XIV.—COMPOSITION AND PROPERTIES OF AIR                             100

  XV.—SUSPENDED IMPURITIES OF AIR                                    105

  XVI.—GASEOUS AND OTHER IMPURITIES OF AIR                           111

  XVII.—TRADE NUISANCES                                              120

  XVIII.—THE EXAMINATION OF AIR                                      125

  XIX.—THE PURIFICATION OF AIR                                       129

  XX.—GENERAL PRINCIPLES OF VENTILATION                              132

  XXI.—PROBLEMS AS TO VENTILATION                                    137

  XXII.—METHODS OF VENTILATION                                       146


  XXIV.—THE WARMING OF HOUSES                                        158

  XXV.—HOUSE DRAINAGE                                                165

  XXVI.—CESSPOOLS AND MAIN SEWERS                                    183

  XXVII.—PROBLEMS AS TO FLOW IN SEWERS                               187

  XXVIII.—THE DISPOSAL OF SEWAGE                                     190

  XXIX.—CONSERVANCY METHODS                                          194

  XXX.—POSITION OF THE HOUSE                                         201


  XXXII.—CONSTRUCTION OF THE HOUSE                                   209

  XXXIII.—THE SOIL                                                   219

  XXXIV.—CLIMATE AND WEATHER                                         227

  XXXV.—METEOROLOGICAL OBSERVATIONS                                  237

  XXXVI.—PERSONAL HYGIENE                                            245

  XXXVII.—PERSONAL HYGIENE—EXERCISE                                  249

  XXXVIII.—PERSONAL HYGIENE—REST AND SLEEP                           257

  XXXIX.—PERSONAL HYGIENE—CLEANLINESS                                260

  XL.—CLOTHING                                                       265

  XLI.—PARASITES                                                     273


  XLIII.—INFECTIVE DISEASES                                          284

  XLIV.—ACUTE INFECTIVE DISEASES                                     291

  XLV.—TUBERCULOSIS                                                  309

  XLVI.—NOTIFICATION AND ISOLATION                                   317

  XLVII.—DISINFECTION                                                324

  XLVIII.—VITAL STATISTICS                                           335




     „     „  DIETETICS                 35

     „     „  WATER ANALYSIS            86

     „     „  AIR ANALYSIS             126

     „     AS TO VENTILATION           137

     „       „   FLOW IN SEWERS        187

     „     IN METEOROLOGY              242

     „     AS TO WORK                  254

     „     IN VITAL STATISTICS         336




In classical mythology, Æsculapius was worshipped as the god of
Medicine, while his daughter Hygeia had homage done to her as the sweet
and smiling goddess of Health. The temples of these two deities were
always placed in close contiguity; and statues representing Hygeia
were often placed in the temple of Æsculapius. In these statues she is
represented as a beautiful maid, holding in her hand a bowl, from which
a serpent is drinking—the serpent typifying the art of medicine, then
merely an art, now establishing its right more and more to the dignity
of a science.

That considerable attention was paid in very early times to matters
relating to health, is also shewn by the elaborate directions contained
in the Mosaic law as to extreme care in the choice of wholesome foods
and drinks, in isolation of the sick, and attention to personal and
public cleanliness. It is not surprising, therefore, to find that the
Jews, throughout the whole of their history, have apparently enjoyed a
high standard of health.

In this country great ignorance of the laws of Health has prior to
the last fifty years prevailed, and consequently preventible diseases
have been rampant, and have claimed innumerable victims. Each
century has been marked by great epidemics, which have swept through
the country, scattering disease and death in their course. In the
fourteenth century, for instance, there was the Black Death, a disease
so fatal that it left scarcely one-fourth part of the people alive;
while Europe altogether is supposed to have lost about 40 millions
of its inhabitants, and China alone 13 millions. A century and a
half later came the Sweating Sickness (though there were a score of
minor epidemics in between). This was carried by Henry the Seventh’s
army throughout the country, and so great was the mortality, that
“if half the population in any town escaped, it was thought great
favour.” Considerable light is thrown on the rapid spread of this
disease after its importation, when we remember that there were no
means of ventilation in the houses; that the floors were covered with
rushes which were constantly put on fresh without removing the old,
thus concealing a mass of filth and exhaling a noisome vapour; while
clothing was immoderately warm and seldom changed; baths were very
seldom indulged in, and soap hardly used.

In the sixteenth and seventeenth centuries there were five or six
epidemics of The Plague, and it was only eradicated from London, when
all the houses from Temple Bar to the Tower were burned down in the
Great Fire of September 2nd, 1666, which destroyed the insanitary and
necessitated the building of new and larger houses.

Scurvy, jail-fever, and small-pox, are other diseases which were
formerly frightfully prevalent. Jail-fever, the same disease as the
modern typhus-fever, has now become practically extinct in its former
habitat, owing largely to the noble work of John Howard, “whose life
was finally brought to an end by the fever, against the ravages of
which his life had been expended.” This disease was fostered by
overcrowding, ill-ventilation, and filth.

Scurvy formerly produced a very great mortality, especially among
sea-faring men. In Admiral Anson’s fleet in 1742, out of 961 men, 626
died in nine months, or nearly two out of every three, and this was no
solitary case. Captain Cook, on the other hand, conducted an expedition
round the world, consisting of 118 men; and although absent over three
years, only lost one life. He was practically the first to demonstrate
the potency of fresh vegetables in preventing scurvy.

The striking facts respecting small-pox will be found on page 293. The
general death-rate has also greatly declined. Thus while the annual
death-rate in London 200 years ago was 80 per 1,000, it only averaged
18.8 in the four years 1896-99; and the death-rate of England and Wales
has declined from 22.4 in 1841-50 to 18.7 per 1,000 in 1891-95 and 17.6
in 1896-99.

That much still remains to be done is evident on every hand. There is
little doubt that the general death-rate might be reduced to 15 per
1,000 per annum, instead of the present 18, were the laws of health
applied in every household and community. It has been estimated that
on the average at least 20 cases of sickness occur for every death;
therefore nearly half of the population is ill at least once a year.
A simple calculation will show how much loss the community annually
suffers from this vast mass of preventible sickness. It amounts to
many millions of pounds, leaving out of the reckoning the suffering
and distress which are always associated with sickness. For details
relating to special diseases, see page 297.

In the prevention of this mass of sickness, the knowledge of its
causation is half the battle; when once a disease is traced to its
source, as a rule, the agency which produces it can be avoided.

The reason why even more progress has not been made in the prevention
of disease is not far to seek. In order to prevent a disease it is
necessary to remove its causes. The causes of disease can only be
ascertained by a careful investigation of its phenomena; and it is
only within the last century that these have been studied to any
large extent scientifically. Such knowledge of morbid processes not
only results in improved measures of treatment, but in more rational
and complete measures of prevention. Thus, not only is the number of
diseases which are _curable_ becoming gradually augmented, but the
number _preventible_ is even more rapidly on the increase.

Inasmuch as the preservation of health involves the prevention
of disease, Hygiene, the science of health, is sometimes called
_Preventive Medicine_.

The subject of Hygiene naturally divides itself into two parts, the
health of the individual, and that of the community, or _Personal and
Public Health_.

The former treats of the influence of habits, cleanliness, exercise,
clothing, and food on health; while the latter is concerned with the
interests of the community at large, as affected by a pure supply of
air and water, the removal of all excreta, the condition of the soil,
and with the administrative measures required to secure the removal
of evil conditions. It is obvious, however, that these two divisions
are not mutually exclusive. What is important to the health of the
community, is equally so to each individual member of it. The purity of
air and water, for instance, is of immense importance both personally
and collectively.

It will be convenient to study first the three main factors in relation
to health—food, water, and air—subsequently considering other matters
of importance to health (see pages 4-157).



PHYSIOLOGICAL CONSIDERATIONS.—All substances are foods which, after
undergoing preparatory changes in the digestive organs (rendering them
capable of absorption into the circulation), serve to renew the organs
of the body, and maintain their functions. Foods have been classified
as _tissue producers_ or _energy producers_, the first class renewing
the composition of the organs of the body, and the second class
supplying the combustible material, the oxidation (or more correctly
the _metabolism_) of which is the source of the energy manifested in
the body. The two main manifestations of energy in the body are heat
and mechanical motion, which are to a large extent interchangeable.

All foods come under one of these heads; they are either tissue or
energy producers. They may be both, and in many cases are so. Thus,
all nitrogenous foods (as meat, legumens, etc.) not only help to form
the nitrogenous tissues of the body, but their largest share becomes
split up into fats and urea, and so forms a source of heat to the
body. Similarly fats may possibly, after assimilation, enter into
the composition of the various tissues containing fat (of which the
brain is the most important), though they usually supply an immediate
source of heat. Proteid foods are, however, the tissue producers _par
excellence_, other foods serving as the immediate sources of energy
when metabolised in the body.

Certain foods do not directly serve either as tissue or energy
producers, but are useful in aiding the assimilation of food. Such are
the various condiments which may be classed as adjuncts to food. Salt
is so necessary to the assimilation of food and to the composition
of the various tissues, that it may be ranked as an important food.
Water, again, though already oxidised, and so not an immediate source
of energy, is absolutely necessary to the assimilation of food, to
the interchange between the various tissues and the blood, and to the
elimination of effete products.

CLASSIFICATION OF FOODS.—Inasmuch as milk supplies all the food
necessary for health and growth during the first year of life, it may
reasonably be expected to afford some guidance as to the necessary
constituents of a diet for the adult; although the conditions of life
being altered in the latter, we can hardly expect the same proportions
of the different materials to hold good. In the infant rapid growth
and building up of new tissues and organs are going on, involving the
necessity for a larger proportional amount of nitrogenous food than in
the adult.

The following is the average composition of 100 parts of

  │                │ HUMAN MILK. │ COW’S MILK. │
  │_Casein_        │     2.4     │     4.0     │
  │_Albumin_       │      .6     │      .9     │
  │_Fat_           │     2.9     │     3.5     │
  │_Sugar_         │     5.9     │     4.0     │
  │_Salts_         │      .16    │      .7     │
  │                │    ────     │    ────     │
  │ _Total Solids_ │    11.96    │    13.1     │
  │ _Water_        │    88.04    │    86.9     │

It is evident from this analysis of milk that our food must contain (at
least) representatives of all the above divisions. We have, therefore:—

  1. =Nitrogenous Foods.=
  2. =Hydrocarbons or Fats.=
  3. =Carbohydrates or Amyloids.=
  4. =Salts.=
  5. =Water.=

Condiments and stimulants (tea, coffee, alcohol) are not foods in the
strict sense of the word, and will be discussed in a later chapter.

=Nitrogenous Foods= include albumin, casein, gluten, legumen, fibrin,
and gelatin. They all agree in consisting of a complex molecule
containing many atoms of carbon, hydrogen, oxygen, and nitrogen, with
the addition of smaller quantities of sulphur, and in some cases
phosphorus. The nitrogenous substances used as food may be divided into
two groups, (_a_) those containing gelatin, and (_b_) numerous bodies
which receive the common name of proteids or albuminoids.

The percentage composition of gelatin is:—

  │   50.0    │    6.6    │   18.3    │   25.1    │

The percentage composition of all proteids lies within the following

  │   52.7 to │    6.9 to │   15.4 to │   20.9 to │    0.8 to │
  │   54.5    │    7.3    │   16.5    │   23.5    │    1.6    │

Proteids also contain a small amount of phosphorus, chiefly as
phosphate of lime, but also in minute quantity in their essential
structure. Various proteids are used in food, _e.g._ serum-albumin in
the blood and tissues of animals; egg-albumin in the white of eggs;
myosin in flesh; casein in milk; legumin, or plant-casein, in the seeds
of leguminous plants; gluten in wheat-flour, etc.

Proteid foods are pre-eminently important, as they construct and keep
in repair the tissues of the body. They are not used solely for this
purpose. A large share of the energy of the body is derived from the
metabolism of proteids. The amount required for these purposes will be
discussed on page 32. Meanwhile, it may be said that it is not found
to be compatible with efficient health simply to supply an amount of
proteid food which will suffice to replace the wear and tear of the
tissues, leaving fats and carbohydrates to supply the energy of the
body. Deficiency of proteid food always leads to ill-health; and it
would appear that in all cases proteid food determines, to a large
extent, the metabolism of non-nitrogenous food, and so is favourable
to all vital action. The action of nitrogenous food in thus increasing
metabolism may make it, when in _relative excess_, a tissue waster.
Banting’s cure for corpulence is founded on this principle, lean meat
alone being taken, all starchy and saccharine foods being carefully

By _metabolism_ is meant the changes undergone by food before it
reaches the state in which it is finally eliminated from the body.
It is commonly spoken of as _oxidation_, but this word less exactly
represents the facts. The complexity of the changes undergone by food
in the body may be better appreciated by a glance at the following
schematic statement, which only gives an approximation to the truth:-

     ALBUMINOID.         (STEARIN).          STARCH.     GRAPE-SUGAR.
   C₇₂H₁₁₂N₁₈SO₂₂.     C₃H₅(C₁₈H₃₅O₂)₃.     _x_(C₆H₁₀O₅).   (C₆H₁₂O₆).
          Various intermediate products, which are finally broken down
                             into and eliminated as
                 │                    │                    │
          Urea, CH₄N₂O.      Carbonic acid, CO₂.    Water, H₂O.

=Hydrocarbons=, or fats, consist of three elements, carbon, hydrogen,
and oxygen, the amount of oxygen present not being sufficient to
oxidise completely either the hydrogen or the carbon. Thus the molecule
of stearin, which may be taken as a typical fat, has the formula C₃H₅

In respect to their comparatively unoxidised condition fats compare
favourably with starch and sugar, C₆H_{10}O₅ and C₆H_{12}O₆
respectively. It is evident that in starch the H_{10}O₅ = 5H₂O, and
that in sugar H_{12}O₆ = 6H₂O, so that in both cases only carbon
remains uncombined with oxygen. Dried fats produce by their oxidation
2¼ times as much heat as a corresponding amount of sugar or starch;
but the relative advantage of fat is not quite so great as would appear
from this comparison, inasmuch as metabolism within the body is not
identical with oxidation.

The fat obtained from food is not simply deposited in the body as such,
to form a store of combustible matter, and to fill up the interstices
between the different tissues. If this were so, the kind of fat
deposited would vary with the food, which is not the case. The fat of
the body is probably not formed directly from fatty food, but as the
result of the metabolism of nitrogenous foods when this metabolism is
incomplete. In the formation of milk this can be distinctly proved: the
fat cells are formed from the protoplasm of the cells of the mammary

Possibly carbohydrate food may be a source of fat, as well as
nitrogenous and fatty food. This appears to be the case in the
Strasburg goose, which is kept penned up in a warm room, and fed
entirely on barley-meal, in order to produce an enormous fatty liver
for the delicacy termed _pâté de foie gras_. But it may be that the
large accumulation of fat in the liver is due to the warmth and
inaction of the goose diminishing metabolism, and producing a fatty
degeneration of the nitrogenous material of the liver.

Fats and carbohydrates, unlike proteids, do not excite metabolism in
the system, and so, if in excess of the requirements of the system,
can be stored up with comparative ease. Quiet and warmth, diminishing
metabolism, conduce to the accumulation of fat in animals being fed for
the market; and the same applies to human beings.

=Carbohydrates or amyloids= include the various starchy and saccharine
foods. They are inferior to fats in nutritive power, but, being very
digestible, are in much greater favour. In the process of digestion,
starch is converted into grape sugar, and starch and sugar are
practically equal in nutritive power.

Even when carbohydrates are entirely absent from the food, they may be
produced in the organism by the breaking up of nitrogenous matter. This
certainly happens in diabetes, in which the nitrogenous food rapidly
becomes converted into sugar and urea.

The deprivation of carbohydrate food is much better borne than that of
fats, because in the latter the hydrogen is not completely oxidized,
and because fats aid the assimilation of other food.

=Salts=, and especially common salt (chloride of sodium), are essential
to health. An average adult human body contains about seven pounds of
mineral matter, of which about five-sixths is in the bones. On analysis
the whole body yields about five per cent. of ash.

Chloride of sodium is necessary for the production of the acid
(hydrochloric) of gastric juice, and of the salts of bile; half the
weight of the ash of blood consists of it. An adult requires 150 to 200
grains of salt per day; a large part of this is taken in meat, bread,
etc.; and but little need be taken as a condiment. Potassium salts form
an important part of milk, muscle juice, and the blood corpuscles.
They are obtained from bread and fresh vegetables and fruits. It has
been maintained that deficiency of potassium salts causes scurvy (see
page 28); but this is now discredited, and probably potash is chiefly
useful because of the vegetable acids with which it is associated
in fruits and vegetables, which when oxidised, help to maintain the
alkalinity of the blood, _e.g._, tartrates, citrates, and malates,
which become carbonates in the circulation. Calcium phosphate (bone
earth) is essential for the growth of bones, and is very important
for the young. The best source for it is milk. There is more lime in a
pint of milk than in a pint of lime water. Next to milk, come eggs, and
then cereals, especially rice as a source of calcium. Lime salts and
phosphates as drugs do not benefit like the same substances taken in
natural food, and rickets is not curable by taking such drugs.

Oxide of iron is always present in the ash of blood and muscles, and
in smaller quantities in milk. Fish and veal are usually deficient in
it, while beef and yolk of egg are foods richest in iron. The amount of
iron required in food is minute, and it is amply supplied by ordinary

Phosphorus is an essential building material for the body. It is
contained in foods chiefly in organic combination. The foods richest in
it are yolk of egg, sweetbread (thymus), fish-roe, calves’ brains, and
the germ of wheat. Milk and cheese are very rich in phosphates.

=Water= forms an important article of diet. This is evident from the
fact that 80 per cent. of the blood consists of it, and 75 per cent. of
the solid tissues; and from the fact that the daily loss of water from
the system averages 50 ounces (2½ pints) by the kidneys, and about
40 ounces by the skin and lungs. Water is not simply received into
the system as a liquid. It forms a large proportion of the solid food
taken. Thus, 87 per cent. of milk, 78 per cent. of fish, 72 per cent.
of lean meat, 38 per cent. of bread, 13 per cent. of peas, and 92 per
cent. of cabbage, consist of water.

Solid food is dissolved in the alimentary canal by the watery
secretions derived from the blood. Water swallowed as food, begins to
pass on into the intestine at once. The statement that free consumption
of water at meals delays digestion by diluting the gastric juice is
therefore not well grounded. In the blood, water serves to carry
nutrient materials to all the tissues; and, at the same time being
circulated all over the system, equalises the temperature, favours
chemical changes, and washes all the tissues. By water again, the
effete matters which have been separated by the kidneys are washed out
of its tubes.

The =Oxygen= of the air, in a broad sense, forms one of the foods of
the system. This will be considered later.

Besides the above classification, foods have also been classified as

  1. _Inorganic food_—Oxygen, salts.

                      {Animal       {Nitrogenous.
                      {             {Non-nitrogenous.
  2. _Organic foods_  {
                      {Vegetable    {Nitrogenous.
                      {             {Non-nitrogenous.

Or, as—

                      {Animal       {Nitrogenous.
                      {             {Non-nitrogenous.
  1. _Solid foods_    {
                      {Vegetable    {Nitrogenous.
                      {             {Non-nitrogenous.

  2. _Liquid foods_   {Milk and its products.
                      {Tea and similar beverages.
                      {Alcoholic beverages.

  3. _Gaseous foods_—Air.



NITROGENOUS ANIMAL FOODS.—These are divided into two groups, the
one containing gelatin, and the other all the proteid or albuminoid
substances, which are taken in the flesh of various animals, and in
milk and eggs.

=Gelatin= is obtainable from bones, and from connective tissue wherever
found. Being easily digested, and absorbed, it has been very popular as
an invalid’s food; but the fact that animals cannot sustain life on it
without the addition of proteids proves that its value is limited. It
is incapable of building tissues, but is a valuable _proteid-saver_,
being able to save from metabolism half its weight of proteid, or twice
as much as is spared by an equal weight of carbohydrate. Its utility
in this direction is, however, limited, because of the dilute form in
which it is taken in ordinary foods. It is useful for invalids, partly
because it forms a bulk, and prevents the evil tendency to give their
food in too concentrated a form; partly because it forms a source of
easily metabolised material, and so prevents tissue-waste; and partly
because it commonly contains phosphate of lime, derived from the bones
forming the source of gelatin.

Gelatin as prepared for the table contains a considerable proportion of
water; as little as one per cent. of gelatin in water will cause it to
gelatinise on cooling. Isinglass obtained from the floating bladder of
the sturgeon is an example of the purest kind of gelatin; glue is an
inferior sort, made from bones, etc.

Gelatin is only a cheap food when obtained, for instance, from bones
which cannot otherwise be utilised. When made from veal it is costly
out of proportion to its dietetic value.

The =Flesh= of various animals is one of the main sources of our
nitrogenous and fatty food. Meats may be divided into two kinds, viz.,
=red meat= and =white meat=. These gradually merge into one another. As
common examples of red meats, we have beef, mutton, pork, game, wild
fowl, and salmon.

The common fowl and turkey, most fishes, rabbits, crustaceans, and
molluscs, are examples of white meat. As a rule white meats are more
digestible than red, having more delicate fibres, and containing a
smaller proportion of nitrogenous matter.

Flesh consists almost entirely of muscular tissue, of which there are
two kinds, striped and unstriped.

The striped is the variety most commonly used as food. Unstriped muscle
has a softer texture, but is not so easily masticated as striped,
and for this reason may be indigestible. _Tripe_ is composed of the
unstriped muscle and connective tissue of the stomach of the cow, and
if well cooked forms a cheap and easily digested dish.

_The influence of feeding_ on the quality of the meat is great. In
ill-fed or old animals, connective tissue is more abundant, and the
meat is tougher. Well-fed and fattened meat contains for equal weights
much more nutritious matter than non-fattened meat, the fat which is
deposited in the muscle replacing water and not proteid. Hence the
gain in nutritive value is an absolute one, and is not attained at the
expense of the proteid part of the meat. Young animals, again, contain
more water and fat and a larger proportion of connective tissue than
the full-grown, and are consequently not so nourishing.

Meat ought to be eaten either before the onset of _rigor mortis_, or
near its end, before putrefaction has commenced. During _rigor mortis_
it is denser, tougher, and more difficult to digest than after it.

The proportion of fat in meat varies greatly in different individuals
of the same species, in different animals, and in different parts of
the same animal. According to Dr. Ed. Smith, the proportion of fat in
fat oxen is ⅓, in fat sheep ½, in calves ⅙, lambs ⅓, and fat
pigs ½.

Good meat, whether beef or mutton, ought to have a marbled appearance,
a medium colour, neither pale pink nor deep purple; its texture should
be firm, and not leave the impress of the finger; its odour slight and
pleasant, the juice reddish and acid, the bundles of fibres not coarse,
and free from foreign particles imbedded in them; and lastly, it should
not be taken from an animal killed near the time of parturition, nor in
consequence of any accident or disease.

=Beef= is, as a rule, more lean than mutton or pork; it has a closer
texture, and more nutritive material in a given bulk. It is also
fullest of the red-blood juices, and possesses a richer flavour than
the two others.

Liebig’s beef extract contains little if any albumin or gelatin. It
is a useful stimulant to the gastric secretion, as in soups at the
beginning of a meal, but is not a food. Its chief constituents are the
various extractives of meat, the most important of which are inosinic
acid, kreatin (C₄H₉N₃O₂,H₂O), and inosite, or muscle sugar (C₆H_{12}O₆,
2H₂O). Even in substances like Bovril, containing powdered meat fibre
mixed with Liebig’s extract, the amount of nutritive material is very
small. The white of one egg contains as much nutritive matter as three
teaspoonsful of bovril. None of these substances can be trusted like
eggs or milk to keep a patient alive for several weeks.

=Mutton= is regarded as being more suitable for people of sedentary
occupation than beef. =Lamb= is more watery than mutton, and less

=Veal=, as ordinarily prepared in this country, is difficult of
digestion; its shreddy, juiceless fibres eluding the teeth, and
consequently not undergoing proper mastication.

=Pork= is not so digestible as beef or mutton, partly because of the
large proportion of fat, and partly because its fibres are hard and
difficult to masticate. Its digestibility varies greatly with its age,
breeding, and proportion of fat.

The =Flesh of Birds= contains very little fat, and that found separate
from the meat is rarely nice. Most birds are edible, but fish-eating
birds are apt to be nasty. As a rule, the flavour of the male bird is
richer than that of the female. The chief virtues in poultry are their
tenderness, and the large proportion of phosphates they contain. They
are deficient in fat and in iron. To compensate for the former, one
commonly takes with them melted butter and fat bacon or pork sausages;
to compensate for the latter, the addition of Liebig’s extract to the
gravy is useful. Young, and consequently tender, birds are known by
their large feet and leg-joints. When a bird appears at table with
violet-tinged thighs and a thin neck, if possible avoid being helped to
the leg. Wild fowls are harder and less digestible than tame. In ducks
and geese fat is more abundant, and of a stronger flavour; they are,
consequently, not so digestible as fowls.

=Fish= forms an important article of diet. It is easily cooked, and
usually very digestible; it possesses a larger bulk in proportion
to its nutritive quality, and hence is very valuable for those who
habitually take an excess of meat food, which is commonly the case with
those leading sedentary lives, and in declining years. There appears
to be no foundation for the statement that fish is rich in phosphorus,
and is thus a good brain food. Generally, white-fleshed fish is more
digestible than red-fleshed (such as salmon), the latter usually
containing more fat than the former. When the fat is distributed
throughout the flesh, as in the salmon, fish is more satisfying than
when it is mainly stored up in the liver, as in the cod-fish. According
to Payen, the percentage proportion of fat in soles is only 0.248,
in whiting 0.383, conger eel 5.021, mackerel 5.758, eels 23.861. The
addition of some fatty food, as melted butter, is very advisable to
such meats as poultry, rabbits, soles, whiting, plaice, haddock, cod,
turbot, and other fishes; whereas sprats, eels,. herrings, pilchards,
salmon, etc., are more or less rich in fat.

=A Hen’s Egg= usually weighs a little under two ounces. It consists of
74 per cent. of water and 26 per cent. of solid matter. The white of
the egg is chiefly albumin, the yolk consists of a very digestible oil,
rich in phosphorus and iron, each particle of the oil being enveloped
in a form of albumin called vitellin. The salts are chiefly contained
in the shell. There is no sugar in the egg, the necessity for such
oxidisable material for the chick being obviated by the heat produced
by incubation. Eggs, when kept for some time, lose weight, owing to
evaporation through the porous shell; similarly, air entering from
without sets up decomposition. In a solution of brine containing an
ounce of common salt to half a pint of water, fresh eggs sink, stale
ones float; rotten eggs may even float in fresh water. Eggs may be
preserved by keeping them in brine, or, better still in lime water, or
by smearing them over with lard or butter, as soon as possible after
they are laid.

=Cow’s Milk= has a specific gravity of 1028-34, and on allowing it
to stand in a long narrow vessel ought to form ten or twelve per
cent. of its volume of cream. The percentage composition of human
and cow’s milk has been given on page 5. The legal minimum standard
for dairy milk, which is presumably derived from a number of cows,
is now 3 per cent. of fat, and 8.5 per cent. of “solids not fat.”
This standard is unfortunately very low, and allows a considerable
margin of adulteration, which cannot be prevented by legal means. Thus
ordinary milk derived from a herd of cows would probably contain 4.5
per cent. of fat; and it is, therefore, practicable to mix pure new
milk with a large proportion of separated milk, and yet keep within
the legal standard. This is largely done in towns, and infants suffer
much from the deficiency of cream in their sole food (see page 28). The
lactometer determines the specific gravity, which should be taken at
a temperature of 60° F. In skimmed or separated milk it will be over
1034; watering on the contrary lowers the specific gravity. If the milk
has been both watered and skimmed the specific gravity will give an
uncertain indication. Measurement of the cream in a tall narrow glass
will enable one to detect the second possible source of fallacy; but
the composition of milk can only be certainly determined by analysis.
This is done (_a_) by evaporating a weighed amount of milk to dryness
and then re-weighing. (_b_) From a separate amount of dried milk the
fat is extracted by ether, the ether then evaporated, the remaining fat
weighed, and its percentage calculated. The weight of fat deducted from
the total solids i.e. (_b_) from (_a_), gives the “solids not fat.” The
following example will make the method then followed clear. The sample
gives 7.9 per cent. of “solids not fat.” Genuine milk contains at least
8.5 per cent. of “solids not fat.”

Then the sample contains—

  100 × 7.9∕8.5  = 92.9 per cent. of genuine milk,

  _i.e._ 7.1 per cent. of water has been added to it.

Half a pint of milk supplies as much nitrogenous nutriment as two
good-sized eggs, and as three and a half ounces of beef. Milk may be
deteriorated (1) by skimming or “separating” by machinery, or (2) by
the addition of water—the first diminishing the proportion of fats, and
the second the total amount of solids.

=Skim Milk= still contains nearly 1 per cent. of fat, but =Separated
Milk=, in which the cream has been removed by centrifugal apparatus,
contains less than 1∕8 per cent.

Skim or separated milk forms a cheap source of nitrogenous food; but
when it is sold mixed with new or alone as new milk, the public is
defrauded, and infants fed on it are robbed of the fat which is so
essential for their growth.

=Condensed Milk= is milk deprived of a large part of its water. It
represents three times its volume of fresh milk. There are in the
market (=a=) unsweetened and condensed whole milk, (=b=) sweetened
and condensed whole milk, and (=c=) sweetened and condensed skim or
separated milk. Unfortunately the latter is most largely sold because
cheapest; and infants are thus often robbed of fat, a most important
element in their food. Always examine the label of each tin carefully,
to ascertain whether the milk has been deprived of its cream. The law
requires that this fact should be stated on the label. Tins which have
bulged should be rejected. Condensed milk is more easily digested
by infants than new cow’s milk, but it lacks the anti-scorbutic
properties of new milk (see page 28). Even the condensed whole milk
if diluted beyond 1 part of milk to 3 of water is deficient in fat.
Sweetened condensed milk has one-third its weight of extraneous sugar
added to it, and on this account it tends in children to produce
fatness, and a distaste for simple food; in children fed on it alone
ossification (formation of bone) is retarded, and resistance to illness
is diminished. The only dietetic advantages it possesses over fresh
cow’s milk are its freedom from possible disease germs and easier

The =digestion of milk= is preceded by its clotting in the stomach.
The same thing happens when =junket= is formed by the addition of
rennet to milk. This is a different process from the curdling of
milk, which occurs when milk turns sour. The latter is caused by the
splitting up of milk sugar and the formation of lactic acid by certain
micro-organisms in the milk. When milk is heated, a skin is formed,
consisting of coagulated albumin, in which is also a little casein,
fat, and salts of lime. Boiled milk becomes sterilized. Cow’s milk
should always be boiled, unless it is quite certain that the cows from
which it is derived are perfectly healthy, and that the milk has not
been exposed to infection before reaching the house. The =disadvantages
of boiling= which are outweighed by its advantages, are that the taste
of the milk is altered, some nutritive matter is lost by the formation
of the “skin,” and the casein is not quite so easily digested.
=Pasteurization= of milk, _i.e._ keeping it at a temperature of 70°
C. (158° F.) for 20 to 30 minutes has been proposed as an alternative
to boiling. This appears to destroy the bacilli causing tuberculosis
(see page 312). The typhoid bacilli are killed at 60° C. in five
minutes when suspended in emulsion. Pasteurization is not, however, so
certainly efficacious for other disease-germs as is boiling, and is not
so easily carried out in domestic life as boiling. By boiling milk in a
double saucepan, _i.e._ in a water-bath, very little change occurs in
the taste of the milk, especially if it be cooled rapidly and strained.

=Cheese= is prepared by coagulating milk by “rennet,” the mucous
membrane of the fourth stomach of the calf, salted and dried before
using. By this means the casein is precipitated, carrying down with
it the cream, and a large proportion of the salts of milk. The whey,
containing the sugar, soluble albumin, and remaining salts, is
separated by straining, while the mixed curd and fat are pressed in
moulds. Cheese thus consists of casein, fat in varying proportions,
water and salts, especially phosphate of lime. It is coloured with
annatto, a vegetable colouring matter. When new, cheese is tough; when
old, its oils tend to become rancid; the best age is from nine to
twenty months. It is probable that cheese in small amount helps the
digestion of other foods, though it is itself a highly concentrated
and comparatively indigestible food. When toasted it is proverbially

There are many different kinds of cheese. The following classification
gives the more important varieties:—

 (1) Cream cheese is the new curd only slightly pressed, and is more
 digestible than ordinary cheese.

 (2) Next to these are cheeses made with whole milk rich in cream, such
 as Stilton, Gorgonzola, Cheshire, and Cheddar.

 (3) Cheeses made of poor or partially skimmed milk, such as
 Shropshire, Single Gloucester, and Gruyère.

 (4) Cheeses made of skimmed milk, such as Suffolk, Parmesan, and Dutch.

American cheeses may belong to any of these classes; they are generally
pure, but occasionally are made from separated milk, margarine being
added to take the place of cream. The sale of such cheeses, except
under the name of “margarine cheese,” is now illegal.

NON-NITROGENOUS ANIMAL FOODS.—These are all fats, and the most
important are the various meat fats and butter. They possess a higher
food value than carbohydrates in the proportion of 2¼ to 1. The
composition of the various fats differs somewhat; they usually contain
varying proportions of olein, palmitin, and stearin, which are
compounds of glycerine with the radicle of a fatty acid (stearin =
C₃H₅ (C_{18}H_{35}O₂)₃). Thus mutton suet consists of stearin, olein,
and palmitin, with a preponderance of stearin. Beef suet contains
less stearin and more olein than mutton suet. The more olein a fat
contains the less solid it is. Olive oil is composed almost entirely of
olein. Palmitin, which melts sooner than stearin, is the chief solid
constituent of butter, while olein is its chief liquid constituent.
Butter is specially distinguished by containing 7 to 8 per cent. of
“volatile fatty acids,” such as butyric, caproic, etc., combined with
glycerine. The presence and amount of these compounds is an important
test for the freedom of butter from adulterating fats.

Cod-liver oil is next to butter the most digestible animal fat known.
The best cod-liver oil is frozen at a low temperature, by which means
the stearin is frozen out, and nearly pure olein is left. Traces of
iodine have been found in it, and more commonly a small amount of bile,
which probably increases its digestibility.

The temperature at which a fat becomes hard is a fair guide to its
digestibility. Thus we know that beef, and still more, mutton fat,
would become solid, under conditions in which bacon dripping is still
soft. Where digestion is weak, there may be an instinctive loathing
of fat meat; for such persons, especially for children, some other
fat should always be substituted. Thus the addition of butter to the
potatoes makes up the deficiency.

=Butter= forms 3½ to 4½ per cent. of cow’s milk. It is separated
from milk by churning, the oil particles being deprived by this means
of their albuminous coats. The more completely the butter-milk is
separated the longer the butter keeps. It can be kept longer if salt is
added, or in hot weather by keeping it under frequently-changed water.
Rancidity indicates the decomposition of traces of the fat of butter
into its fatty acid and glycerine.

Cream contains about 30 per cent. of butter fat, Cheshire cheese 25 per
cent., and skim milk cheese 7 per cent.

Butter milk differs from skim milk in the presence of lactic acid.
It is more digestible than skim milk, the casein being in a more
flocculent condition.

The odour and flavour of butter are not due to olein and palmitin, the
two chief constituents, but to a smaller quantity of butyrin, caproin,
and caprylin fats of a much lower series. Ordinary butter contains
a considerable proportion of water, and the presence of about 8 per
cent. renders it more palatable; if it is over 15 per cent., the butter
is considered adulterated. An excessive amount of salt is sometimes
present. The most frequent adulteration is the substitution of foreign
fats for butter fat, _e.g._ lard, palm oil, rape seed oil, or cocoa-nut
oil. Margarine is most frequently used for this purpose.

=Margarine= is prepared from beef-fat by melting, the stearin
becoming solid again at a temperature at which olein and margarine
still remain liquid. It forms a wholesome and cheap food, being
nearly as digestible as butter, for which more expensive food it
is often fraudulently sold. When mixed with a small proportion of
butter its recognition by smell, etc., is almost impossible, but
on careful chemical analysis, it is found to have a higher melting
point and a lower specific gravity than butter, and a much smaller
percentage of soluble fatty acids than the latter. Thus:—
│           │ POINT.   │ GRAVITY. │     OF INSOLUBLE FATTY ACID.     │
│_Butter_   │ 32° C.   │    .913  │ 88 per cent. insoluble fatty acid│
│_Margarine_│ 35° C.[1]│ .904─.907│ 95[2]             „      „     „ │

CEREAL FOODS.—Gluten is peculiar to plants, and is chiefly found in
plants belonging to the great family of grasses. Gluten is to bread
what casein is to milk, and myosin to flesh. If one takes a piece of
dough made from wheat flour, and holds it under a stream of water from
the tap, a large part of it is washed away, while a sticky adherent
mass is left behind. This is gluten, and it is its tenacity which
enables bread to be made. If the fluid with which the dough was washed
is collected, it will be found to contain a large quantity of starch,
a small amount of sugar, of albumin, and certain salts. All cereals
possess these constituents in various proportions, as may be seen from
the following table:—

  │              │      │        │    │              │          │MATTER.│
  │              ├──────┼────────┼────┼──────────────┼──────────┼───────┤
  │_Wheatmeal_   │ 12.1 │  12.9  │1.9 │     70.3     │   1.6    │  1.2  │
  │_Fine wheat   │      │        │    │              │          │       │
  │   flour_     │ 13.0 │   9.5  │0.8 │     75.3     │   0.7    │  0.7  │
  │_Oatmeal_     │  7.2 │  14.2  │7.3 │     65.9     │   3.5    │  1.9  │
  │_Barley meal_ │ 11.9 │  10.0  │2.2 │     71.5     │   1.8    │  2.6  │
  │_Maize meal_  │ 11.4 │   8.5  │4.6 │     72.8     │   1.4    │  1.3  │
  │_Rice (husk   │      │        │    │              │          │       │
  │   removed)_  │ 12.0 │   7.2  │2.0 │     76.8     │   1.0    │  1.0  │

The proteid varies in character in the different cereals; wheat flour
has the largest proportion of gluten (8 to 12 per cent.) and therefore
makes the best bread.

Good =wheat flour= ought to be white, not gritty or lumpy, not acid
or musty, forming a coherent stringy dough. Examined microscopically,
it should show the absence of any fungi, or acarus farinæ, or of
foreign starches, such as barley, maize, rice, potato, known by the
different shape of their starch granules. (See Fig. 1.) Alum has been
occasionally added to flour, to enable the baker to make a white
and porous bread from damaged wheat flour. It can be detected as
follows:—Pour over the freshly cut surface of a slice of bread some
freshly prepared decoction of logwood chips, and then a solution of
carbonate of ammonia. If alum is present, the bread turns a marked blue
to violet colour; but if the bread is pure, it is only stained pink.

The wheat grain may be used as food in its entirety. Thus boiled in
milk, after having been soaked in water, it forms the chief constituent
of _frumenty_. Usually it is converted into flour by grinding or
milling. A grain of wheat consists of three parts, an outer envelope,
the _bran_, consisting chiefly of indigestible cellulose, and composing
13½ per cent. of the grain; the kernel, or _endosperm_, which
makes up 85 per cent. of the grain; and the _germ_, forming 1½
per cent. of the grain. In the old method of stone grinding, the
bran was removed, and the germ left along with the endosperm. In the
elaborate processes of modern roller milling, the bran is removed as
in the old grinding, because it cannot without the greatest difficulty
be reduced to powder; and the germ is also removed, because the oil
abundantly present in it is apt to become rancid and spoil the flour,
and because the soluble proteids in it are apt to change some of the
flour into dextrin and sugar, which become brown in baking and spoil
the appearance of the bread. The germ is easily removed, because
its toughness causes it to be flattened out in the milling, while
the endosperm becomes powdery. The central part of the endosperm is
the source of ‘patents.’ It is very rich in starch and is used for
making fancy breads and pastry. The outer part of the endosperm is
‘households.’ ‘Households flour’ is subdivided into (_a_) second
patents, or ‘whites’; (_b_) first households; (_c_) second households
or ‘seconds.’ ‘Seconds’ is richest in gluten, ‘whites’ in starch.
Ordinary bread is normally derived from a blend of these three. Some
‘strong’ wheats, _e.g._ Australian, yield a ‘patents’ which is rich
in gluten, and such flour is used for making Vienna bread. ‘Strong’
wheats take up most water in baking, and so yield most loaves per
sack. ‘Seconds’ flour yields a bread which is richer in proteid than
most other kinds; but the dark colour of the loaf makes it unpopular.
Various schemes have been devised to utilise the germ and the bran,
which are ordinarily discarded. In the preparation of _Hovis flour_ the
separated germ is partially cooked by superheated steam. This kills the
ferment contained in the soluble proteids, and thus prevents it from
changing starch into maltose and dextrin. The action thus prevented is
represented by the following formula:—

      STARCH.             MALTOSE.     DEXTRIN.

  10 C₁₂H₂₀O₁₀ + 6 H₂0 = 6 C₁₂H₂₂O₁₁ + 4 C₁₂H₂₀O₁₀.

The germ thus treated is ground to a fine meal, of which one part to
three of ordinary flour, forms Hovis flour. Other ‘germ breads’ are
also in the market. In the making of _Frame food_ the bran is boiled
with water under high pressure. The watery extract, containing the
mineral and part of the nitrogenous constituents of the bran, is
evaporated to dryness, and forms the basis of various preparations. It
is doubtful if this food possesses any great value.

=Brown bread= is a somewhat vague expression, meaning either an
admixture of bran or of germ or of both with flour, or bread made
from whole wheat flour. In each of these cases the loaf would be
brown. The bran is rich in fat as well as in phosphates. It acts as a
mechanical irritant, ill borne by delicate stomachs, but very useful
where a tendency to constipation exists. The excess of nitrogenous
matter in brown bread and its richness in fat, do not prove its greater
nutritiveness, as it is present in a condition in which only a portion
is absorbable from the alimentary canal into the circulation.

The harder wheats, such as Sicilian wheat, contain a larger percentage
of gluten; and from them _macaroni_ and _vermicelli_ are obtained,
which are nearly pure gluten. They are very nutritious and useful
foods. _Semolina_ is prepared from wheat, the millstones being left
sufficiently apart to leave the product in a granular condition. In
_malted_ breads, a syrupy infusion of malted barley (malt extract) is
added to the flour. Malt extract contains in addition to malt sugar
(maltose) and dextrins, a ferment (diastase) which, like the saliva,
is able to convert starch into the soluble substances, maltose and
dextrin (see formulæ above). The action of this ferment is stopped by
the temperature of baking. Hence even when the malt extract is allowed
a considerable time for its operation on the dough, only about 10 per
cent. of the starch in the loaf becomes soluble, as compared with 4 per
cent. in an ordinary loaf.

=Oatmeal=, obtained from the common oat, contains very little gluten,
and so cannot be made into vesiculated bread. It contains a large
proportion of other nitrogenous material and of fat. As porridge and
oatmeal cake it forms a very nutritious diet. The husk ought to be
carefully removed from the meal intended for human food, as, although
very nitrogenous, it acts as a mechanical irritant. Groats consists of
oats from which the husk has been entirely removed. The substitution of
rolling for grinding in preparing oats for food and the application of
heat during the rolling process, have made oatmeal more digestible, as
in Quaker, Provost, and Waverley oats.

=Barley= contains very little gluten; on this account, like oatmeal, it
does not admit of being made easily into bread.

=Malt= is barley which has been made to germinate by heat and moisture
and then dried, “diastase” being formed in the process. _Extract of
malt_, containing diastase in an active condition, is useful in cases
of impaired digestion and deficient assimilation of food.

=Rye= is rarely used in this country for making bread. In Germany
it is known as “black bread,” but its colour and acid taste make it
disagreeable, and it is laxative in its action.

=Maize=, or =Indian Corn=, is deficient in gluten, and so not suitable
for making vesiculated bread. Like oatmeal, it is made into cakes,
called in America “Johnny cake.” It contains much fatty matter, and
is largely used for fattening poultry and other animals. Oswego flour
and corn flour are maize flour deprived by a weak solution of soda, of
its proteids and fat; hominy contains all its constituents. Maize is a
cheap and nutritious food. When wheat flour is dear, it is occasionally
adulterated with maize. The adulteration can be detected by the forms
of the starch granules, examined under a low power of the microscope.

=Rice= contains less proteids and fat than any other cereal. Its chief
value as a food depends on the large amount of starch it contains
(table, page 16).

LEGUMINOUS FOODS.—The chief seeds belonging to this group are peas,
beans, and lentils. They contain a smaller proportion of starch, and
a larger proportion of nitrogenous materials than cereals. Thus while
flour contains 9.5 and bread 8 per cent. of proteid, lean meat 15.18
per cent., and cheese about 30 per cent., peas and beans contain 21 to
26 per cent. (green peas only 4 per cent., dried peas 21 per cent.)
of proteid. The nitrogenous material exists chiefly as legumin, which
has been called vegetable casein. Although leguminous seeds contain
more nutritive material in a given weight than cereals, dietetically
they are inferior, owing to the fact that they are less digestible,
often causing flatulence and other dyspeptic symptoms. Cereals, again,
are more palatable than leguminous seeds, and are more prolific,
and consequently cheaper. In the absence of animal food, legumens
form a useful substitute. They are advantageously diluted with oily
substances, or with rice. The farm-labourer’s dish of broad beans and
fat bacon is founded on strict physiological principles. A mixture of
lentil and barley flour is sold under the name of Revalenta Arabica.
Lentil flour costs 2½d., Revalenta 3s. 6d. per lb. Green peas,
French beans, and scarlet runners are much more easily digested than
are dried peas or beans. Lentils contain the largest proportion of
proteid of any of the pulses. They also contain very little sulphur,
and so do not give rise to the same liberation of sulphuretted hydrogen
in the intestine, as other pulses. The ash of the Egyptian lentil is
particularly rich in iron.

AMYLACEOUS FOODS. Amylaceous or starchy substances are contained in
many of the preceding foods; but some other foods consist almost
entirely of starch. The chief of these are sago, tapioca, and arrowroot.

=Sago= is obtained from the pith of the stems of various species of
palm; a single tree may yield several hundred pounds. Alone it is
easy of digestion. Boiled with milk it forms a light, nutritious, and
non-irritating food. Fictitious sagos are frequently sold, made from
potato starch.

=Tapioca and Cassava= are derived from the tubers of more than one
species of the poisonous family, Euphorbiaceæ. The juices are removed,
and the prussic acid removed by heat. Tapioca only differs from cassava
in being a purer form of starch; the latter is more nutritious, and
among the Indians takes the place of bread.

=Arrowroot= is obtained from the tubers of _Maranta Arundinacea_.

=Tous-les-mois= is a form of starch obtained from the tubers of a West
Indian plant, the _Canna edulis_.

[Illustration: Potato. Wheat. Rice. Oats. Barley. Pea. FIG.

The =detection= of the varieties of =starch= is usually possible owing
to their fairly characteristic appearance under the microscope. Fig.
1 shows the most important starches. It must be noted that in oats,
maize, and rice the contour is completely marked by facets or surfaces,
while there are less complete markings in tapioca and sago. In wheat,
rye, pea, bean, barley, potato, and arrowroot the contour is even,
though there are minor differences of size and shape.

OTHER VEGETABLE FOODS.—=Green Vegetables= contain comparatively little
nutriment, but form valuable additions to other foods. Cellulose, which
forms their main constituent, although indigestible, forms a bulk
in the alimentary canal, which is necessary to ensure peristalsis.
Concentrated nourishment can only be digested in limited quantity, and
is very apt to produce digestive disorder. Cabbage contains 92 per
cent. of water, and 2½ per cent. nitrogenous matter. Carrots contain
6 per cent. and turnips 2 per cent. of nitrogenous matter; parsnips
are intermediate between these. Green vegetables possess valuable
anti-scorbutic properties. They may be made an important vehicle for
giving fatty food, by adding butter, etc.

Rhubarb and sorrel contain oxalates and tartrates of potash and lime,
to which they owe their tartness. Spinach is cooling and laxative,
like rhubarb, but not tart. Sea-kale, artichoke, and asparagus are
all wholesome vegetables. Asparagus is somewhat diuretic, and gives
a peculiar, disagreeable odour to the urine. Salads, such as mustard
and cress, water-cress, endive, and the garden lettuce are very useful
as anti-scorbutics. Some of them possess a peculiar pungency due to a
volatile oil analogous to that contained in horse-radish.

The =Potato= contains 26 solid parts in 100, of which nearly 20
are starch and 2½ nitrogenous matter. It forms one of our
best-appreciated vegetable foods, and as it possesses valuable
anti-scorbutic properties, its universal use is, perhaps, the chief
cause of the present rarity of scurvy. Alone, it possesses too small a
proportion of nitrogenous material to support life, but the addition
of butter milk makes up this deficiency; and these two together form a
sufficient diet to maintain life and health for a long time.

The =Onion=, =Garlic=, =Leek=, and =Shalot=, all members of the lily
family, are chiefly used as condiments. They contain an acid volatile
oil, which gives them a peculiar odour and flavour. By long boiling,
this is dissipated (as in the case of the Spanish onion), and the onion
is then fairly digestible, as well as nutritious.

=Celery= possesses a more delicate flavour and odour than the
preceding, but even the most tender celery is digested with difficulty;
less so, when boiled or stewed, or a constituent of soups.

Only four =Fungi= are, with us, commonly regarded as safe—mushrooms,
champignons, morels, and truffles; but there are many others which are
equally edible. The food value of fungi has been exaggerated. They are
difficult of digestion and contain little nutritive material. Poisonous
fungi usually have an astringent styptic taste and a disagreeable
pungent odour. In any doubtful case it is better to abstain.

=Oily Seeds= contain a considerable amount of fixed oil which renders
them unfit for persons of weak digestion. The almond, walnut,
hazel-nut, and cocoa-nut are common examples. The sweet almond, when
eaten unbleached, occasionally produces nettlerash, and its solid
texture and large proportion of fixed oils render it difficult of
digestion. The _chestnut_ contains less oil, but a large amount of
carbohydrate. It is extensively used as a food in Italy and some other
countries. In the uncooked condition it is very difficult of digestion.

=Fruits= are chiefly used as adjuncts to other foods; but the vegetable
salts and the cellulose and sugar which they contain, make them very
valuable. =Cucurbitaceous= fruits are used as vegetables rather than
as fruits. Vegetable marrow is wholesome and agreeable, but not very
nutritive. Cucumber is most digestible when rapidly grown and freshly

=Stone-fruits= or drupes, such as the peach, nectarine, plum, cherry,
are rather luxuries than foods, like many other fruits. Before ripening
they are unfit for food; when ripening is complete, the acids and
astringent matter largely disappear. The _date_ contains chiefly sugar,
and forms an important food in the East.

=Pomaceous Fruits=, as the apple, pear, and quince, are more digestible
when cooked; and, speaking generally, all fruit not perfectly ripe
should be cooked before eating. The presence of vegetable acids in
fruit soon converts the sucrose of cane sugar into dextrose, a less
sweet variety of sugar. It is therefore more economical to sweeten
after than before cooking.

The chief =Berries= are the grape, currant, gooseberry, cranberry, and
elderberry. The grape is the most important, and 1,500 varieties of it
have been described. Its juice contains a large amount of grape sugar
(dextrose), and small quantities of glutinous material, bitartrate of
potash, tartrate of lime, malic acid, etc.

Besides the above fruits, we have strawberries, mulberries, figs,
plantains, melons, etc., which are all refreshing and anti-scorbutic.
The orange family furnishes us with the orange, lemon, citron, lime,
shaddock, and pomelo, of which the orange is by far the most important,
and possesses most valuable refreshing qualities.

=Sugar= exists in two chief forms, viz. sucroses and glucoses.
=Sucroses=, known chemically as disaccharids (Sucrose = C_12H_22O_11;
compare starch = C_12H_20O_10) are exemplified in cane, beet, maple,
malt (maltose), and milk sugar (lactose). Cane sugar has been gradually
displaced by beet sugar. The two are chemically identical, and equally
nutritious. Maltose is given in malt extract as a food, and because of
the digestive action of the ferment also contained in the extract on
starchy food. Thus:—

        STARCH.            MALTOSE.
  C_12H_20O_10 + H_2O = C_12H_22O_11.

Lactose is comparatively free from sweetness, and is hardly capable of
being fermented by yeasts.

Of =Glucoses= the best example is dextrose = C_6H_12O_6, H_2O,
which can be seen crystallised in dried raisins; it only possesses
one-third the sweetening power of sucrose. Starchy food becomes
changed into glucose by the action of saliva and pancreatic juice in
the alimentary canal. Grapes, cherries, gooseberries, figs, and honey
contain lævulose in addition to glucose (glucose = C_6H_12O_6, H_2O,
lævulose = C_6H_12O_6). Lævulose resembles dextrose except in being
uncrystalline, and in its effect on polarised light. Many ripe fruits,
such as pineapples, strawberries, peaches, citrons, contain sucrose and
lævulose, the latter being not quite so sweet as sucrose.

In the alimentary canal sucroses are inverted into dextrose and
lævulose. Thus natural foods containing these sugars are more readily
assimilated than those containing sucrose.

The sweetening power of the varieties of sugar depends on their degree
of solubility in water. Sucrose is soluble in one-third of its weight
of cold, and in rather more of hot water. Dextrose is soluble in its
own weight of water; lævulose is more soluble, and therefore sweeter
than dextrose. Lactose requires five to six parts of cold and two of
hot water, and is therefore not so sweet as the other varieties.



Diseases may arise from the noxious character or from deficiency or
excess of some particular food, or of the food as a whole.

DISEASES FROM UNWHOLESOME FOOD.—I. =The Meat of Diseased Animals.=

(1) _The flesh of animals which have not been slaughtered_ should be
prohibited from sale, whether death has resulted from accident or
disease. The meat from diseased animals is also generally dangerous,
sometimes owing to the _drugs_ with which the animals have been dosed
before death, _e.g._ tartar emetic, or opium.

(2) Meat may be unwholesome from _the presence of parasites_. Of these
the most common is—

(_a_) The =cysticercus cellulosæ=, which is the undeveloped embryo of
the tape-worm; that from the pig becomes the tænia mediocanellata. The
cysticercus of the pig is the most common; it forms a cyst about the
size of a hemp-seed, commonest on the under surface of the tongue. In
hams oval holes are found or opaque white specks, which are the remains
of the cysts converted into calcareous matter. When meat containing
the cysticercus alive (as in under-cooked or raw meat) is swallowed,
it develops into the tape-worm, which consists of a number of flat
segments, each capable of producing numerous ova of new cysticerci,
with a minute head at the narrow end surrounded by hooklets. A
temperature of 174° F. kills the cysticercus. Another kind of tape-worm
common on the continent, called _bothriocephalus latus_, is derived
from the cysticercus of fish.

[Illustration: FIG. 2.



(_b_) The =trichina spiralis= is not a solid worm like the tænia, but
possesses an intestine. In pork it forms a minute white speck, just
visible to the naked eye, which forms a nest, and in this one or two
coiled up worms can be seen by a magnifying glass in active movement.
They are effectually killed by the temperature of boiling water; but
no form of drying, salting, or even smoking at a low temperature is
sufficient for this purpose. Boiling or roasting does not suffice to
destroy all the trichinæ unless the joint is completely cooked in its
interior. When trichinous pork is swallowed, the eggs develop in the
alimentary canal in about a week into complete worms, and in three or
four days more each female produces over a hundred young ones. These
burrow into every part of the body, producing great irritation and
inflammation. In one case after death upwards of 50,000 worms were
estimated to exist in a square inch of muscle. Most of the cases of
trichinosis have occurred in Germany, from eating imperfectly cooked
sausages. The pig becomes trichinous by eating offal, and man is
infected by eating pork. This disease is rare in England.

[Illustration: FIG. 3.



(3) =Tuberculous Meat=, from animals suffering from tuberculosis, has
been found to cause tuberculosis in small animals experimentally fed
on it. Koch has recently thrown doubt on the communicability of bovine
tuberculosis to man; but this point must be regarded as still unsettled
(see page 312). Sheep are rarely affected by it, but it is very
common in cattle, especially in cows, and it is a serious economical
question whether the meat of all such animals should be condemned.
The ideal would be to condemn all such animals, as tuberculosis is an
infective disease, and the bacillus which causes it (as well as the
toxic products of its activity) may be present in meat which shows no
actual signs of disease, except in the lungs or other internal organs.
In practice, however, the rules laid down by the Royal Commission on
Tuberculosis, in 1898, should be followed for the present. These state

 “The entire carcase and all the organs may be seized (_a_) when
 there is miliary tuberculosis of both lungs, (_b_) when tuberculous
 lesions are present on the pleura and peritoneum, or (_c_) in the
 muscular system, or in the lymphatic glands embedded in or between
 the muscles, or (_d_) when tuberculous lesions exist in any part of
 an emaciated carcase. The carcase, if otherwise healthy, shall not be
 condemned, but every part of it containing tuberculous lesions shall
 be seized (_a_) when the lesions are confined to the lungs and the
 thoracic lymphatic glands, (_b_) when the lesions are confined to the
 liver, (_c_) or to the pharyngeal lymphatic glands, or (_d_) to any
 combination of the foregoing, but are collectively small in extent.”
 They also add that any degree of tuberculosis in the pig should secure
 the condemnation of the entire carcase, owing to the greater tendency
 to generalisation of tuberculosis in this animal; and that in foreign
 meat, seizure should ensue in every case where the pleura has been
 “stripped.” (See also page 312.)

(4) Other =Infective diseases= besides tuberculosis may render
meat wholly or partially unfit for food. Of these pleuro-pneumonia
may not require condemnation of the entire carcase; but in the
following this course should be adopted, cattle-plague, pig typhoid
(pneumo-enteritis), anthrax, and quarter ill, as well as in sheep-pox.
In puerperal fever, actinomycosis, and sheep-rot (liver flukes) each
case must be decided on its merits.

II.—=Decomposed Meat.=—Putrid meat has often produced diarrhœa and
other severe symptoms. Putrid sausages are especially dangerous, and
incipient putridity seems to be more dangerous than advanced.

=Tinned Meats= occasionally produce severe illness, which has been in
several cases fatal. It is important to secure a good brand, and to eat
the meat as early as possible after the tin is opened. Tins in which
any bulging is present, showing the presence of putrefactive gases,
must be rejected; and still more tins which have been pricked and
resoldered in a second place. All tinned meats and fruits are stated by
Hehner to contain compounds of tin in solution. These do not seem to be
perceptibly injurious, unlike lead salts, which are now rarely found.

The general subject of =Meat Poisoning= has had much light thrown on
it during the last few years. Brieger, about 1886, showed that during
the cultivation of bacteria, alkaloidal bodies known as ptomaines
and leucomaines, were formed, which were virulently poisonous. It
was commonly supposed that the poisoning occasionally produced by
eating meat pies, sausages, hams, brawn, and similar food, was due to
these ptomaines. It is now known, however, that there are far more
important =toxines= than the alkaloidal, which result from bacterial
life in meat, etc. (see page 286). These are more closely related to
substances of an albuminous or proteid nature than the ptomaines.
These toxines may be fatal when as small a dose as a fraction of a
milligramme (mgm. = about 1∕64 grain) is given subcutaneously. The
evidence now shows that neither ptomaines nor other toxines (albumoses)
or any other bacterial products besides these, cause the outbreaks of
acute poisoning occasionally traced to food, but that these are due
to bacteria. There is, in other words, actual _infection_, as well as
_poisoning_. The microbe chiefly found as the cause of these outbreaks
is the _Bacillus enteritidis of Gaertner_, and some allied microbes. In
an outbreak at Oldham, 160 pies made on a Thursday, from the veal of a
calf killed on the preceding Tuesday, were baked in several batches,
and of the persons eating these pies fifty-four became ill. That the
contamination was not introduced after cooking was shown by the fact
that several persons were made ill who ate pies still warm from baking.
The facts indicated that one batch was imperfectly cooked, the time
allowed being only twenty minutes, as compared with fifty minutes
allowed in corresponding cooking in domestic life. Experimentally it
has been found that an exposure for one minute to 70° C. kills the
_Bacillus enteritidis of Gaertner_. That this bacillus was the cause of
the outbreak was subsequently shown by the fact that the serum of blood
taken from some of the patients showed characteristic clumping with
a pure culture of this bacillus, just as happens with the blood of a
patient suffering from enteric fever when a cultivation of the microbe
of this fever is mixed with it (see page 301). In this outbreak the
symptoms were usually diarrhœa, vomiting, intense thirst, desquamation
of the skin, and a slow convalescence, lasting from three to six weeks.
(See page 26 for poisoning by _Bacillus enteritidis sporogenes_.)

III.—=Meat injuries from the food eaten before killing.=—Pheasants fed
on laurel, hares on rhododendron chrysanthemum, and other animals fed
on the lotus, wild cucumber, and wild melon of Australia, have caused
dangerous symptoms.

IV.—=Fish=, especially some kinds, occasionally produce nettlerash and
other disorders, especially in warm weather. Leprosy has been ascribed
to the eating of decomposing fish, but it occurs in countries where a
fish diet is impossible.

Shell-fish and crustaceans (as lobster, crab) are very prone to produce
evil results. Shell-fish (mollusca), such as mussels, cockles, and
oysters, are dangerous foods. They are generally grown in estuaries,
to which the sewage of towns has access; and not infrequently cases
of enteric (typhoid) fever, as well as more acute attacks of diarrhœa
and vomiting, have been traced to them. Mussels and cockles are seldom
sufficiently cooked to render them safe; and oysters are eaten raw.
They should never be eaten, unless from personal direct knowledge it is
certain that they have been derived from an estuary in which there was
no possibility of contamination by sewage.

V.—=Milk= has been a common carrier of disease. Cows eating the rhus
toxicodendron get the “trembles,” and their milk produces serious
gastric irritation in young children. The milk of goats fed on wild
herbs or spurgeworts has produced severe disorders.

The milk of animals suffering from foot-and-mouth disease, although
frequently drunk with impunity, occasionally produces inflammation of
the mouth (aphthous ulceration). The milk derived from cows fed on
grass from sewage farms is, _per se_, as wholesome as any other, and
its butter has no more tendency to become putrid than that derived from
any other source.

The great dangers in respect to milk are of its becoming mixed with
contaminated water; or of its absorbing foul odours. The absorptive
power of milk for any vapour in its neighbourhood, is shewn by exposing
it in an atmosphere containing a trace of carbolic acid vapour: the
milk speedily tastes of the acid.

Milk also tends to undergo rapid fermentative changes, especially in
warm weather, or when tainted by traces of putrefying animal matter.
Diarrhœa in children is frequently due to such a condition, or to
the rapid decomposition of milk in an imperfectly cleaned bottle.
Milk should always be boiled in warm weather; and it should never be
stored in ill-ventilated larders, or where there is a possibility of
the access of drain effluvia; nor ought it to be kept in lead or zinc

 Epidemic diarrhœa has been ascribed by Klein to a microbe called the
 _Bacillus enteritidis sporogenes_. This is not killed by heating
 the liquid containing it to 80°C. for twelve to fifteen minutes,
 as is the typhoid bacillus and other non-spore-forming bacilli. In
 an outbreak of diarrhœa among the patients in St. Bartholomew’s
 Hospital, London, there was strong evidence that this microbe taken
 in rice pudding had caused the mischief. Eighty-four patients and two
 nurses were attacked, and the patients who had eaten rice pudding
 were almost exclusively attacked. A portion of this pudding after
 being kept twenty-four hours was found sour and acid. The _Bac.
 enteritidis sporog._ was found in it. Furthermore it was shewn
 that the temperature at which the rice puddings were cooked never
 exceeded 98°C., whereas the spores of this microbe withstand 100°F. a
 considerable time.

Very many epidemics of enteric fever and scarlet fever, and a smaller
number of epidemics of diphtheria have been traced to contaminated
milk. Usually in enteric fever the contamination of the milk was
traced to the use of water “for washing the milk-cans,” derived from
specifically polluted sources, and doubtless the water was the real
source of the disease. In most of the milk outbreaks of scarlet fever,
either there was scarlet fever in the dairy, or persons employed in
the dairy were in attendance on patients suffering from the disease;
but in an outbreak connected with a supply of milk from Hendon, it was
suspected that a certain eruptive disease of the udders of the cow
might have been the cause of scarlet fever in man, without infection
from a previous case of the disease. This point is still _sub judice_.

Tubercular disease of the intestines and mesenteric glands may be
produced by taking milk derived from tuberculous cows. This was proved
in the case of calves (page 311), and there are strong reasons for
thinking that the same is true for infants, though doubt has been
thrown by Koch on the communicability of bovine tuberculosis to the
human being. The only safe plan is to sterilise the milk (page 13).

VII.—=Vegetable Food= (especially greens) is indigestible if stale,
and all mouldy vegetables are dangerous. Over-ripe and rotten fruit is
liable to produce diarrhœa; but the diarrhœa prevalent in summer is due
much less to this than to other decomposing foods, particularly milk.

Poisonous symptoms have been produced by the admixture of _darnel_
(lolium temulentum) with flour.

The eating of _damaged maize_ in Italy is the cause of an endemic skin
disease, called _pellagra_, which commonly proves fatal.

_Ergotism_ is due to the growth on cereals (and most commonly on the
rye) of a poisonous fungus, the _claviceps purpurea_, which produces
a deep purple deposit on the grain. If bread made from such flour is
eaten for prolonged periods, severe symptoms result; in some cases,
a dry rotting of the limbs. There have been several epidemics on the
continent, due chiefly to eating bad rye bread.

=Starvation Diseases.=—_Simple Starvation_ causes death in a period
varying with the previous state of nutrition. Usually death occurs when
the body has lost two-fifths of its weight, whether this be after days,
months, or years (Chossat). A supply of water prolongs the duration
of life, to as much as three times what it would otherwise be. Good
nourishment doubles the power of resisting disease; while deficient
food prepares the way for many diseases. A large share of the decline
in the English death-rate during the last forty years is due to free
trade, and the great cheapening of wholesome food which has resulted
from it.

An ill-balanced is more frequent than a deficient diet. Deficiency of
fat is more serious than deficiency of carbohydrates, and deficiency of
proteid is most serious.

=Scurvy= is caused by the absence of fresh vegetables. The use of the
potato and the orange, as well as of lime juice (the juice of citrus
limetta), has led to its extinction among adults in this country. In
former times, it caused more deaths among seamen than all other causes
put together, including the accidents of war. In infants fed upon
tinned foods, whether condensed milk or patent foods, a form of scurvy
still occurs. Infants fed on new-milk never suffer in this way. If,
therefore, it is necessary to feed an infant on condensed milk for many
consecutive months, potato gruel or raw meat juice or fresh milk must
occasionally be given.

_Rickets_ is chiefly due to improper feeding in childhood. The
substitution of artificial foods (most of them containing starch) for
the natural milk is its chief cause. The lower incisor teeth of an
infant appear between the sixth and seventh months. Starchy food given
before this age is undigested. Such food likewise leads to less fat
and proteid being given, which are essential for growth. Deficiency of
lime salts in the food does not cause it, and giving them in food or
medicine will not cure it. Enrichment of the diet by cream or failing
this by cod liver oil is the best means of preventing and curing it.
Abundant fresh air and warm clothing are also necessary.

_Relapsing fever_ generally follows epidemics of typhus fever, and is
greatly favoured by starvation. Ophthalmia has been chiefly prevalent
in charity schools in which the children are underfed, though its
essential cause is contagion.

=Diseases Connected with Over-Feeding.=—A fire may go out for want of
fuel, or from becoming choked with ashes; and it is the latter state
of things which occurs in =Gout= and allied diseases. Weakness is
commonly complained of, but this is due to excess of food embarrassing
vital action; and abstinence and exercise are required to restore the
balance. Excess of nitrogenous food—especially if combined with the use
of sweet, or strong, or very acid wines, and beer—is particularly prone
to produce gout. In these cases, animal food should only be taken once
a day, and vegetable food should be allowed to preponderate.

=Obesity= is favoured by excess of starchy food and sugar, and by
copious drinking of water or other beverages. The plan of curing
obesity by restricting oneself almost entirely to meat food is
only advisable, however, under certain conditions. =Gall-stones=
are favoured by rich foods and excess of sugar; also by alcoholic
indulgence. =Dyspepsia= is commonly due to loading the stomach at too
frequent intervals; but on the other hand, it not infrequently leads to
the taking of insufficient food, because of the discomfort produced.
The result of this is that a chronic starvation results, with impaired
vital powers. Dyspeptic patients should abstain from pastry and from
tea and coffee, except in small quantities. Alcohol in any form, as a
rule, does harm. Not uncommonly mastication is imperfectly performed,
and a good dentist may cure the indigestion which has resisted all
other treatment.



The importance of a duly proportioned and sufficient dietary is shown
by its great influence on health and constitution. An ill-proportioned
or deficient diet is certain to lead to failure of health. The anatomy
of an animal may be modified in the course of generations by altered
diet, as well as its character; thus, the alimentary canal of the cat
has increased in length to adapt it to its omnivorous habits. In the
case of the bee we have a still more remarkable instance. If by any
accident the queen bee dies, or is lost, the working bees (which are
sexually undeveloped) select two or three eggs, which they hatch in
large cells, and then feed the maggot on a stimulating jelly, different
from that supplied to the other maggots, thus producing a queen bee.

The food of mankind varies naturally with—

I.—_Climate._ A cold climate leads to increased metabolism, and
consequently a large amount of fatty matter can be eaten without
producing nausea. Witness the difference between a Laplander’s and a
Hindoo’s diet.

The _season_ of the year has likewise some influence. Vital processes
are more active in spring than autumn, and more food is consequently
required in the former season.

II.—_Occupation._ Although muscular exercise is not associated with
an immediate increase of elimination of urea, yet as a matter of
experience more nitrogenous food is required and can be metabolised
by hard workers than by idlers. The trappers on the North American
prairies can live for weeks together on meat alone, accompanied
by copious draughts of tea. They are constantly in the open air,
undergoing fatiguing exercises, in a dry and rare atmosphere. For
brain workers no special food is required. Foods containing phosphorus
have no special value, so far as is known, for mental work. Such work,
however, is apt to affect digestion; consequently the digestibility of
food is more important for those engaged in sedentary occupations than
its chemical composition.

III.—_Sex._ As a rule, women require about one-tenth less food than
men, but probably this rule hardly holds good in the case of women
engaged in laborious work.

IV.—_Age._ Infants require only milk, and the less they have of any
other food before a year old the better. Atwater has calculated that——

  A child under 2 requires 3∕10 the food of a man doing moderate work.
      „   of 3 to 5   „    4∕10     „         „        „        „
      „   of 6 to 9   „    5∕10     „         „        „        „
      „  of 10 to 13  „    6∕10     „         „        „        „
  A girl of 14 to 16  „    7∕10     „         „        „        „
  A boy of 14 to 16   „    8∕10     „         „        „        „

Vital processes are more active in early life, and food is required
not only to carry on the functions of the body, but also to furnish
the materials for growth. Hence, while the proportion of proteids to
carbohydrates and fats should be—

 As 1:5.3 in adults, it should be about as 1:4.3 in children.

After the age of thirty-five or forty, the tendency is to take too much
food. All the tissues of the body are established, and excess of food
(especially nitrogenous food) is liable to produce tissue degeneration
by loading the system with partially metabolised matter, and may lead
to gouty diseases. It is much safer to take what may be regarded as too
little than too much food after this period.

=Times for Eating.=—The best arrangement seems to be to have three
meals, each fairly nutritious, and containing all the constituents
required. The Romans only had two meals daily, prandium and cœna. This
is common among the French at present, but it tends to overloading the
digestive organs at these meals.

An ordinary full meal has usually passed from the stomach in four
hours. Fresh food ought never to be introduced before this period; it
is advisable to allow an interval of five hours between meals for the
healthy, so as to give time for the digestive organs to rest, and for
the absorption of food. The practice of taking tea with the chief meal,
or a “meat tea,” is bad. Tea is better taken an hour or two after food.

Regularity in the time of taking meals is important, as the digestive
organs acquire habits like other parts of the body. Work ought not, if
possible, to be resumed immediately after meals, nor active exercise of
any kind. These tend to abstract blood from the digestive organs, and
so diminish the efficiency of digestion.

=Vegetable and Animal Foods.=—The fact that the food we require can
be obtained from the vegetable world has led to the proposition that
vegetable food should be taken alone. It is urged in favour of this
plan, that a large amount of suffering to animals would be prevented.
Also that animal food is not so economical as vegetable, land being
more economically employed in producing corn than in feeding cattle.
Thirdly, there is the indubitable fact that health can be maintained
for prolonged periods on vegetable food (including nuts, cereals,
fruits, etc.)

On the other hand, the chief objections to a purely vegetable diet are
that the undigested refuse is greater than with an equal quantity of
animal food; that a longer time and more exertion than for animal foods
are required in digesting the most nutritious vegetable foods, such
as legumens, while other vegetable foods do not contain a sufficient
proportion of nitrogenous material. Also, if one lived entirely on
vegetable food, a greater bulk would be required, and owing to the fact
that such food is less easily absorbed, satisfaction to the appetite
would not so soon be produced. Animal food has a great advantage as
regards convenience. Man is not an eating machine; he requires food
which is easily converted into the body substance, and this is supplied
by the flesh of animals, milk and eggs, with a due proportion of
non-nitrogenous food; sheep and oxen work up indigestible vegetable
materials into easily assimilable mutton and beef. The greater
convenience of animal food as a supply of proteid is shown by the
following examples of foods _after the removal of water_:—

  100 parts of rice            contain  7 parts of proteid.
        „      wheat             „     16   „         „
        „      pea flour         „     27   „         „
        „      fat beef          „     51   „         „
        „      dried lean beef   „     89   „         „

On the other hand, vegetable foods are a cheaper source, not only
of carbohydrates and fats, but also of proteids as well. Thus the
approximate cost of—

  1 lb. of proteid in beef is 2s. 8d.
     „        „       milk is 2s. 2d.
     „        „       bread is 1s. 6d.
     „        „       oatmeal is 7½d.
     „        „       peas is 7d.

Under the ordinary conditions of town life, there is considerable
danger of indulging in an excess of nitrogenous food, and vegetarians
may therefore do good by showing that meat is not absolutely necessary,
and can often with advantage be largely replaced by vegetable food.

If we include milk, cheese, and eggs in the vegetarian diet, the
objections to it partially disappear; and it would be well if it were
much more widely known, especially among the poor, that on these,
together with vegetables, health can be maintained with the addition of
little or no meat.

=The Determination of Diet.=—The first principle in making a dietary
is that it =must be mixed=, containing all the necessary constituents,
proteids, hydrocarbons, carbohydrates, water, and salts. No one
of these alone will support life for any considerable period.
Carbohydrates (sugar and starch) can be most easily dispensed with;
fats, on the other hand, are essential for the maintenance of health.

The next point is to ascertain =the proportion= in which these
different foods are required. _Salts_ are commonly taken with other
foods, common salt being the only one taken alone. The amount required
is given on p. 7. The amount of _water_ required varies with the
season of the year, the amount of exercise and perspiration, and other
factors. As a rule, not more than two pints of water are required per
day, and still less if fruit is freely taken. We may therefore confine
our attention to the carbonaceous and nitrogenous foods, and try to
ascertain the amount of each of these required. Every diet must be
subjected to the following tests, to fully ascertain its value:—

1. =The Chemical Test.=—The metabolism undergone by food in the body
being essentially a process of oxidation (though partially modified
and incomplete), the amount of heat yielded on complete combustion of
a food may be taken as a measure of its value as a source of energy,
of which heat and work are convertible forms. The standard of heat
production is the =calorie=, the amount of heat required to raise the
temperature of one gramme of water 1° C. This is the small calorie.
The kilo-calorie (called the =Calorie=) is the amount of heat required
to raise 1 kilo (1 litre) of water 1° C., or 1 lb. of water 4° F. In
calculations on this basis, allowance must be made for foods which are
incompletely oxidised in the body. Rubner has shown that the heat value
of 1 gramme (=15½ grains) of each of the chief food stuffs is as

  Proteid         4.1 Calories.
  Carbohydrates   4.1    „
  Fat             9.3    „

The method of applying this standard to a food is as follows: the
percentage of proteid or carbohydrate given in the following table is
multiplied by 4.1, and the percentage of fat by 9.3:—

  │                            │               IN 100 PARTS.              │
  │                            ├──────┬────────────┬─────┬────────┬───────┤
  │                            │WATER.│ALBUMINATES │FATS.│ CARBO─ │ SALTS.│
  │                            │      │OR PROTEIDS.│     │HYDRATES│       │
  │_Uncooked meat with little  │      │            │     │       │        │
  │  fat_                      │ 74.4 │    20.5    │ 3.5 │   ─   │   1.6  │
  │_Cooked meat─without loss_  │ 54   │    27.6    │15.45│   ─   │   2.95 │
  │_Salt beef_                 │ 49.1 │    29.6    │ 0.2 │   ─   │  21.0  │
  │_White fish_                │ 78.0 │    18.1    │ 2.9 │   ─   │   1.0  │
  │_Bread, white wheaten_      │ 40.  │     8.     │ 1.5 │  49.2 │   1.3  │
  │_Wheat flour_               │ 15.  │    11.     │ 2.  │  70.3 │   1.7  │
  │_Rice_                      │ 10   │     5      │  .8 │  83.2 │   0.5  │
  │_Oatmeal_                   │ 15   │    12.6    │ 5.6 │  63.0 │   3.   │
  │_Peas (dry)_                │ 15   │    22      │ 2.  │  53.  │   2.4  │
  │_Potatoes_                  │ 74   │     1.5    │  .1 │  23.4 │   1.   │
  │_Butter_                    │  8   │     2.     │88   │   ─   │variable│
  │_Eggs (including shell, for │      │            │     │       │        │
  │ which deduct 10 per cent.)_│ 73.5 │    13.5    │11.6 │       │   1    │
  │_Cheese_                    │ 36.8 │    33.5    │24.3 │   ─   │   5.4  │
  │_Milk_                      │ 87.0 │     4.     │ 3.5 │   4.8 │    .7  │

Thus for bread—

  Proteid                          8  ×  4.1  =  32.8
  Fat                            1.5  ×  9.3  =  13.95
  Carbohydrate                  49.2  ×  4.1  = 201.72
  Total Caloric value of 100 grammes of bread = 248.47

The total fuel value in Calories of one pound of certain typical foods
is given by Hutchison as follows:—Butter 3,577, peas 1,473, cheese
1,303, bread 1,128, eggs 739, beef 623, potatoes 369, milk 322, fish
(cod) 315, apples 238.

2. =The Physiological Test.=—Not only is a proper proportion of
proteid, fat, and carbohydrates required, but these must be capable
of digestion and absorption and of oxidation in the body. Cheese is a
highly concentrated food, but its value is less than its percentage
composition would indicate, because of the difficulty of digesting
considerable quantities of it. Green vegetables consist largely of
cellulose, which is only imperfectly capable of absorption into the
blood, although it can experimentally be oxidised by combustion. The
proportion between absorbed food and food rejected in the fæces can
be ascertained by analysis. Many experiments made on these lines show
that on a purely animal diet (meat, eggs, milk) but little nitrogen is
lost, while with vegetable foods (carrots, potatoes, peas, etc.) the
waste of nitrogen is considerable. Fats are very completely absorbed
from the alimentary canal. The amount remaining unabsorbed is greatest
with mutton fat (10 per cent.), least with butter (2½ per cent.).
Experimentally it has been found that an amount up to 150 grammes
(about 5½ oz.) of fat can be absorbed without appreciable loss.
Carbohydrates are very completely absorbed, even starchy foods rarely
escaping digestion. Completeness of absorption from the alimentary
canal is not desirable for all foods; a certain amount of unabsorbed
residue is required to stimulate peristalsis. With a purely vegetable
diet this amount is excessive, and there is physiological waste of

3. In practical dietetics =the Economic test= is important.
Carbohydrate is by far the cheapest food, and generally vegetable
are cheaper than animal foods. Thus a shilling’s-worth of bread
yields 10,764 Calories, while the same sum spent on milk would only
yield 1∕3, and on beef 1∕10 this number of heat units. Similarly a
shilling’s-worth of peas contains 572 grammes of proteid, about double
as much as the same money’s-worth of cheese; while to obtain the same
amount of proteid from eggs would cost more than eight, and from beef
more than five times as much as from peas (Hutchison). The market
price of foods is no certain indication of their nutritive value. Thus
haddock will supply as much nutriment as sole at a fourth of the cost;
Dutch as much nutriment as Stilton cheese at less than half the cost.
Similarly the most economical fats are margarine and dripping.

4. =An Examination of Actual Dietaries= under various conditions has
strikingly confirmed the results obtained by other methods. It has
been found that (_a_) the _potential energy_ required by a healthy man
weighing 11 stones, and doing a moderate amount of muscular work is
3,000 to 3,500 Calories (=310 grains); and that (_b_) about 20 grammes
of nitrogen and 320 grammes (=4,960 grains) of carbon are excreted
by such a man. (_c_) Expressing the 3,000 Calories required in terms
of grammes of food, it is found that 125 grammes of proteid, 500 of
carbohydrate and 50 of fat are necessary. These facts are expressed in
the following table (Hutchison):—

  │              │STANDARD AMOUNT OF│   SAME AMOUNT OF  │               │
  │              │REQUIRED          ├─────────┬─────────┤ IN CALORIES.  │
  │              │(IN GRAMMES).     │ CARBON. │NITROGEN.│               │
  │              ├──────────────────┼─────────┼─────────┼───────────────┤
  │_Proteid_     │       125        │    62   │    20   │       512·5   │
  │_Fat_         │       500        │   200   │    ──   │      2050·    │
  │_Carbohydrate_│        50        │    38   │    ──   │       465·    │
  │              ├──────────────────┼─────────┼─────────┼───────────────┤
  │              │       675        │   300   │    20   │      3027·5   │

Three of the best known standard dietaries give the amounts in grammes
of each food constituent as follows:──

  │              │  PLAYFAIR.  │ MOLESCHOTT. │   ATWATER.  │   AVERAGE. │
  │              ├─────────────┼─────────────┼─────────────┼────────────┤
  │_Proteid_     │     119     │     130     │     125     │     125    │
  │_Fat_         │      51     │      40     │     125     │      72    │
  │_Carbohydrate_│     531     │     550     │     450     │     510    │
  │Calories      │    3140     │    3160     │    3520     │    3273    │

Expressing the same facts in English ounces instead of grammes, 4-2∕5
oz. of proteid, 2½ oz. of fat, and 18 oz. of carbohydrate, would
represent the ounces of each constituent required according to

                              (1)              (2)
  │                    │AVERAGE OF ABOVE│   HUTCHISON.   │
  │                    │THREE DIETARIES.│                │
  │                    ├────────────────┼────────────────┤
  │_Proteid_           │      4-2∕5     │      4-2∕5     │
  │_Fat_               │      2-1∕2     │      1-4∕5     │
  │_Carbohydrate_      │     18         │     17-3∕5     │
  │_Ounces of dry food_│     24-9∕10    │     23-4∕5     │

The chief point of divergence in the above standard dietaries is in
the relative proportion of carbohydrate and fat. Probably the correct
proportion between these is as 1 to 10; but it will vary according to
climate and other circumstances. Detailed examination of a large number
of dietaries shows that the amount of daily proteid should be about
125 grammes, or 4-2∕5 ozs. This is contained in 20 eggs, or in 18 oz.
_i.e._ about 4½ ordinary platesful of cooked meat.

It must be noted that the 23-24 oz. of food given above as the standard
daily amount represents dry food. This represents 40 oz. or nearly 3
lbs. of ordinary food.

The following example by Waller, gives a rather liberal standard
English diet, for a man doing a moderate amount of muscular work.

                                       CARBON.   NITROGEN.

  _Foundation_:  1 lb. bread             117        5.5
                 1∕2 lb. meat             34        7.5
                 1∕4 lb. meat             84         —

  _Accessories_: 1 lb. potatoes           45        1.3
                 1∕2 pint milk            20        1.7
                 1∕4 lb. eggs             15        2.0
                 1∕8 lb. cheese           20        3.0
                                         ———       ————
                         Total           335       21 grammes.

This divided up into meals works out roughly as follows (Hutchison):—

             {Two slices of thick bread and butter.
  Breakfast  {Two eggs.

             {One plateful of potato soup.
  Dinner     {A large helping of meat with some fat.
             {Four moderate sized potatoes.
             {One slice of thick bread and butter.

  Tea         A glass of milk and two slices of thick bread and butter.

  Supper      Two slices of thick bread and butter and 2 oz. of cheese.

From the preceding data, practical problems as to dietaries are easily
solved. Thus if it be required to find

 _how much oatmeal, milk, and butter would be required to give a
 sufficient quantity of albuminoids, fats, and carbohydrates to an
 adult male_,

the calculation may be based on the figures in the table on p. 32, or
the following figures may, for the sake of convenient calculation, be
taken as representing the percentage amount of each of these chief food
principles contained in the foods named:—


  Oatmeal        12           6           60
  Milk            4           3            5
  Butter          2          88           —

  Let o = number of ounces of oatmeal required.
      m =   „         „       milk      „
      b =   „         „       butter    „

  Then  (12o + 4m + 2b)∕100 = 4.5 ozs. of albuminoid

        (6o + 3m + 88b)∕100 = 3 ozs. of fat

               (60o + 5m)/100 = 14.25 ozs. of carbohydrate,

according to Moleschott’s diet.

When these equations are worked out by substitution and transference—

  o = 19.2 ounces.
  m = 55.4   „
  b = 0.24   „

 _Similarly if it is required to find how much meat, bread, and butter
 of the following percentage composition will be required to give a man
 a sufficient amount of albuminoids, fats, and carbohydrates._

  Meat         25          15            0
  Bread         8           1.5         50
  Butter        2          88            0

  Let m = number of ounces of meat required.
      b =   „         „       bread   „
      B =   „         „       butter  „

  Then      12m + 8b + 2B/100 = 4.5 ozs. of albuminoid

         (15m + 1.5b + 88B)/100 = 3 ozs. of fat

                      50b/100 = 14.25 ozs. of carbohydrates

 When these equations are worked out—

  m = 6.28 ounces.
  b = 28.5   „
  B = 1.15   „

=Relation of Food to Mechanical Work.=—In the body the movements of
every part are constant sources of heat. It is evident therefore that
the potential energy of food can be expressed by (_a_) the amount of
heat obtained by its complete combustion, or (_b_) by the amount of
work capable of being obtained from it. Joule discovered by exact
experiment that the mechanical power obtainable from a given amount
of fuel is directly proportional to the amount of fuel used, being
in fact due to the oxidation of this fuel, the heat produced being
transformed into mechanical power. The _heat unit_ or calorie has been
already given (p. 32). The gram-metre is the _work unit_. The heat unit
corresponds to 425.5 units of work. Thus the same energy required to
heat one gramme of water 1° C. will raise a weight of 425.5 grammes to
the height of 1 metre. Conversely a weight of 425 grammes if allowed
to fall from a height of 1 metre, will by its concussion produce heat
sufficing to raise the temperature of 1 gramme of water 1° C. In
England the amount of work done is commonly expressed as foot tons,
_i.e._ tons lifted one foot; while in France it is similarly expressed
as kilogrammetres. Gramme-metres can be converted into foot-pounds
by multiplying them by .007233, and kilogrammetres into foot-tons by
dividing by 311.

Frankland estimated that—

  1 oz. dry albumin        yields 174 foot-tons of potential energy.
  1 oz. fat                  „    378     „              „
  1 oz. starch               „    135     „              „
  1 oz. cane sugar           „    129     „              „
  1 oz. glucose or lactose   „    122     „              „

In practical dietetics digestibility of food as well as chemical
composition is an important factor. Furthermore metabolism in the body
is not in every instance so complete as oxidation outside it. Hence
estimates of potential energy can only be regarded as theoretically
correct. Examination questions like the following are occasionally

 A man does work equal to 176.8 foot-tons in a day. Supposing that he
 eats only bread, how much will he require to give the amount of energy
 required, if bread contains 8 per cent. proteid, 1.5 per cent. fat,
 and 49.2 per cent. carbohydrate?

 On the above basis, from 100 ounces of bread the amount of potential
 energy obtainable is:—

       8 × 174 = 1,392 foot-tons
     1.5 × 378 =   567     „
    49.2 × 135 = 6,642     „
  Total energy = 8,601     „     obtained from 100 ozs. bread.

 Let _b_ = number of ounces of bread required to develop 176.8
 foot-tons of energy.

 Then 8,601: 100:: 176.8: _b_.

 Therefore _b_ = +2.05 ounces+.



OBJECTS OF COOKING.—Food may be taken in its crude condition, as
directly derived from the animal or vegetable world, or after it has
undergone a preparatory process of cooking. Man is the only animal
who cooks his food. Many foods, in the uncooked condition are almost
entirely incapable of digestion by him—such as the proteid and
farinaceous materials contained in the seeds of cereal and leguminous
plants. But cooking, as a preparatory help to the digestion of food,
is not equally required by all foods. Thus, fruit is commonly taken
uncooked, and does not undergo any important alteration on cooking.
Salads are taken uncooked, but not for their nutritive properties so
much as for a relish to other foods, and for their quasi-medicinal
properties. Milk, again, may be taken cooked or uncooked. The oyster
is the only animal which is eaten habitually, and by preference, in
the uncooked condition; and there is a physiological reason for this
universal custom. The large fawn-coloured liver, which constitutes
the delicacy of the oyster, is little else than glycogen, associated
with its appropriate ferment diastase, so that the oyster is almost
self-digestive. When cooked, the ferment is destroyed, and digestion of
the oyster becomes more difficult.

Cooking is intended—1. _To make the food softer_, and in part to
mechanically disintegrate it, thus rendering it more easily masticated
and digested. In fact, cooking, in the best sense, is an artificial
help to digestion; and digestion may well be said to commence in the

2. _To produce certain chemical changes._ Thus, starch is partially
converted into dextrine; gelatin is formed from connective tissue, etc.

3. _To destroy any noxious parasites_ present in the food, or obviate
any ill effects from _putrefactive changes_. Diseased meat chiefly
produces bad effects when imperfectly cooked.

4. _To make the food more pleasant_ to the eye and agreeable to the
palate. The improved savour in cooked meat, for instance, has a very
appetising effect, and consequently makes digestion easier.

THE COOKING OF FLESH.—1. =Roasting= is, perhaps, the most perfect way
of cooking meat. It exalts its flavour more than any other method. In
roasting, place the meat at first sufficiently near a brisk fire, so
that the albumin on its surface may be readily coagulated, and the
juices retained in the interior of the joint. After about fifteen
minutes, the joint ought to be removed somewhat further from the fire,
and allowed to cook slowly. Frequent basting is desirable to obtain a
good result. Brown meats, such as beef, mutton, and goose, require a
quarter of an hour per pound weight; veal and pork require about ten
minutes additional, to ensure the absence of redness. White-fleshed
birds require a somewhat shorter time. The time required in roasting
will be a little more if the joint is large, or the fire not very
clear. To ascertain if the meat is sufficiently cooked, press the
fleshy part; if it remains depressed, it is done; if not done, it
retains its elasticity. At the first incision, gravy should flow out of
a reddish colour.

_The changes undergone_ during roasting are, that the connective
tissues uniting the muscular fibres is converted by the gradual heat
into gelatin, which is soluble and easily digested; the muscular
fibres, consequently, become more separable, and the myosin of which
they consist is rendered more digestible. The fat is partly melted
out of its fat cells, and partly combines with the alkali from the
blood-serum. Empyreumatic oils (_i.e._ fat partially burnt), developed
by charring of the surface of the joint, are carried off when it is
roasted in front of the fire; and so, to a large extent, is acrolein.
Acrolein (C₃H₄O) is always produced by the destructive distillation of
neutral fats containing glycerine, and is the cause of the intolerably
pungent odour accompanying the process. Osmazome, a peculiar extractive
matter, on which the flavour and odour of meat depend, is developed
better by roasting than by any other method of cooking.

It is useful to remember, in buying beef or mutton, that 20 per cent.
must be allowed for bone and 20 to 30 per cent. for the loss during

The following figures are by Johnston:

                                   IN ROASTING.  IN BAKING.  IN BOILING.
  4 lb. of mutton lose in weight   1 lb. 6 oz.   1 lb. 4 oz.    14 oz.
    „      beef    „        „      1 lb. 5 oz.   1 lb. 3 oz.     1 lb.

Thus roasting is the least economical method of cooking. The chief
loss, however, is of water; the dripping and gravy are recoverable.

2. =Baking= of meat in a closed oven does not produce so agreeable a
result as roasting in front of an open fire. The oven ought always to
be very hot before the meat is put in, in order to rapidly coagulate
its surface. Baked meat may have an unpleasant flavour, owing to its
saturation with empyreumatic oils, which escape in open roasting. The
unpleasant flavour can be prevented by covering the meat with a layer
of some non-conducting material, as a pie-dish or a crust, no empyreuma
being then formed. Baked white of egg, as in the dish of fried ham and
eggs, is one of the most indigestible forms of albumin obtainable.

3. =Boiling= of meat requires the same time as roasting. If the flavour
and juices are to be retained, the joint ought first to be plunged into
soft boiling water, and then, after three minutes, allowed to stand
aside in water at 170° Fahr. The preliminary boiling forms a coating
of coagulated albumin over the joint. Where there is no thermometer
to guide the cooking—after the preliminary boiling for three to five
minutes, add three pints of cold water to each gallon of boiling water,
and retain at the same temperature for the rest of the process, _i.e._,
at about 170° Fahr. If the meat is boiled in an inner vessel surrounded
by water (water-bath), the temperature of the inner vessel does not
rise above 160°-170° F. Ordinary “simmering” means that the meat is
kept all the time at a temperature of 212° F. and is thus spoilt. The
boiling of an egg is an example of the same point. If an egg is kept in
water at a temperature of 170° F. for 10 to 15 minutes, its contents
form a tender jelly, while an egg kept in water at 212° F. for the same
length of time is hard and tough. An egg is more digestible when cooked
in water at 170° F. for 10 minutes than when boiled in water for 2½

The use of soft water for cooking purposes is always advisable;
otherwise a longer period must be allowed. A preliminary boiling for
a few minutes renders hard water softer, and the addition of a little
carbonate of soda has a like effect.

When meat is inserted in water at a temperature below its boiling
point, the juices are gradually extracted, while the meat is left a
mass of indigestible fibres. A good soup is produced, but the meat is
almost valueless. In order that the soups and broths may be nutritious,
the less heat is employed in their preparation the better. If a soup is
strained to make it clear, much of the most valuable part is removed.

=Stewing= is a process intermediate between boiling and baking. It
possesses the great advantage over dry baking that no empyreumatic
gases are produced, and there is no charring. The temperature of the
stew-pan ought never to be above 180° Fahr.; at this heat the roughest
and coarsest kinds of meat are made tender. The only objection to
stewing is that the meat becomes saturated with fat and gravy, and is
too rich for weak stomachs. It is advisable to stew lean meats only.

=Hashing= is a process of stewing applied to meat which has been
previously cooked. The consequence of this double cooking, is that the
meat becomes tough and leathery. A modified hash in which the meat is
simply well warmed throughout is preferable.

=Frying=, unless carefully done, renders meat difficult of digestion,
each fibre becoming coated with fat. The art is to “fry lightly,” that
is, to burn quickly and evenly, so that no charring is produced. Two
methods of frying are described. In the first, the substance to be
fried, as an omelette or pancake, is placed with a little fat or oil
in a frying-pan. This is really a modified process of roasting, the
fat merely serving to prevent the object from adhering to the shallow
pan. In the second, the substance to be fried is immersed in fat; for
this purpose a frying kettle is required. Olive oil or good cotton
seed oil is best for use in the frying-kettle. Lard is a bad material
for frying; both it and butter are apt to burn unless heated slowly.
Dripping is a good substance for frying. The fat used must be heated
to from 350° to 390° F., and then the substance to be fried, _e.g._
a sole, plunged into it and left for two or three minutes. In this
process the substance of the sole is really being steamed by the steam
generated in the substance of the sole.

6. =Broiling and Grilling= are really processes of roasting applied to
small portions of meat. In grilling, it is important that the gridiron
should be hot before putting anything on it. An external coagulation of
albumin is produced, as in good roasting and boiling.

THE COOKING OF MIXED DISHES.—A few instances may be given of common
errors in preparing compound dishes. An egg in a custard, or just
coagulated in a poached egg, is a light and easily-digested food; baked
half an hour in a pudding, it is much less digestible; fried with ham,
it is almost as indigestible as leather. Spices, if mixed with a dish
before it is boiled, lose nearly all their flavouring power, while they
remain irritating. They ought to be added near the end of the cooking
process. A soup containing vegetables, as well as meat juices, should
be prepared in two parts. The vegetables require prolonged boiling;
gravy is spoilt by this. Similarly, the jam in a tartlet, if inserted
before baking, loses its proper fruity flavour; and oysters baked in a
beef-steak pie are indigestible.

THE COOKING OF VEGETABLE FOODS.—=Bread= is either vesiculated or
unvesiculated; the latter being what is called unleavened bread.
Vesiculation of bread has usually been produced by _fermentation_
of some of the sugar of the flour. The starch first becomes sugar
(dextrose) and then the growth of the yeast plant in the dough
splits this up into alcohol and carbonic acid gas. The carbonic acid
percolates the substance of the dough, rendering it porous. When it has
“risen” sufficiently, the dough is placed in the oven. The heat of the
latter kills the yeast plant, thus preventing any further fermentation,
but at the same time expands the carbonic acid gas in the bread,
rendering the latter still more porous, and drives off in a gaseous
condition the greater part of the alcohol produced by the previous

It is objected to this plan of making bread, that a little of the
sugar is wasted in producing alcohol and carbonic acid. To remedy
this, _another plan_ is sometimes adopted, as first proposed by _Dr.
Dauglish_. In it the dough is charged with carbonic acid dissolved in
water under considerable pressure. The gas escapes in the substance of
the dough, and on baking expands as in the ordinary method of making
bread. Bread made in this manner, is called “aerated bread.” Nevill’s
bread has a solution of carbonate of ammonia incorporated in the dough,
which is dissipated by heat, thus causing vesiculation of the bread.

On the continent, a mixture of hydrochloric acid and carbonate of soda
is commonly used, carbonic acid and common salt being formed in the
dough. Thus NaHCO₃ + HCl = NaCl + H₂O + CO₂. The hydrochloric acid
employed should be perfectly pure and free from arsenic. Baking powders
are also largely used for making cakes. “Self-raising” flour is flour
with which baking-powder has already been mixed. Most baking-powders
consist of a mixture of carbonate of soda and tartaric acid or
bitartrate of potash, diluted with starch. When wetted, carbonic acid
gas is evolved. A few contain alum, which is now an illegal material
for this purpose.

Ten pounds of flour ought to make thirteen to fourteen of bread.
The use of stale bread is much more economical than of newly-made
bread; besides this, it is more digestible. Newly-made bread is more
palatable than stale, but it is more cohesive, and does not crumble
into separate particles like stale bread. The consequence is, that it
is less digestible, being less easily penetrated by the saliva and
other digestive juices. The effect of _toasting_ is to render bread
more friable, and consequently more digestible. It ought, however, to
be thin and eaten soon after it is made; when thick and kept too long,
it becomes tough and leathery.

=Pastry= is less easily digested than ordinary bread. The lard or
dripping added renders it more flaky and less easily pulverised; and,
in addition, the fat coats over the starch cells; and thus the action
of the digestive juices on the pastry is impeded.

=Potatoes= ought to be boiled in their jackets, or steamed, to avoid
loss of nitrogenous material and salts. Moist heat causes the starch
granules to swell, and ultimately softens and bursts the cellulose
envelopes in which these are contained. Dry heat, as when potatoes
are baked, converts starch into a soluble form, and ultimately into
dextrine (= C₆H₁₀O₅), an intermediate stage towards the formation of
dextrose (_i.e._ glucose = C₆H₁₂O₆).

=Peas and Beans= ought to be boiled slowly and for a long time to
render them more digestible. If old, they ought to be soaked in cold
water for twenty-four hours, then crushed, and stewed. Hard water
must be avoided in the cooking of peas and beans as well as of other
vegetables, as the lime-salts form insoluble compounds with legumin.

=Green vegetables= require thorough and prolonged cooking. This renders
their tissues softer and more easily attacked in digestion. The members
of the cabbage tribe and carrots can hardly be boiled too long. Soft
water ought always to be used; this is one reason why steaming is
preferable. Before boiling, all vegetables should be well washed in
cold water. A little vinegar will remove any insects present.

COOKING APPARATUS.—The apparatus required in cooking may be divided
into kitchen utensils and cooking ranges.

To ensure good cooking, perfect cleanliness of all apparatus is
indispensable. The use of the frying-pan, gridiron, spit, and oven has
been sufficiently indicated under the description of the different
methods of cooking. The form of stove to be used for cooking meat is
gradually being settled against the old open stove. Although this
secures a somewhat more savoury joint than when meat is baked, it is
extravagant in working. The closed kitchener in which coal is employed
is less economical than a gas stove at the present price of gas, if the
latter is carefully used.

Various appliances for economising fuel have been devised, and at the
same time of allowing of the prolonged action of a moderate degree of
heat. These are usually constructed on the principle of an ordinary
bath, consisting of a double pan, with a layer of water between the
two compartments. Warren’s cooking-pot belongs to this type. The
Aladdin oven consists of an iron box with an opening above to let
off superfluous steam. This box is surrounded by another composed of
non-conducting material, while a lamp below furnishes the heat. Dr.
Atkinson has calculated that in an ordinary oven 2 lbs. of fuel must
be expended for every pound of food cooked, while in his Aladdin oven
2½ lbs. of fuel will cook 60 lbs. of food. Time is an important
element in cooking. Food is most thoroughly cooked and most digestible
when subjected to a temperature below that of boiling water for a
prolonged period.

THE PRESERVATION OF FOOD.—All organic foods tend rapidly to decompose
and putrefy. Putrefaction only occurs when a warm and moist substance
is exposed to the air. The problem of preserving any food, therefore,
may be solved (1) by keeping it at a very low temperature, (2) by
desiccating it, or (3) by boiling or steaming it so as to destroy any
microbes in the food which would otherwise start putrefaction, and then
fastening it in an air-tight case.

Milk is commonly preserved as condensed milk, and in this condition
is very valuable. A pure condensed milk is now supplied, prepared
without the addition of sugar or any antiseptic, but in which, as in
other condensed milks, all disease-producing or decomposition-producing
microbes have been destroyed during the process of concentration. Milk
may also be desiccated; in this condition it is difficult of digestion.

In addition to the household methods of preserving fruits, large
quantities of fruits—both moist and dry—are now imported, protected
by syrup or sugar, in sealed canisters; and they retain the original
flavour almost unchanged.

The preservation of meat is effected by—

1. =Drying.=—This must be done rapidly. It is a process which is best
applicable to fish, but has been applied also to beef. Dried Hamburg
beef is used for making sausages. Pemmican, largely used by Arctic
voyagers, consists of a mixture of meat and fat, dried and powdered
along with some spices; it is generally eaten with some kind of meal.

2. =Cold.=—Frozen meat now forms a very large part of the food of
the English people. If the meat has been frozen before rigor mortis
(rigidity after death) has commenced, it keeps well; if frozen later,
it rapidly decomposes after being thawed. Freezing arrests putrefaction
and tends to conceal its odour. Hence the bad condition of frozen fish
may not be detected until it is cooked. In cooking frozen meat, time
should be allowed for thawing to occur, before the meat is placed in
the oven. Much of the ill-founded prejudice against frozen meat arises
from inattention to this point. Frozen meat is equal in nutritive value
to and does not lose more in cooking than fresh meat.

3. =Salting= may be done with brine or saltpetre (nitrate of
potassium); the latter does not decolourize the meat like the former.
Salted meats have lost much of their nutritive material, in the
form of albumin and salts, and the remaining meat is harder and more
difficult of digestion than fresh meat.

4. =Immersion in antiseptic liquids= or gases, as sulphite of soda,
is objectionable, on account of the addition of extraneous, and not
altogether innocuous, salts. Boric acid powder is largely used for
sprinkling on meat, particularly rabbits, etc., and for preserving hams
and other meats. Its use is to be deprecated. All such meats should be
thoroughly washed with water, before being cooked.

Solutions of _boric acid and borax_ are frequently added to milk. Their
use is objectionable (_a_) because they tend to conceal incipient
decomposition, but do not prevent its possible evil effects, and (_b_)
because they enable the farmer to palm off dirty milk on the public.
Were the addition of preservatives to milk forbidden, the farmer could
perfectly well keep his milk sweet until it reached the town-consumer
by adopting strict measures of cleanliness, and by cooling his milk
before it leaves the farm. At the least it should be made obligatory on
the milk retailer to declare the presence of preservatives in milk sold
by him.

 The presence of borax or boric acid can be detected by evaporating
 the milk to dryness, incinerating and then moistening the ash with a
 drop of strong sulphuric acid. If a little alcohol be now added, on
 applying a light, a green flame indicates boric acid. Milk or cream
 containing boric acid turns blue litmus paper red.

_Formalin_ is also sometimes used as a preservative for milk in very
weak solution.

 Its presence can be determined by diluting the milk with water in a
 test-tube, and running strong sulphuric acid down the side of the
 tube, taking care to prevent mixing. At the junction of the acid and
 diluted milk a violet ring is seen if formalin is present.

_Salicylic acid_ was formerly used as a milk preservative, but is now
seldom used except in beers. All these preservatives are objectionable
in milk, although their injurious action may be difficult to prove.

5. =Coating with fat or gelatine= has only succeeded in conjunction
with the exclusion of air. This process is especially applicable to
fishes, as tinned sardines. In a modified form, it is useful in coating
potted meats, etc.

6. =Heating and Air-tight Cases.=—Tinned meats prepared according
to this method are imported in large quantities. In the process of
preparation, the cases are packed with meat and filled up with gravy,
and then closed with a cover which is hermetically sealed, except at
one point. The case is then heated to 250° Fahr., in order to drive
out all air, and destroy any putrefactive germs present. The open
point is sealed while the gravy is still boiling, thus making the case
completely air-tight. Albumin is coagulated at about 170° Fahr.; the
higher temperature, which it is found necessary to employ, overcooks
the meat and renders it less digestible (see also p. 40).



CONDIMENTS, ETC.—The name condiment is used in various senses by
different writers. In its strictest sense it is a substance containing
a volatile oil or ether, which may be taken with salt, and the object
of which is to excite the senses of taste and smell, and consequently
produce an appetising effect. This definition excludes _spices_,
substances allied to condiments, but usually taken with sugar, as
cinnamon, ginger, etc.; also _flavouring agents_, such as vanilla;
and _acids_, such as vinegar and lemon-juice. If we use the word in
its widest sense, to include these various groups of substances, we
find that all condiments are taken with the object of improving the
taste or flavour of food, or of assisting its digestion; but that they
are not foods in the sense of supplying any elements towards building
up the body or maintaining its heat. The only partial exception is
lemon-juice, the salts of which have a quasi-medicinal use.

Taste is usually a compound sensation, the organs of which are the
nerves of taste and smell. True taste is confined to the appreciation
of sensations of bitter and sweet; but the flavour of meats is nearly
entirely appreciated by the sense of smell. This is shown by the fact
that meats appear tasteless and insipid, during “a cold in the head.”
In the appreciation of acid, astringent, and fiery substances, the
sense of touch is also employed. The excitement of these different
nerves results in a stimulus which is carried up to the central
nervous system, and causes by reflex action an increased flow of the
digestive juices. Hot substances, like cayenne and ginger, also cause
an increased flow of gastric juice, by directly congesting the mucous
membrane. This action is not so desirable as that through the influence
of the nervous system. All natural foods are sapid and possessed of
flavour, and thus stimulate secretion; but any local irritating effect
ought to be avoided.

1. =Condiments= proper comprise chiefly mustard, pepper, cayenne,
garlic, onion, capers, mint, sage, morels, mushrooms, truffles. The
last three on the list are also foods, but are more commonly used as

All these act as stimulants to the digestive organs, and in small
quantities aid digestion. The active principle of mustard and
horse-radish is sulphocyanide of allyl. Horse-radish is not so
wholesome as mustard, the scraped root being apt to adhere to the
stomach like the skins of grapes, and produce indigestion. Pepper
contains an acrid resin, a volatile oil, and an alkaloidal substance,
called piperine. Cayenne contains an analogous substance, called
capsicin. Cayenne, unless in extreme moderation, is harmful, as its
small particles adhere to the mucous membrane of the stomach, and may
set up considerable irritation.

2. =Spices= are those condiments which contain an aromatic oil, and
which harmonize with sugar. They are, as a rule, less irritating to
the stomach than those of the pepper group. Cinnamon, cloves, camphor,
ginger, and curry powder are the chief of these. Curry powder really
belongs to both the first and second divisions. When genuine, it is
said to contain turmeric, cardamoms, ginger, allspice, cloves, black
pepper, coriander, cayenne, and a few other substances.

3. =Flavouring agents=, such as vanilla, lemon peel, and fruit
essences, are used to give a pleasant flavour to various dishes.

4. =Acidulous substances= are taken chiefly because of their sharp and
agreeable taste. Vinegar is the chief acid employed. It is produced
by the action of a fungus (_Mycoderma aceti_) on alcoholic liquids,
as wine, or beer, C₂H₅OH (alcohol) becoming C₂H₄O₂ (acetic acid). It
is also produced by the destructive distillation of wood. In small
quantities it does not stop digestion, but, by exciting the nerves
of taste, may be of actual service. It helps to soften the vegetable
fibres in a salad; and is also useful for the same purpose with hard
meats, as lobster, etc. In large quantities it diminishes the power to
assimilate food.

 Good vinegar ought not to contain less than 3 per cent. of acetic
 acid; and sulphuric acid beyond 1 in 1000 in vinegar is to be regarded
 as an adulteration. A specific gravity below 1015 indicates the
 addition of water.

Citric acid and lemon-juice are useful for their refreshing properties,
and the latter also because of its alkaline salts.

=Oils=, such as olive oil, have been sometimes classed under
condiments, but as they have great nutritive properties, this is hardly
accurate. For the same reason, =salt= is not classed under this head.


Water is the universal beverage, and for healthy persons is preferable
to any other. All other beverages necessarily contain it as their basis.

It will be convenient to consider first aërated and other natural
waters; then tea, coffee, and cocoa; and finally, alcohol.

=1. Aerated Waters= contain carbonic acid (carbon dioxide) in solution,
which gives to them their characteristic sharp taste and sparkling
character. Thus distilled water charged with gas is sold as Salutaris
or Puralis water. Soda water contains three to five grains, and
medicinal soda water fifteen grains of bicarbonate of soda to the
bottle. Potash water contains fifteen grains of bicarbonate of potash
to the pint, in each case carbonic acid being dissolved under pressure.
In lemonade, ginger-beer, etc., the basis is sweetened water, rendered
tart by the addition of an acid, and finally charged with carbonic
acid. Lemonade frequently contains acetic or phosphoric acid instead
of citric or tartaric, and ginger-beer the same constituents with some
added tincture of ginger. Home-made lemonade prepared from fresh lemons
is a much more wholesome drink. Ginger-beer (stone ginger) is produced
by the fermentative action of yeast on a solution containing sugar,
bruised ginger, tartaric acid, and oil of lemon. It usually contains at
least two per cent. of alcohol.

=Natural Mineral Waters= usually contain common salt (chloride of
sodium) and alkaline salts of soda or lime, and are impregnated with
carbonic acid gas. Apollinaris, Rosbach, and Johannis possess these
characteristics. The carbonic acid in natural waters is partially
combined, and is given off more gradually than that in artificial
mineral waters.

In all the preceding waters there is considerable carbonic acid.
This acts as a sedative to the mucous membrane of the stomach, and
is useful in indigestion. An aërated water added to milk renders it
more digestible by diluting it, and by preventing the formation in the
stomach of a heavy clot of casein. In the making of artificial aërated
waters, it is essential that the water employed should be pure, that
the acid used in generating the carbonic acid should be free from
arsenic or other impurities, and that the water should not be allowed
to come into contact with lead at any stage, as in pewter fittings. One
per cent. of proof spirit is allowed in temperance beverages by the


Tea is the leaf of an evergreen shrub, the _Camellia thea_, which is
cultivated in China, Japan, British India, Ceylon, Java, and other
countries. The tea leaves, as seen in this country, uncurl in hot
water. They are lanceolated, with a serrated edge, and the veins do
not extend to the edge of each leaf. By these characteristics they
may be distinguished from foreign leaves, _e.g._, the sloe and willow
used as adulterants (Fig. 4). The use of old and exhausted leaves
can be detected by a determination of the percentage of soluble
matter dissolved by boiling water from a given weight of tea. This on
evaporation to dryness should be 28 to 30 per cent. of the total weight
of the original tea. The presence of clay, iron dust or other forms of
dust is detected by igniting a given amount of tea and determining the
amount of ash. This should be only about six per cent.

In _black tea_, the leaves are dried in the sun, rolled and allowed
to become soft and to ferment. During this process, some of the
tannin appears to be converted into less soluble forms. The leaves
are afterwards sun-dried, and these “fired” in a furnace. _Green tea_
leaves are dried in the fresh condition over wood fires. Indian teas
have more “body” and astringency than China teas. The smallest and
topmost leaves of the tea plant give the finest sort of tea (Orange
Pekoe); next to this comes Pekoe; the next largest leaves producing
Souchong; after these Congou; while the coarser leaves nearer the base
used to yield Bohea, which is now seldom seen.

Tea consists of three important constituents—volatile oil, theine or
caffeine, and tannin—and soluble and insoluble extractive matters.

  The amount of caffeine varies from  2 to 4  per cent.
   „    „    „  tannin     „     „   10 to 12  „   „
   „    „    „  volatile oil is about   1∕2    „   „

(1) =Volatile Oil= gives the aroma and flavour to each particular tea.
It is this which causes the headache, trembling, wakefulness, and
restlessness, occasionally produced by tea, especially by green tea.

[Illustration: LEAVES OF

(_a_) ELDER. (_b_) TEA. (_c_) TEA. (_d_) SLOE. (_e_) ELDER.

FIG. 4.]

(2) =Theine= or =caffeine=, is an alkaloidal crystalline principle. Its
composition is represented by the formula C₈H₁₀N₄O₂, H₂O. Ceylon
tea, broken leaf contains 4·03 per cent., Assam (Indian) tea, broken
leaf 4·02 per cent., while Chinese teas contain from 2·89 (Moyune
Gunpowder) to 3·74 (Moning, black leaf) per cent. of caffeine (Allen).

Theine is the most important constituent of tea and coffee. It is a
stimulant, but unlike alcohol, acts even more upon the central nervous
system than upon the heart. It removes the sense of fatigue, and may,
especially if taken in excessive doses, produce sleeplessness. Its
stimulant action on the heart is followed by increased flow of urine,
and it thus helps in the removal of waste products from the system. The
effect on the tissue-changes of the body is somewhat doubtful. It has
been stated to arrest or diminish the waste, _i.e._, the metabolism,
constantly going on in the system, and so diminish the amount of
food required to repair this waste. This is highly improbable; we
cannot conceive the likelihood of the development of energy without a
corresponding expenditure of material, and that is what would be the
case if theine increased the activity of various organs while retarding
their waste. The experiments of Conty and Guimarès on the action of
coffee show that this (and tea has the same essential constituent) does
not diminish tissue waste. It does not prolong life in starvation,
though it may lessen the feeling of hunger. Hence tea and coffee, which
owe their value mainly to the caffeine or theine contained in them, are
in no sense foods.

(3) The amount of _Tannin_ varies from 12·31 in Ceylon tea (broken
leaf, Pekoe) to 11·76 in Moning, black leaf, and 9·9 per cent. in Natal
Pekoe Souchong (Allen). The difference in tannin between Chinese and
Indian teas is not therefore so great as is usually supposed. Tannin
is a powerful astringent, and possesses a bitter styptic taste, and
a constipating effect on the bowels. Its amount is increased by long
“brewing,” as is shown by the following results (Hale White):—

                  _Three Minutes’       _Fifteen Minutes’
                    Infusion._             Infusion._

  Finest Assam    11·30 per cent.         17·73 per cent.
    „    China     7·77  „    „            7·97  „    „
  Common Congou    9·37  „    „           11·15  „    „

=The Mode of Preparation of Tea= is important. It is clear that the
percentage of tannin to weight of leaf used in making the infusion
increases with the protraction of the infusion. On the other hand
caffeine is so soluble that it is nearly completely dissolved as soon
as infusion has begun. Dittmann found that five minutes infusion of
Indian tea extracted 3·63 and ten minutes infusion 3·73 per cent. of
caffeine. The Chinese put the tea leaves in a cup, and having poured
boiling water on them, drink the resulting infusion after a very short
time, without adding anything. The Russians drink the infusion with a
squeeze of lemon, and with or without sugar. We add cream or milk and
generally sugar, and so render it more nutritious, though the delicate
flavour is veiled. The Chinese plan of infusion for a short time is
the best, as it ensures the extraction of the aromatic and stimulant
principles of the tea with only a proportion of the tannin.

In making tea it is important to use a tea-pot which is quite dry, in
order to avoid mustiness; to pour a small quantity of boiling water
into the tea-pot and then out again, so that the infusion may be made
at the temperature of boiling water; and to use water which has only
freshly come to the boil, and so has not been rendered flat, and not
to infuse longer than five minutes. For persons of weak digestion,
the best kind of tea is that obtained by pouring boiling water on
the leaves, and then immediately pouring the resulting infusion
into another hot tea-pot. In all cases where tea has to be kept a
considerable time, it should be poured into a second tea-pot, the
leaves being left behind.

Indigestion is not an uncommon consequence of tea-drinking; caused by
the excess of tannin in the tea, by the other constituents of the tea,
or more commonly by the practice of drinking tea in small sips, with
bread and butter. The tea infusion usurps the place of the saliva, the
secretion of saliva remaining partially in abeyance. The presence of
tannin in tea renders it an undesirable part of a substantial meal.
Tannin coagulates albumin, and retards its solution by the digestive
juices. Hence “high teas” and “tea-dinners,” unless the tea is very
weak, are objectionable. The practice of drinking tea with every meal
is inexcusable.

For quenching thirst during active exercise, and rendering possible
prolonged exertions, tea is unsurpassed.


Coffee is the seed of the berry of the _Caffea Arabica_. Each berry
contains two seeds, or beans as they are sometimes incorrectly called.
The coffee is prepared by roasting the seeds until they assume a
reddish-brown colour, in which process they lose 15 per cent. in weight
and gain 30 per cent. in bulk. During the process of roasting, a
volatile oil having a powerful aromatic smell is developed. This is not
produced in such large quantities from fresh seeds; the best time for
roasting varying, however, for different varieties of coffee.

The amount of =Volatile Oil= in coffee is much less than in tea. As it
is elicited during the process of roasting, this should be done with
nicety and care. It is effected in an iron cylinder made to revolve
over a fire. After the roasting, the sooner the seeds are ground the
better the coffee. When it cannot be immediately used, it should be
kept in closed canisters, and not in paper or open jars.

In addition to the volatile oil, which is contained in roasted
coffee in the proportion of about 1 part in 50,000, coffee contains
=caffeine=, of which there is 3∕4 to 1 per cent., and an =astringent
acid=, called caffeo-tannic or caffeic acid, which differs from
ordinary =tannin= in that it does not blacken a solution of an iron

The chief adulteration of coffee is =Chicory=, which is thought by some
to improve the coffee. It is generally harmless, though in some people
it produces heartburn and diarrhœa. Chicory is prepared from the root
of the wild endive. It contains a volatile oil and a bitter principle,
but no caffeine. It is, therefore, of no utility as a stimulant. Its
presence can be detected by shaking a little of the suspected coffee on
to the surface of the water in a wine-glassful of cold water. Coffee
swims on the surface, and gives little or no colouration to the water;
while chicory sinks, and gives a deep red tint. The aqueous extract of
pure coffee (extracted by boiling water) is, when evaporated, 25 to
30 per cent. of the weight of the original decoction of coffee; while
that of chicory is 65 to 70 per cent.; and on this basis, as well as
on the fact that a filtered decoction of 10 grammes of coffee in 100
c.c. of distilled water, cooled to 60° F. has a specific gravity of
1009, while that of a similar solution of chicory would be 1021,
the proportion of chicory in a mixture of coffee and chicory can be
calculated. The microscopical appearances of the two powders differ,
coffee showing hexagonal cells and no laticiferous vessels, unlike
chicory. There is no law against selling mixed coffee and chicory, if
the fact that it is a mixture is stated; and the proportion of the
two unfortunately is not required to be stated. As a pound of coffee
costs five times as much as a pound of chicory, it is obviously to
the purchaser’s advantage to make his own mixture in the proportions

=The Preparation of Coffee= ought to be effected as in the case of
tea—by making an infusion and not a decoction, _i.e._ by pouring
boiling water on the coffee and allowing it to stand, but not
continuing the boiling. Continuance of boiling dissipates the delicate

Inasmuch as coffee contains a much smaller percentage of theine than
tea, more of the former must be used to obtain a beverage equally
refreshing with tea. Two ounces to a pint of boiling water are
required. The infusion thus made should be mixed with an equal part of
boiled milk. The coffee ought, if possible, to be freshly roasted.

The colour of coffee is no guide to its strength. Many of the black
coffees, especially “French coffee,” owe their colour to the caramel
(burnt sugar) contained in the chicory mixed with them.

Coffee has similar properties to tea, with some minor differences. (1)
Like tea, it is restorative and sustaining in its action, but seems to
act more quickly than tea. (2) Unlike tea, it does not tend to produce
perspiration, but rather a dry hot skin. (3) With some it is decidedly
laxative; while tea, especially if badly made, has an opposite effect;
but this is not always true. (4) It seems to have a greater power
of antagonising the effects of alcohol than tea; and is a valuable
antidote, after the action of an emetic, in poisoning by opium or
arsenic or alcohol.

As a rule, coffee is not so prone to disorder the digestion as tea,
but this is not universally true, and in some persons it always
produces “biliousness.” When taken in excess, it produces—besides
indigestion—palpitation, restlessness, irritability, sleeplessness, and
a condition of general nervous prostration; in fact, similar symptoms
to those produced by a prolonged over-indulgence in tea.

While the consumption of tea is rapidly on the increase, that of coffee
is steadily diminishing. This is partly owing to the greater expense of
coffee—a larger quantity being required to form a good beverage; and
partly to the greater difficulty in preparing good coffee.


Cocoa, or more properly cacao, is obtained from the seeds of the
_Theobroma Cacao_—a native of the West Indies, Mexico, and the central
parts of America. Its name Theobroma was given it by Linnæus, and means
the “food of gods.” The fruit is a large leathery capsule, having
nearly the form of a cucumber. It contains from 25 to 30 seeds, each
about the size of an almond. Before using, these are roasted like
coffee berries, and a peculiar aroma is developed in this process as in
the case of coffee. The beans or seeds are then manufactured into three
different products. (1) They are simply deprived of their husks and
broken to pieces; this forms =Cocoa-Nibs=. (2) They are ground, husk
and all, between hot rollers into a paste, and mixed with starch and
sugar; this forms =Cocoa=. (3) They are shelled and then ground into a
paste, as in making cocoa; sugar and some seasoning, usually vanilla,
being subsequently thoroughly mixed; this paste is =Chocolate=.

The purest form is the cocoa-nibs. When these are boiled in water, a
brownish decoction is formed, with the fat as a scum at the top; this
may be removed, and the decoction flavoured with milk and sugar. In
this form, cocoa can be taken by invalids with weak digestion, who
would be nauseated by the fat of ordinary cocoa or chocolate.

The best cocoa is prepared as above; but the lowest quality contains
the husks of the beans, with hardly any of the beans in it; a somewhat
better, though still inferior sort, is made from the smaller fragments
of the nibs, and a good deal of husk. In some cases the cacao butter
is removed during the process of preparation, and starch or sugar
substituted. This form is less likely to disagree with dyspeptics than
whole cocoa.

The action of the =Volatile Oil= (not the cacao-butter) developed
during roasting, is probably similar to that of tea and coffee, though
it is less =in amount=. The bitterness is greater than that of coffee,
but the astringency less than in either tea or coffee.

The =Concrete Oil=, or fat of cocoa, forms about half its weight. It is
white, and not apt to turn rancid, and possesses an agreeable flavour.
Cocoa also contains a certain amount of starch and cellulose.

=Theobromine= is a white crystalline alkaloid, the exact analogue
of caffeine. The latter, in fact, is methyl-theobromine—that is,
theobromine _plus_ the theoretical group CH₂. Theobromine possesses
similar properties to caffeine. It amounts to 1.5 to 2 per cent. of
the whole bean. The ordinary preparations of cocoa differ considerably
in composition as may be seen from the following table of per
centage composition (Ewell). In each instance other nitrogenous and
non-nitrogenous constituents go to make up the total 100:

  │                           │ FAT. │FIBRE.│CANE- │ ASH. │  ADDED   │
  │                           │      │      │SUGAR.│      │  STARCH. │
  │                           ├──────┼──────┼──────┼──────┼──────────┤
  │_Fry’s Cocoa Extract_      │ 30·9 │  3·9 │  ──  │  4·2 │  None.   │
  │_Schweitzer’s Cocoatina_   │ 31·1 │  3·7 │  ──  │  6·3 │   Do.    │
  │_Rowntree’s Cocoa Extract_ │ 27·6 │  4·4 │  ──  │  8·5 │   Do.    │
  │_Van Houten’s Cocoa_       │ 29·8 │  4·4 │  ──  │  8·6 │   Do.    │
  │_Epps’s Prepared Cocoa_    │ 25·9 │  1·5 │  26  │  3·1 │  Much    │
  │                           │      │      │      │      │arrowroot.│

Some of the preparations of cocoa (_e.g._ Van Houten’s) have added to
them alkaline salts to increase their solubility. Cocoa is not such
a valuable food as might appear from the large amount of fat in it,
because only moderate quantities of this can be taken without deranging
digestion. In Vi-Cocoa a certain amount of kola is added, which
contains a considerable proportion of caffeine. The addition of such a
drug to a beverage is distinctly to be deprecated.

=Minor Stimulants.=—Beverages containing theine, or some analogous
principle, appear to be employed in most countries. In moderate doses,
they may assist the assimilation of other foods, but their main
influence is on the nervous system. Theine-containing substances may
be described as both sedative and exciting. They are sedative, in that
they allay nervous irritability, and tend to “take the edge off” the
disturbance caused by outward circumstances; and they are exciting,
inasmuch as they are known to form an admirable antidote to the
stupefying effects of opium or alcohol. The wakefulness from tea is an
instance of the same thing, while the allaying of sensations of cold
and hunger by a cup of tea is an instance of the sedative effect.

 In Brazil, =Guarana= (from _Paullinia sorbilis_) is used as a drink;
 it contains theine, the quantity of which is twice as much as in good
 black tea, and five times as much as in coffee. Like green tea, a
 cup of guarana infusion is sometimes extremely valuable in nervous

 In Peru, the natives use the leaves of the =Coca= plant (_Erythroxylon
 coca_), which must be carefully distinguished from cocoa. It is
 chewed somewhat in the same way as the betel-nut. It contains two
 alkaloids—cocaine and hygrine, as well as tannin. In its stimulant
 action it resembles tea and coffee. The active principle of this
 plant, =Cocaine=, is a valuable local anæsthetic. Internally it has
 been taken as a stimulant and restorative. Various wines containing
 Coca, with vaunted restorative powers, are advertised. They are
 mischievous when taken frequently. Nature’s remedy for fatigue,
 whether mental or body, is rest and recreation. Stimulants of this
 class, even though they enable work to be continued for awhile,
 eventually increase the exhaustion for which they are taken.

 The =Kola-nut= is used in some parts of Western Africa as a stimulant.
 It is about the size of a pigeon’s egg, and has a bitter taste. The
 natives of Guinea generally take a piece of the seeds before each
 meal, and sometimes nibble it throughout the day.

 =Kava= is prepared from the root of a kind of pepper. The natives of
 the Fiji islands commonly indulge in it. Its effects resemble those
 of coffee. In large doses, it destroys the power of walking, and may
 possibly produce impairment of vision.

 The leaves of the _Ilex Paraguayense_, _Ilex Gongorrha_, and _Ilex
 Theezans_ are made into the beverage commonly known as =Paraguay tea=
 or maté.

 The leaves of the =Hydrangea Thunbergii= are made into a beverage,
 which is designated in Japan “the tea of heaven.”

 Among certain nations of Asia, the =Betel-nut= (from a palm called
 _Areca Catechu_) is chewed, after mixing small fragments with pepper
 and quicklime, and rolling in a palm leaf. The saliva is tinged
 blood-red, and a narcotic effect is said to be produced.

 The dried flowering tops of the =Indian Hemp= (_Cannabis Indica_)
 are smoked by the Malays and others, or made into a beverage, called
 haschisch, which produces a kind of intoxication, in which murder has
 often been committed (hence, _assassins_ equals haschascheens).

 The Kamtschatkans drink an infusion made from a fungus, known as the
 =Fly Agaric= (_Amanita Muscaria_), thus producing an intoxication
 similar to that from haschisch.

 =Opium= in small doses is a stimulant, in large doses narcotic.
 The crude drug is sometimes taken, and less frequently the
 active principle, Morphia. It is frequently smoked, as well as
 taken internally. It is to be feared that secret opium taking
 is considerably increasing. The taking of morphia, especially
 hypodermically, is too common. Generally it has been first prescribed
 for neuralgia or some other complaint causing acute pain; and the
 patient, having experienced relief by its means, is tempted to revert
 to the practice apart from medical advice. Such a line of action is
 most pernicious. Eventually both the physical and the moral nature of
 the victim are shattered by it; and to break off this insidious habit,
 when once thoroughly established, is most difficult.

 =Tobacco= may be conveniently mentioned here, though its usual effects
 are certainly not stimulant. It is smoked, chewed, or taken as snuff;
 when indulged in to excess it produces serious depression of the
 heart’s action, with frequent intermittence. In moderate doses it is
 sedative as well as slightly laxative. Prolonged indulgence in tobacco
 has produced many cases of incomplete blindness (_tobacco amblyopia_),
 in some cases it comes on with much smaller doses, and in all cases is
 only curable by ceasing to smoke. There is no sufficient ground for
 the statement that cigarette smoking is more injurious than smoking
 tobacco in a pipe or cigar, unless in the former case the smoke is
 inhaled into the lungs. The practice of smoking is injurious to
 growing boys, and should be strictly forbidden.

 =Other Drugs= are now not infrequently taken, apart from medical
 advice. Of these the most commonly used are =Antipyrin= and
 =Phenacetin=, for headaches. Their use is injurious, and should not
 be entertained as a frequent practice. Sleeplessness frequently leads
 to the practice of taking chloral or sulphonal, or occasionally
 the inhalation of chloroform to induce sleep. (See also page 259).
 Remedies to induce sleep should never be taken except under immediate
 medical advice. They are only justifiable in extreme conditions, and
 if frequently taken tend to aggravate the conditions for which they
 are given.



=Properties of Alcohol.=—When a saccharine solution is subjected to the
influence of warmth and moisture, and exposed to the air, it rapidly
undergoes a process of =fermentation=. The most favourable temperature
is about 70° Fahr. The ferment or agent exciting the change in the
sugar is derived from the atmosphere; it is a minute fungus (_torula
cerevisiæ_), the spores of which are constantly floating in the air.
When once fermentation has started, exposure in the air is no longer
necessary; the process continues in closed vessels. The essential
change occurring in the vinous fermentation is that grape sugar
(C₆H₁₂O₆,H₂O) becomes split up into alcohol (C₂H₅OH) and carbonic
acid (CO₂). Thus—

                     C₂H₆O }
                     C₂H₆O }  Two of alcohol
  C₆C₆H₁₂O₆  =
                     CO₂ }
                     CO₂ }     Two of carbonic acid.

There are other fermentations allied to the vinous. Thus the =Acetous=
fermentation results in the conversion of alcohol into vinegar, as in
the souring of beer or wine. The =Lactic= fermentation leads to the
conversion of milk-sugar into lactic acid, with consequent souring of
the milk.

=Alcohol=, or more correctly ethylic alcohol, is a colourless liquid,
having a pleasant vinous odour, and evaporating rapidly on exposure to
air. It burns with a bluish sootless flame, and is a capital solvent
for resins and other substances.

_Rectified spirit_ is absolute alcohol mixed with 16 per cent. of
water. _Proof-spirit_ is a mixture of 42·7 per cent. by volume of
absolute alcohol, and 57·3 per cent. of water. Thus the ratio of
alcohol to proof-spirit being as 1: 1·76, the amount of alcohol in
any liquid being given, the amount of proof-spirit can readily be
calculated. The fermented drinks containing alcohol may be classed as
(1) malt liquors, (2) wines, and (3) distilled spirits. The relative
properties of these will be considered afterwards; in the next two
sections will be considered the effects of diluted alcohol in whatever
form it is taken.

=Effects of Moderate Doses of Alcohol on the System.=—In studying the
physiological effects of alcohol, one has to guard against the fallacy
that these are the same, only differing in degree, whatever the dose
may be. The effects of large doses of alcohol are almost exactly the
reverse of those produced by small doses. It will be necessary to
define, therefore, what we mean by a moderate dose. By a moderate
dose, we understand the amount of alcohol which can be taken without
any alcohol being eliminated in the urine. Dr. Anstie found that 1½
ounces, that is three tablespoonsful, of absolute alcohol, taken in
twenty-four hours, caused its appearance in the urine; and Dr. Parkes
and Count Wollowicz obtained almost precisely the same result. Anything
below some quantity between 1 and 1½ fluid ounces per day can be
disposed of in the system, and is probably oxidised like ordinary foods.

The amount of alcohol, in the form of alcoholic beverages,
corresponding to this =maximum dose= of absolute alcohol is
approximately as follows:—

  One imperial pint (20 fluid ounces)
     of bottled beer                              (5 per cent. of alcohol).

  One tumblerful    (10   „     „   ){of claret, hock, and}
                                     {other weaker wines  } (10  „    „  ).

  2½ glasses     (5    „     „   ){of port, sherry, and}
                                     {other strong wines  } (20  „    „  ).

  One glass         (2    „     „   )of brandy or whiskey   (50  „    „  ).

It will be understood, therefore, that in describing the effects of a
moderate amount of alcohol on the system, an amount below 1½ ounces
of absolute alcohol per day is meant, freely diluted, and taken as a
rule with meals.

1. =Effect on the Stomach.=—In very small quantities, alcohol seems
to stimulate digestion in the same way as mustard. But like all other
artificial helps to digestion, it is best avoided in the healthy

2. The =Effect on the Liver= is similar to that on the stomach—a
temporary redness and congestion being produced; this effect soon
disappearing if the dose is small and well diluted. But in all cases
where there is a tendency to biliousness, even small doses of alcohol
are injurious.

3. The =Effect on the Heart and Blood-Vessels= is first to increase
the force of the heart’s action and the rapidity of the pulse. The
stimulation of the heart is rapidly followed by a universal dilatation
of the small arteries of the body, which diminishes the blood-pressure.
Parkes and Wollowicz found that the daily administration of from 1 to
7½ ounces of rectified spirit raised the pulse rate by ten beats
per minute, as compared with other periods; and that this effect was
followed by a period of depression in which the beat was both slower
and feebler than usual.

4. The =Effect on the Nervous System= varies. In persons unaccustomed
to its effects, even small doses dull the power of thought and the
rapidity of perception, owing to the paralyzing effect which it exerts
on nerve cells. In most cases, however, it at first produces increased
rapidity of thought and excites the imagination, though even here
it makes it more difficult to keep to one train of thought. This is
clearly owing to the more rapid circulation of blood through the brain.
Dr. E. Smith’s experiments show that it diminishes the acuteness of
the senses. Its influence even in dietetic doses, on the capacity for
mental work, is slightly to diminish it.

5. The =Effect on the Muscular System= is never beneficial. Even when
only small quantities are taken, the power of controlling delicate
movements is slightly diminished. For persons engaged in laborious
occupations, a small quantity does not produce much apparent effect,
but where the quantity exceeds two fluid ounces per day the capacity
for strong and sustained muscular work is manifestly lessened (Parkes).
This effect is probably due partly to the dulling of the nervous
system, rendering the muscles less amenable to the will, and partly to
the over-excitation of the heart causing palpitation and breathlessness.

6. The =Effect on Metabolism= is to diminish it, thus favouring the
deposit of fat in the tissues. It acts as a poison to the protoplasm
of the cells of the body, diminishing their power to break down the
floating nutriment, especially fat and carbohydrate.

The =Effect on the Temperature= is to lower it; but unless the dose
is excessive, this effect is hardly appreciable. The resistance to
excessive cold is diminished by even moderate doses of alcohol, still
more by large doses. In the Arctic regions, this has been abundantly
proved. This effect is produced, notwithstanding the fact that alcohol
becomes oxidised in the system. The dilatation of the surface blood
vessels leads to a greater loss of heat than that produced by the
oxidation of the alcohol.

the definition given of a moderate dose, one is bound to admit that
a large number of individuals exceed this amount daily, apparently
without any very serious results. The system becomes habituated to
large doses, and if the occupation is a laborious one, they may in part
be oxidised in the system. Such, however, are exceptional cases. In
the majority of cases evil results are by no means confined to those
who indulge in very large quantities of alcohol at varying intervals.
In fact these very often escape comparatively free, while others who
never take a quantity sufficient to incapacitate them for their work,
are sowing the seeds of chronic and oft incurable disease. The labourer
who has a drinking bout at intervals is thoroughly nauseated; and the
condition of liver and stomach induced, enforces abstinence on him
for a time sufficient to bring his organs back to a normal condition;
while the city merchant who indulges more moderately, but whose organs
are almost continuously impregnated with alcohol, becomes gouty and
prematurely old.

The =Stomach= may become acutely inflamed, when a large dose of alcohol
is taken. The chronic irritation of alcohol, especially when taken
apart from meals, causes atrophy of the walls of the stomach, and a
change analogous to that in the liver.

The =Liver=, when alcohol is daily taken immoderately, becomes
seriously diseased. In some cases it becomes large and fatty; in others
the chronic irritation excites an overgrowth of fibrous tissue between
the lobules of the liver, which, gradually shrinking, squeezes the
liver cells and causes them to atrophy, at the same time obstructing
the small branches of the portal vein in the substance of the liver.
The consequence of this obstruction to the flow of blood through the
liver is that all the organs from which the portal vein brings blood
become overloaded with blood, and vomiting of blood and dropsy of the
abdomen occur at a later period.

The =Lungs= are irritated to a less extent by alcohol in large doses.
The tendency to chronic bronchitis is increased, followed by emphysema,
and sometimes an overgrowth of fibrous tissue (cirrhosis) like that in
the liver occurs.

The =Heart and Blood-vessels= tend to become diseased, owing largely to
the gouty condition of system developed.

The =powers of Metabolism= are diminished. Corpulence is, consequently,
a common result of alcoholism. There may also be fatty deposit in
the internal organs, such as the heart. This must not, however, be
confounded with a much more serious condition, fatty _degeneration_
of the heart, in which the substance of the muscular fibres becomes
partially converted into fat, and which also is sometimes due to

The =Nervous System= is more prone to suffer in chronic alcoholism
than any other part of the body, except perhaps the liver. The first
effect of a large dose of alcohol is to stimulate the nervous system,
as already described. This is followed by a dulling of the nervous
faculties, which comes on rapidly in proportion to the amount taken.
The phenomena of _intoxication_ are unhappily too familiar to require
description, mental incoherence and muscular incoordination (lack of
control over the muscles) being the most prominent features.

When the dose of alcohol is still larger, a condition of profound
unconsciousness is produced (_coma_), which may be difficult to
distinguish from other forms of unconsciousness.

=Delirium Tremens= is another nervous condition, which may rarely
follow a single debauch, but much more commonly affects the chronic
toper. In some cases the immediate exciting cause is a mental shock, or
lack of food, or a surgical injury. Alcoholic subjects suffering from
any acute disease are liable to this form of delirium, and their chance
of recovery is greatly diminished.

=Insanity= of a more prolonged character than that characterising
delirium tremens is an occasional result of alcoholism.

Besides the nervous diseases already named, a chronic thickening of the
membranes covering the brain and spinal cord, gradually progressing
and finally fatal, is often the consequence of prolonged alcoholic

=Various Degenerative Diseases= are produced by alcohol. It has been
well called by Dickinson the very “genius of degeneration.” Such
degenerations are by no means confined to the intemperate; they are
seen in those who are of what would usually be considered moderate
habits. The stomach, liver, lungs, and probably the kidneys, are the
main organs to suffer in this way. It is probable that the effect on
the kidneys only occurs when a gouty condition is developed. In all
these cases there is an overgrowth of fibrous tissue, with atrophy of
the proper gland structures.

=Gout= is the common nemesis of those indulging in alcoholic beverages,
more especially wine and beer, due to the excessive formation or
retention of urate of soda in the body. This produces inflammation of
the joints, and other evils—among them the gouty kidney, named above,
which is always ultimately fatal. Rigid arteries are likewise commonly
due to alcoholism and gout. If one of these bursts in the brain,
apoplexy results.

=Longevity= is diminished by immoderate indulgence in alcohol. The
statistics of Temperance Insurance Societies, show much better results
among teetotalers than among moderate drinkers. It is only fair to
add that although the latter are supposed to consist of moderate
drinkers—and particular enquiries are always made on this point before
insurance—it is probable that a large proportion of them exceed 1½
ounces of alcohol per day. Making due allowance for this fact, the
statistics show a great superiority in the expectation of life of

=Factors Modifying the Effects of Alcohol.=—1. =Age and Sex.=—Until
adult life is reached, total abstinence from alcohol should be
enforced. The delicate nervous system of children is easily disturbed
by it, and it appears in some measure to retard growth. Another
argument against giving alcohol before adult age is reached, is still
more important. It is at this period of life that habits are chiefly
formed, and a craving for alcohol may be insidiously produced, destined
to have most baneful results.

Old people, if ordered spirits for medical reasons, should drink them
well diluted.

Women are much more easily affected by alcohol than men, and if they
acquire the habit of excess, the hope of reformation is even less than
with men.

2. =Exercise= has a most important influence in modifying the effects
of alcohol. Those of sedentary occupations and living in towns, cannot
oxidise as much as those engaged in active out-door work, and are
consequently much more prone to suffer. A game-keeper in the Scotch
Highlands may possibly live to a good old age, notwithstanding the fact
that he consumes an amount of whiskey that would have sent a sedentary
man to his grave in the course of a few years.

3. =The Condition of the Stomach= has also great influence. When
the stomach is empty, alcohol produces at once a powerful reflex
stimulation of the heart, and becomes quickly absorbed into the
circulation. Thus intoxication may be produced by a quantity that would
have had little effect if taken with a meal.

4. =The State of Concentration or Dilution= modifies greatly the action
of alcohol, the local action on the stomach and the reflex stimulation
being much greater than when it is concentrated, and injurious effects
being much more likely to occur.

5. =Cold and Heat= modify the action of alcohol. A smaller quantity
of hot spirits and water will intoxicate than of cold; the heat
stimulating the heart, and so making the absorption of the alcohol more
rapid. A glass of hot spirits and water will often cause sleep, by
drawing the blood towards the abdominal organs. The fact that persons,
who have been drinking spirits in a warm room, on going out into the
cold air become suddenly intoxicated, seems opposed to what has been
already said. But probably this is due to the cold causing contraction
of the arteries of the skin, and so driving more of the blood loaded
with alcohol to the internal organs and the brain (Brunton).

6. =Mental Occupation= has some influence in modifying the effects of
alcohol. Topers have found that if they try to converse during their
debauch—the conversation implying increased functional activity of the
brain, and therefore a freer circulation of blood in it—intoxication
occurs much more readily, than when the mind is not active.

7. =Disease= modifies greatly the effects of alcohol. In some diseases,
as in inflammation of the lungs and in fevers, it can be given in large
quantities without producing intoxication; and in these conditions it
lowers the temperature. In other diseases, especially gout and kidney
disease, its use is nearly always followed by bad results.

=The Advisability of Alcohol as an Article of Diet in Health.=—In
dealing with this difficult point, two sets of facts require
consideration, those obtained as the result of =Physiological=
observations (see page 56), and those which are the result of
=Experience=. There can be no doubt that the former are much more
reliable than the latter. Experience is very prone to give fallacious
results, especially when questions of appetite are concerned. In
making a trial of abstinence, the mistake has been commonly made of
only prolonging the investigation for a few weeks, and then comparing
results. Such a method is, however, very unfair, and is certain to lead
to an unreliable conclusion.

The records of experience under certain conditions have, however, been
so extensive, as to lead to trustworthy results. It has been abundantly
proved that prolonged muscular work is best undergone during total
abstinence from alcohol; and that the extremes of heat and cold and the
exposure and exertions of marching armies, are best borne under similar

The artificial character of town life is commonly adduced as an
argument for the moderate use of alcohol. In the case of healthy
workers, this does not hold good; many of our hardest workers and
thinkers take no alcohol.

The universality of the habit of taking stimulants is a curious
argument on the same side, though if the habit be bad, this can be no
more reason for continuing it than can the prevalence of vice be an
excuse for indulgence in it.

The two chief physiological points bearing on the advisability of
alcohol as a part of one’s daily diet are—its =food properties=, and
its effect on the appetite and digestion.

It has been already stated that a quantity of alcohol under 1 or 1½
ounces may become oxidised in the system, and may thus form a source of
heat. But in all probability, although it may be regarded as a food,
it is a most inconvenient one, inasmuch as it diminishes the oxidation
of other foods. It has been aptly compared in this respect to
sulphur, which is an oxidisable material, but which, when it is burnt
in a chimney, in which the soot is on fire, will put an end to the
combustion of the latter. Its value as a food, under normal conditions,
is practically nil.

Its =Effect on the Digestive Organs= is three-fold. (_a_) The contact
of alcohol with the mucous membrane of the mouth and stomach, acts as a
reflex nervous stimulus, which in moderation excites an increased flow
of gastric juice. (_b_) It also increases the activity of the movements
of the stomach. In cases of weak digestion, therefore, small doses of
alcohol may, at times, be useful. (_c_) The effect of alcohol on the
food taken varies with its degree of dilution. Concentrated alcohol
coagulates albumin, and so stops digestion; largely diluted alcohol has
no such effect.

The late Dr. Parkes, the greatest authority on the dietetic use of
alcohol, has summarised the argument as to the dietetic use of alcohol
as follows:—

“But what, now, should be the conclusion as to the use of alcohol
in health after growth is completed? Admitting the impossibility
of proving a small quantity to be hurtful, and at the same time
acknowledging the dangers of excess, there arises an argument which
seems to me somewhat in favour of total abstinence. No man can say when
he has passed the boundary which divides safety from harm; he may call
himself temperate, and yet may be daily taking a little more than his
system can bear, and be gradually causing some tissue to undergo slow
degeneration. He may be safe, but he may be on the verge of danger.

“This uncertainty, coupled with the difficulty at present of saying
what dietetic advantage is gained by using alcohol, seems to me rather
to turn the scale in favour of total abstinence instead of moderate
drinking. But if any one honestly tries, and finds he is better in
health for a little alcohol, let him take it, but he should keep within
the boundary line, viz., that 1½ ounces of pure or absolute alcohol
in twenty-four hours form the limit of moderation. I do not then think
he can do himself any harm.”

=The Varieties of Fermented Drinks.=—The three chief kinds of alcoholic
beverages are malt liquors, wines, and ardent spirits. In addition, we
may mention cider and perry, which are the fermented juices of apples
and pears respectively; and koumiss, which the Tartars prepare by
fermenting mare’s milk, though it may also be made from the milk of
other animals.

All =Beers=, =Ales=, and =Porters= are prepared from malt, which is
the germinating grain of barley. The fermentation of the sugar in the
barley produces alcohol, the amount of which varies in different cases.
In Pilsener beer it is 3½ per cent. of absolute alcohol; in stout
and porter 5 to 6 per cent. The hop which is added to the fermenting
barley, gives to beer its characteristic bitterness.

=London Porter= is coloured with black or roasted malt; =stout= is only
a stronger form of porter. Bottled ales are generally stronger than
those on draught, and being slightly effervescent, may agree better.

The effect of alcohol in beer is modified by the _hops_, which help in
producing drowsiness. Beer has a marked tendency to produce obesity,
more so than any other alcoholic beverage. Its influence in the
production of gout is also very great.

=Substitutes for Malt= have been largely used. Thus by the action of
sulphuric acid on starch, an artificial form of sugar is produced,
which is largely used in place of malt for making beer. Many recent
cases of poisoning by arsenic have been traced to the use of impure
sulphuric acid in manufacturing this form of sugar.

 The detection of arsenic in organic liquids requires great care, as so
 many compounds of arsenic are volatile, especially in the presence of
 chlorides, as in beer. To _detect arsenic in beer_ a pint of the beer
 is evaporated to dryness, and treated with 20 c.c. of strong sulphuric
 acid, heated, and 20 c.c. of strong nitric acid added drop by drop.
 Violent action occurs: if possible 20 c.c. more of nitric acid are
 worked in. Transfer the liquid to a small flask, and expel the nitric
 acid by boiling. By this means all chlorine is expelled, the arsenic
 is oxidised and the organic matter destroyed. SH₂ gas is now passed
 into the acid liquid for some hours, the precipitated sulphur and any
 sulphide filtered off and extracted with ammonia, which dissolves any
 sulphide of arsenic. The liquid so obtained is subjected to Marsh’s
 test. (See page 216.)

In the making of beer from malt, the first stage is to malt the barley,
_i.e._ leave it spread on floors for ten days after soaking. This
allows germination to take place, in which process the insoluble starch
is converted into starch, dextrine, maltose and glucose. After the
dried malt has been screened to break off the sproutings, the brewer
places it in the mash-tub, with water, at a temperature of 160° F. This
completes the transformation of the starch into glucose. The =wort= is
now boiled to stop the process, and the albumin from the grain is thus
coagulated. Hops are added at this stage. The boiled liquid is passed
into shallow vessels and cooled. The proper temperature for “top” yeast
is 60° F., for “bottom,” or Bavarian yeast, a much lower temperature is
desirable. When the desired temperature is reached, the liquid is run
into the fermenting tun along with yeast. The varieties of beer are due
in part to the degree of completeness of fermentation of sugar allowed.
If too complete, the beer does not keep well.

=Wines= are produced by the fermentation of the juice of the grape.
The wine produced may be bottled before or after fermentation is
complete; in the former case, an effervescing wine is produced, such as
the sparkling wines of the Rhine and the Moselle, or champagne. When
the sugar is nearly all fermented a _dry_ wine is obtained, of which
Bordeaux and Burgundy, Hock and Moselle, are examples.

The difference in colour between red and white wines is produced by
allowing the juice in the former to ferment in contact with the skins,
from which the colouring matter is extracted by the alcohol. Both red
and white wines may be obtained from either red or white grapes. From
the skins also are extracted a salt of iron, and a peculiar form of
tannin. Tartaric and acetic acids, and tartrate of potass, are present
in varying quantities in wines; in old wines the tartrate separates as
bitartrate of potass, forming with tannin and colouring matter the
“crust” of port and other wines. The “bouquet” of wines is due chiefly
to certain volatile bodies, such as pelargonic ether. The proportion
of alcohol in wines varies from 6 to 14 per cent. As fermentation is
stopped by the presence of 14 per cent. of alcohol, any larger amount
of alcohol than this must have been added to the wine.

Wine, like beer, has a strong tendency to produce gout, especially
the sweet and strong wines. It has not, however, the same tendency to
induce obesity.

=Spirits= differ from the two last groups, to begin with, in the amount
of alcohol they contain. Thus, English beers contain from 3 to 6 per
cent., German beers from 2 to 5 per cent., wines from 8 to 20, and all
kinds of spirits from 37 to 58 per cent. of alcohol. They differ in
the absence of the bitter principle of beer and much of the salts and
sugar and ether of wines. They are all prepared by the distillation
of some previously fermented liquor. =Brandy= ought to be made by the
distillation of wine; and then contains, besides alcohol and water,
small quantities of acetic, œnanthic, butylic, and valerianic ethers.
But much of the brandy sold is simply made from potato spirit, by the
addition of acetic ether, burnt sugar, etc. The starch of potatoes
is converted into dextrin and dextrose by dilute acids, and then
fermentation allowed. By the use of patent stills, all bye-products
can be separated, a fairly pure alcohol known as _silent spirit_ being
produced. This is largely employed in manufacturing spirits and in
fortifying wines.

=Whiskey= is prepared from malted barley, or from a mixture of grains,
to which a sufficiency of malt to convert their starch into sugar has
been added. In _grain whiskey_ the distillation is effected by steam
in a patent (Coffey’s) still, which separates most of the bye-products
(fusel oil, etc.) from the spirit. In _malt whiskey_, distilled in the
old-fashioned pot-still, these bye-products are not separated.

The improvement of whiskey effected by keeping is not due (Bell) to
the diminution of fusel oil. Such a diminution does not occur. The
percentage of alcohol diminishes by keeping, 6 to 8 per cent. proof
spirit being lost by five years’ storage in wood. “Fusel oil” is a
mixture of alcohols of higher boiling point than ethylic alcohol
(amylic, propylic, etc.). Even in a bad whiskey not more than 1∕10
per cent. of fusel oil is present (about one grain in a glassful).
Experimentally no marked effects have been produced by fusel oil, when
it is less than 1 per cent. Possibly the presence of furfurol, of
which there is a trace in malt whiskey, which disappears on keeping,
may partially explain the disagreeable flavour of new whiskey. But it
is fairly clear that those who argue that it is _bad_ whiskey and not
_good_ whiskey which does harm are speaking without knowledge. It is
not the quality but the quantity of whiskey which is responsible for so
much moral and physical evil.

=Gin= and =Hollands= are obtained from barley, and flavoured with
juniper berries and other materials. The oil of juniper stimulates the
urinary excretion.

=Rum= is obtained by the distillation of molasses, and is usually
kept for a long time in oak barrels. It is said thus to acquire more
astringent matters than other spirits contain.

The =legal limits= of dilution of whiskey, brandy and rum is down to 25
degrees under proof, and of gin down to 35 degrees under proof. (For
definition of proof spirit, see page 55). The amount of alcohol in an
alcoholic liquor is determined by distillation of 100 c.c., making up
the distillate to 100 c.c. by the addition of distilled water, and then
taking the specific gravity of a portion of this liquid by the aid of
the specific gravity bottle. The percentage of alcohol corresponding to
a given specific gravity is given in tables prepared for this purpose.

Prolonged indulgence in spirits produces the various organic diseases
already described, and unless well diluted they are more harmful than
beers or wines. They differ from wines and beers in not tending to
produce gout, and from beer in not leading to obesity.



=Uses of Water.=—Water is a prime necessity of life. In its absence
life can only exist in lowly organised beings, and in them only in
a dormant state. From a hygienic point of view, the uses of water
are four-fold:—(1) It is =an essential part of our food=, not only
serving to build up the tissues of the body, but also preserving the
fluidity of the blood and aiding excretion of effete matters. (2)
It is necessary for =personal cleanliness=, of which the importance
can scarcely be exaggerated. (3) =In the household= it is essential
for cooking, as well as for washing the house, the linen, and
various utensils. (4) By =the community at large= it is required
for water-closets and sewers, for public baths, for cleansing the
streets, and for horses and other domestic animals, as well as in
many manufacturing processes. It is obvious that the water to be used
for domestic and general purposes, need not be so pure as that for
drinking purposes. Hence, a double supply was proposed for London in
1878, by the Metropolitan Board of Works—a less pure river supply for
general purposes, and a deep chalk-well supply for drinking purposes.
The scheme, however, rightly fell through, because of the expense of a
double source of supply, and the danger that the impure water would,
through carelessness or ignorance, be often used for drinking purposes,
when it happened to be nearest at hand.

=Quantity of Water Required.=—The quantity of water required for all
purposes has been variously stated by different authorities. The
quantity required for drinking purposes is found to bear a relation
to the weight of the individual, being nearly half an ounce for every
pound weight, or 1½ gills for every stone weight. Thus, a man
weighing 150 lbs. would require 3-3∕4 pints. Of this water, about
one-third is taken in the food; the remainder, averaging 2½ pints,
being required as drink. If we add the water required for other
purposes, according to De Chaumont, 1 gallon is required for drinking
and cooking, 2 gallons (not including a bath) for personal cleanliness,
3 gallons for a share of utensil and house washing, 3 gallons for
clothes washing; and if a general bath be taken, 3 gallons more; making
a total of about 12 gallons, to which 5 gallons must be added if there
is a water closet.

In hot summer weather the consumption is about 20 per cent. above the
average of the year; and frost often increases the amount 30—40 per
cent. above the average, owing to the bursting of pipes, or the loss
from taps foolishly left open to prevent bursting.

Water companies usually reckon 30-60 gallons for each individual, to
allow for the water required for scavenging and manufactories and for
waste. In large houses and hotels where baths are freely used, often
as much as 70 gallons per head is used, and in hospitals the amount
averages from 60 to 90 gallons per head. The following is Parkes’
estimate of the daily allowance for all purposes:—

  │                         │GALLONS PER HEAD│
  │                         │ OF POPULATION. │
  │                         ├────────────────┤
  │_Domestic supply_        │       12       │
  │_General baths_          │        4       │
  │_Water-closets_          │        6       │
  │_Unavoidable waste_      │        3       │
  │                         │       ──       │
  │    _Total house supply_ │       25       │
  │    _Municipal purposes_ │        5       │
  │    _Trade purposes_     │        5       │
  │                         │       ──       │
  │        _Total_          │       35       │

It has been proposed to put a water-meter to each house, so that the
rate may be in proportion to the amount of water used. The plan is
objectionable for two reasons: 1st—Because it tends to restrict the
necessary use of water for purposes of cleanliness. A scant supply of
water is always followed by uncleanliness of house and person, with
its consequent diseases; at the same time closets may be imperfectly
flushed, and may become choked. 2nd—Because of the primary expense of
the meter, and of its maintenance.

SOURCES OF WATER SUPPLY.—All our drinking water is obtained in the
first instance, by a natural process of distillation on a large scale.
The sun is constantly causing evaporation from sea and land. The vapour
produced, being condensed by a lower temperature, returns to the earth
as snow, dew or rain. All these natural products have been at times
utilised as sources of drinking water.

1. =Dew= has on rare occasions been utilised at sea by hanging out
fleeces of wool at night and wringing them out in the morning. A much
better plan is—

2. The =Distillation of Sea-water=. This can easily be managed now that
steam power is so largely used. It has even been employed on land, when
it was necessary temporarily to continue the use of water derived from
an impure source. The first part distilled should always be rejected,
as it is always impure. Distilled water is “flat” in taste, owing
to its containing no dissolved gases. It can be aërated by letting
it drop a considerable distance from one cask into another, through
small openings in the upper one, and by filtration through charcoal.
Non-aërated water is not easily absorbed into the circulation, and
occasionally causes illness.

3. The utility of =Melted Snow and Ice is= obviously very limited.
Moreover, its use is not free from danger if the ice is derived from
contaminated water. Outbreaks of enteric fever have been traced in the
United States to the taking of ice obtained from impure water.

4. =Rain-water= is a much more important source of water supply, and
after passing through the soil it constitutes the chief part of the
water we drink. The term, however, is properly restricted to the water
collected immediately after its descent from roofs, etc. Its purity
depends on three conditions—the character of the air it passes through,
the cleanliness of and absence of lead from the channels through which
it runs, and the condition of the water-butts in which it is stored.
Rain-water is soft; in fact, too soft to be pleasant to the palate. In
passing through the air, it carries with it a certain proportion of its
constituents; in towns especially ammonia, soot, etc.; near the sea,
it generally contains some salt; and being soft and having dissolved
oxygen from the air, it dissolves an appreciable amount of lead from
roofs or gutters.

The Rivers Pollution Commissioners found that out of eight samples
of stored rain-water only one was fit to drink. They came to the
conclusion that rain-water, collected from the roofs of houses and
stored in underground tanks, is “often polluted to a dangerous extent
by excrementitious matters, and is rarely of sufficiently good quality
to be used for domestic purposes with safety.” Also, that in Great
Britain, and more particularly in England, we shall “look in vain to
the atmosphere for a supply of water pure enough for dietetic purposes.”

The use of rain-water for drinking purposes is only justified in
isolated country houses where no better source is available; and under
these circumstances the greatest care should be taken to prevent
contamination with lead or organic impurities.

The amount of water falling on any impervious material obtainable from
rain can easily be estimated, if the amount of rainfall and the area of
the receiving surface are known. The average annual rainfall in this
country is 33 inches (see page 236).

 We may assume the amount practically available to be 20 inches per
 annum, and the area of the receiving surface 500 square feet. Multiply
 the area by 144, to bring it into square inches, and this by the
 rainfall, and the product gives the number of cubic inches of rain
 which fall on the receiving area in a year. One cubic foot, or 1,728
 cubic inches, of water being equivalent to 6·23 gallons, the number of
 gallons of water can be easily calculated. To calculate the receiving
 surface of the roof of a house, do not take into account the slope of
 the roof, but merely ascertain the area of the flat space actually
 covered by the roof. This may be done roughly by calculating the area
 of all the rooms on the ground floor, and allowing an additional
 amount for the space occupied by the walls. It has been estimated
 that, even if a rain-water supply for towns were desirable, the amount
 collected from the roofs of houses would scarcely average two gallons
 per person daily—assuming the average rainfall to be 20 inches, and
 that there was a roof area of 60 square feet for each individual.

The amount practically available from rain falling on different soils
varies with their porosity and slope. Thus, according to Professor
Rankine, the proportion of the total rainfall available is as follows:—

 Nearly the whole on steep surfaces of granite, gneiss, and slate;

 From three to four-fifths on moorland hilly pastures;

 From two-fifths to half on flat cultivated country; and

 None on chalk.

By available rainfall is meant the amount remaining after allowing for
percolation, etc., which can be stored in reservoirs.

5. =Upland Surface Water= is the water collected in hilly districts, as
on moorlands, at the head of a river. By its utilisation for drinking
purposes, the sources of water for the river are interfered with, and
any water company or local authority using such a source is, therefore,
required to run into the stream a quantity of water equal to a third of
the available rainfall. The limited and regular supply thus furnished
to the stream is found to be advantageous for industrial purposes as
its flow is equalised, and the violence of floods mitigated.

In the utilization of upland surface water the water from the
surrounding hills is collected at the bottom of a valley, in an
artificial, strongly-constructed lake; or in a natural lake, as in Loch
Katrine (from which Glasgow is now supplied).

Upland surface water is nearly always soft. Its use is much more
economical than that of hard water. It may be brownish, from the
presence of peat, but this is not objectionable, so far as health is
concerned. Its occasionally solvent action on lead is a more serious
objection. The population of many parts of Yorkshire and Lancashire
have suffered severely from chronic lead poisoning, due to the action
of certain upland surface water on lead service pipes. Only the waters
giving an acid reaction possess this plumbo-solvent power. (See also
page 82.)

6. =Springs= supply water which, originally derived from rain-water,
has percolated through the soil until it reaches some impervious
stratum, and has then run along this, until it arrives at the point at
which the impervious stratum reaches the surface of the soil. A spring
is thus the outcrop of the underground water. Springs are divided into
(1) land springs, and (2) main springs. The former flow from beds of
drift or gravel lying on an impervious stratum. They are very subject
to seasonal variation, and may dry up in certain years; while main
springs occurring in chalk, greensand, or other regular geological
formation, constantly supply a certain amount of water. Springs often
occur in connection with “faults” in geological strata, and then may
appear on table-lands and high elevations, unlike springs caused by
alternation of strata in valleys of denudation. The two kinds of
springs are shewn in Fig. 5 and 6.

In the land spring water crops out at the point where the porous
stratum ceases. Deep springs may crop out in the same way as land
springs, except that they appear at the bottom of deeper strata. Or
they may be formed by faults. Both these are shown in water having
percolated through the chalk beneath the superficial clay, is stopped
at the “fault” by the lack of continuity of the chalk stratum, and is
consequently confined under pressure. It therefore makes its way to the
surface, forming a spring. In its passage underground, water (owing
partly to the carbonic acid it has obtained from the air and soil), is
able to dissolve small quantities of chalk, sulphate of lime and of
magnesium, and traces of oxide of iron, aluminium oxide, and silica.
Spring-water possesses an equable temperature, generally about 50°
Fahr., while impounded or river water is always warm in summer and cold
in winter. Spring water is well-aerated, while river water, and still
more rain-water, are flat.

[Illustration: FIG. 5.—LAND SPRING.]

[Illustration: FIG. 6.


7. =Wells= may form the best or worst sources of water-supply according
to their depth and the means of protection against contamination. There
are two kinds—_Surface wells_ and _deep wells_.

=Surface Wells= do not usually descend further than 15 or 20 feet,
and have no impervious stratum between the source of water and the
surface of the well. They catch the subsoil or underground-water, which
percolates into them from the surrounding soil, and the character of
the water they receive will therefore vary with the nature of their
surroundings. If there is a cesspool near, this may simply drain into
the well. All the soakage from a considerable distance may find its way
into the well. In villages and isolated places the water of surface
wells is commonly contaminated. One hole may be dug in the garden for
a well, and another for a cesspool, while there is possibly a farmyard
near at hand—the soakage from the cesspool and farmyard soaking into
the well. Danger may also arise from more distant contamination. The
ground water which is tapped by the well is an underground stream
flowing towards the nearest brook. Heavy rains swelling the ground
water may wash impurities from cesspools, leaky drains, etc., at
a considerable distance, and carry these into wells lying between
these sources of pollution and the brook into the bed of which the
underground water ultimately discharges. The danger of contamination of
the water in the well by the contents of the cesspool is much greater
in the relative position shown in A than in the position shown at B,
Fig. 7. After heavy rain, when the underground water is swollen, the
danger of contamination is still further increased. The model bye-laws
of the Local Government Board state that a cesspool must be at least
40 feet distant from any well, spring, or stream. Probably this is
insufficient for safety; cesspools ought to be entirely forbidden. If
necessary to retain a surface well, it should be protected nearly to
the bottom with brick, lined with an impervious layer of cement so as
to prevent water from entering the well except near its bottom. In
modern wells iron cylinders are employed to line the upper part of the
well; and large glazed earthenware pipes arranged vertically and with
water-tight joints are sometimes used for the same purpose.

[Illustration: FIG. 7.

(_after Galton_).]

=Deep Wells= are made by digging a surface well, as above, except
that the ground water is prevented from entering the well by means of
impervious steining; and then boring from the bottom down through the
subjacent impervious stratum until a water-bearing stratum is reached.
The difference between a surface well and a deep well is shown in
Fig. 8 by A and B. Where the water in this stratum is retained under
pressure, deep wells are known as =Artesian Wells=. Such Artesian wells
have been sunk in London. Rain, falling on the chalk hills which lie to
the south and north of London, percolates through the chalk downwards,
and then laterally, until it lies in the concave London basin. Here the
clay stratum above it prevents its escape upwards; and being confined
under considerable pressure, it rises to the surface, or into a well
in the superficial gravel, when the clay is tapped. In Fig. 8, B is an
Artesian well if the pressure is such as to make the water rise through
the London clay, when this is cut through and the underlying chalk
is reached. C is a well in the chalk, which does not pass through an
impervious stratum, and therefore comes within the above definition of
a surface well; but as regards depth required to be dug before water is
reached it is more like a deep well.

[Illustration: FIG. 8.


Among the deepest Artesian wells are Grenelle (1,800 feet), and
Kissingen (1,878 feet.) The sinking of a deep well and severe pumping
of its water may exhaust all the neighbouring wells for two or three
miles. There is also danger of contamination from neighbouring
cesspools when the upper part of the deep well is not properly
constructed. The area exhausted by a deep well undergoing pumping is
represented by an inverted cone, having a very wide base, and with a
convex inner surface pointing towards the well.

For country places deep-well water is much preferable to water from
streams, as streams are very liable to be contaminated by the sewage
of houses higher up in their course, or even by that of houses close
by. A good well should be at least thirty feet deep—preferably fifty
feet and should always be lined with impervious material, except near
its bottom. The absolutely water-tight and impervious condition as well
as the distance of all drains or cesspools in the vicinity should be
ascertained before deciding whether the drinking water from a given
well is above suspicion. The direction of flow of the underground water
should also be determined. This may be done by measuring the level of
all the wells in the neighbourhood. Possible sources of pollution at
points from which ground water is flowing towards the well are much
more dangerous than those nearer than the well to the river towards
which the underground water is flowing (see Fig. 7). Steam pumping
greatly increases the area from which contamination may be derived.

An excellent plan to obtain water for villages, in a gravelly soil, is
to sink a Norton’s Abyssinian tube well for fifty or sixty feet.

In towns it is preferable to trust to the public water supplied, rather
than to any private well; and in villages, a general supply from a pure
source should also be provided.

The water is obtained from a well by a _pump_ or a _draw-well_. The
former is a safer as well as a less laborious plan. The pump should be
fixed some distance from the well, and the aperture through which the
pump pipe passes should be rendered water tight. Lead pipes should be
avoided, as well water not infrequently has plumbo-solvent properties.

8. =Rivers= and running streams originate in upland surface water
or springs, and their water should be of the same quality as these.
Unfortunately, they acquire a large amount of impurities in their
course. Towns commonly pour their more or less clarified sewage into
them; and the discharge of crude sewage from hamlets and single
houses on the banks is still far from uncommon. With the more rigid
enforcement of the Rivers Pollution Acts, this pollution of rivers
will become less frequent; but river water previously contaminated by
even small amounts of sewage cannot be regarded as an ideal source of

If no contamination be present in the water of a river, it forms a good
source of water-supply; being running water, it is always fairly well
aërated, and is not usually so hard as spring-water.

Even if sewage has entered a river, it is asserted that it becomes a
safe source of water-supply, after passage through filter beds, the
sewage having been got rid of in four ways.

1st.—By _subsidence_, the organic matter settling to the bottom.

2nd.—By the influence of _water-plants_, which assimilate ammonia,
nitrates, etc., and give out nascent oxygen.

3rd.—_Oxidation._ Doubtless a large amount of the nitrogenous matter
does become oxidised in its course down a river, and in this condition
is harmless. The river Seine becomes greatly polluted as it passes
through Paris, but so far as chemical analysis can determine its
condition, it is purer 30 miles below the city than it was before it
received the sewage of the city.

4th.—It is highly probable that the germs (or micro-organisms) of
enteric fever and other diseases known to be propagated by polluted
water, are practically or wholly destroyed in the struggle for
existence with the natural micro-organisms of river-water. When to
this is added the fact that river-water supplied to large communities
is carefully filtered through sand, after having been stored in
reservoirs, in which the chief impurities have time to settle, it is
not surprising that the experience of those communities like London,
which are supplied with river-water, usually shows no evidence of evil
ascribable to drinking this water. For over 30 years the inhabitants
of London have been drinking filtered water from the river Lea and
from the Thames above Teddington, and this gigantic experiment on a
population which has increased from 2½ to 5 millions has not been
accompanied by any conclusive evidence of evil effect.

In regard to the comparative merits of the various waters described,
it will be useful to give here the classification made by the Rivers
Pollution Commissioners in their sixth report:—

               { . Spring Water               }_Very palatable_.
  _Wholesome_  {2. Deep-well Water            }
               {3. Upland Surface Water         }
                                                }_Moderately palatable_.
               {4. Stored Rain Water            }
  _Suspicious_ {5. Surface Water from Cultivated     }
               {     Land                            }
               {6. River Water to which Sewage gains }
  _Dangerous_  {     access                          }
               { 7. Shallow-well Water               }

Passage through certain geological strata has a great influence in
rendering water palatable, colourless, and wholesome by percolation.

The following strata are said by the Commissioners to be the most
efficient:—(1) Chalk, (2) oolite, (3) greensand, (4) Hastings sand, (5)
new red and conglomerate sandstone. Fissures or cracks in these strata
may cause the water to pass through them unpurified by filtration.



The methods of storing and delivering water will vary with its source.
In rural districts, deep wells and springs are the best sources of
supply; but in large towns they are found to be insufficient for
the wants of a rapidly-increasing population; and they can only be
multiplied in a given district within certain limits, as every well
drains a large surrounding area. The supply from surface wells in
gravel or sand beds or in chalk districts is liable to fail in seasons
of drought; but deep wells in oolite or chalk formations, and in the
new red sandstone, generally yield a constant and abundant supply.

When the water is supplied from upland surfaces, springs, or small
streams, =a collecting reservoir= is required. This is generally
a natural valley below the level of the source of supply, but of
sufficient elevation above the place supplied to allow the water to be
distributed by gravity, without any pumping apparatus. The reservoir
should be large enough to hold five or six months’ supply, and its
embankment should be perfectly water-tight, and of great strength.

When water is collected from upland surfaces, it is important to know
the amount of rainfall to be reckoned on. If we know the area of the
surface which drains towards the reservoir, and the average rainfall,
the _total_ rainfall is easily calculated. This will, however, differ
greatly from the _available_ rainfall, owing to the losses from
penetration into the ground, evaporation, and other causes. The amount
lost will vary, according to the season, from one-half to seven-eighths
of the total rainfall; and according to the soil (page 68). The
proportion of percolation in the chief water-bearing strata surrounding
London varies from 48 to 60 per cent. (Prestwich). It is less when the
ground is steep and the rainfall rapid, and usually less in winter than
in summer.

Water collected near its actual place of fall, and from uncultivated
districts, is always purer than that collected further from its source,
and from cultivated land.

From the collecting or impounding reservoir, water is carried by the
aqueduct or conduit either directly into the service-pipes, or when the
pressure is too great, into a second =service-reservoir=, resembling
the impounding reservoir in general structure, and capable of holding a
few days’ supply.

This must be high ground, above the level of the highest houses to
which water has to be supplied, as water cannot rise above its own
level. When this cannot be arranged, the water is pumped into tanks at
a higher level, and distributed from them.

The greatest hourly demand for water being double the average hourly
demand, the water-mains supplying a town must have double the
discharging power that would be required, supposing the demand was
uniform. The first requisite of a supply of water is that it should
be abundant, and sufficient in amount for any extra strain on its
capacities. Water ought to be laid on to every house, and to at least
two floors of the house. Anything preventing free access to water,
militates against cleanliness.

=Cast-iron= is the most serviceable material used in the construction
of the main water-pipes; it is coated with pitch, or Dr. Angus Smith’s
varnish, or with magnetic oxide of iron (Barff). The service-pipes to
each house are generally made of lead, and the ease with which this
material can be bent and curved, and carried to the different floors
of a house, makes its use very convenient. Lead pipes, furthermore,
can be easily obliterated in case of bursting, and so any waste of
water and flooding of the house minimised. Some kinds of water,
unfortunately, act on and dissolve lead; this is especially true of
soft waters and those containing organic matter. Shallow wells, being
very liable to organic pollution, ought never to have the supply-pipe
of their pumps made of lead. With hard waters, lead pipes may generally
be used safely. When the quality of the water renders lead pipes
objectionable, the use of iron, tin, zinc, tinned copper, earthenware,
gutta-percha, and other materials, has been suggested. Of these, cast
and wrought-iron pipes are the most serviceable, or pipes composed of
an inner lining of block-tin and an outer of lead, a layer of asbestos
intervening to prevent galvanic action between the metals. According
to Rawlinson, “supply-pipes of wrought-iron are cheaper, stronger, and
more easily fitted than service-pipes of lead;” but it is urged against
them by Perry, that with soft water they become choked by rust in a few
years. If galvanized they are more durable. Cast-iron pipes are rusted
less easily than wrought-iron.

When the water-supply is from a river, filtering beds are needed, in
addition to the parts of a water-service hitherto described. Moreover,
since the river is usually at a low level, the water, after passing
through the filtering beds, requires to be pumped into raised tanks,
from which it is delivered.

In laying down water-pipes, in the streets and to houses, it is
very important to make the distance between them and all drains and
gas-pipes as great as possible. Suction of gases or liquids may occur
into leaky pipes, even though these contain water, and still more
when they are empty; and disease has occasionally been traced to this
source. Thus if sewers and water-mains are laid in the same trench,
foul matters which have escaped into the soil from the former may be
sucked into the latter. This may happen if the water-mains are leaky,
even when they are running full. Experiments have shewn that the flow
of water causes a partial vacuum and insuction at the defective points.
During intermissions of supply when the mains are partially or entirely
empty, the danger of leakage into them is still greater. Coal-gas has
been similarly sucked into water-mains.

The pipes bringing the water to a house may be kept constantly filled
with water, or only for a limited time once or twice a day. The
intermittent system of supply necessitates the provision of cisterns
or water-tanks, in which water can be stored in the intervals of flow
of water. With a sufficient and properly-distributed public supply of
water, no cistern ought to be required.

=Cisterns.=—Cisterns for the supply of potable water may be made of
iron, slate, stone, glass, glazed earthenware, or brick lined with
Portland cement. Other materials have been used, as timber, lead,
and zinc. _Timber_ is inadvisable, as it easily rots; _lead_ is very
objectionable, owing to the possible solvent action of the water on it.
_Zinc_ or galvanized iron cisterns are also acted on by soft water;
but they may be used with most waters. Galvanized iron is iron coated
with a thin layer of zinc. Iron cisterns soon rust; but this may be
prevented by giving them a coating of boiled linseed oil before they
leave the foundry. _Stone cisterns_ are too heavy for use, except in
basements. _Slate cisterns_ are good, but are apt to leak; the points
of leakage have occasionally been stopped with red lead, which is
attacked by the water, and thus lead poisoning results. If the slate is
set in good cement (not mortar, as this makes the water hard), it is a
good material for a cistern.

Every cistern should have a _well-fitting lid_, always kept closed, to
avoid the entrance of dust of various kinds, or even dead cats, birds,
etc. Noxious gases may be absorbed by the stagnant water.

The cistern should be _easy of access_. If it is indoors, the cistern
room should be well ventilated; and in any case the cistern should
be periodically visited and cleaned out. When the cistern is full, a
ball-tap prevents any further flow of water; and if this does not act
properly, an overflow pipe carries off the excess of water.

Cisterns badly arranged or neglected have been in the past a common
source of disease. (1) The _overflow pipe_ should not pass into any
part of the water-closet apparatus or the soil-pipe, or into the supply
pipe to the water-closet.

Where the overflow-pipe discharges into the soil-pipe or closet pan,
foul gases or even solid particles may find their way into the cistern.

(2) _No water-closet_ ought to be supplied from the same cistern as
supplies drinking water, as the pipe leading down to the closet may
when the cistern is accidentally empty carry noxious effluvia into the
cistern. A separate flushing cistern capable of discharging two to
three gallons of water should be provided for each closet.

With a constant supply of water, cisterns are only required for
water-closets and for hot-water apparatus (see pages 168 and 164).

=Constant and Intermittent Services.=—With an intermittent service
of water, during the intervals of supply, water is only obtainable
from cisterns, water-butts, etc. The objections against this system
are that—(1) The cisterns required are expensive, and liable to get
out of order and become foul. (2) Their overflow pipes may improperly
communicate with the soil pipe or with some other part of the drainage,
instead of opening into the external air. (3) Putrid gases, from
neighbouring ventilating-pipes or other parts of the drainage system,
are liable to be absorbed by the stagnant water in the cistern. (4) The
chief objection to an intermittent supply is that, during the intervals
in which the water-mains are empty, foul air and liquids from the
contiguous soil and drains are liable to be sucked through imperfect
joints into the pipes. (5) In case of fire, the supply of water in the
system is insufficient. In certain towns rates of insurance against
fire have been reduced on replacing an intermittent by a constant
service of water.

On the other hand it is urged that more expensive fittings are required
for a constant service; and that, when taps are left open or pipes
burst, the waste of water is much greater than with a cistern supply.
The balance is decidedly in favour of a constant supply without
storage cisterns. Where storage cisterns are in use, the taps for
drinking-water should be connected with the “rising-main,” before it
supplies the cistern.

=The Advantages of the Constant Service= may be thus summarised:—

(1) Owing to the absence of cisterns, the risks connected with stagnant
water, and with improper arrangement of overflow pipes, are obviated.

(2) The risk of suction into supply mains of external contaminations is
reduced to a minimum, since the pipes are never empty.

(3) The pipes are less liable to rust. Air in the presence of a little
moisture, causes rapid corrosion.

(4) There is an abundant supply of water in case of fire.

Of course, when there is a temporary stoppage of supply, as for
repairs, some of the dangers incurred by an intermittent supply will



=Properties of Water.=—When pure, water =is colourless=, or bluish
when seen in large quantity. It should be quite =inodorous=. If,
after keeping it for some time in a perfectly clean vessel, or if on
heating it a smell is developed, the water is bad. Its =taste= should
be pleasant and sparkling from the atmospheric gases dissolved in it.
Bitterness generally indicates the presence of sulphate of magnesium
(Epsom salts). Saltness is always a suspicious property, except in
water obtained in the neighbourhood of salt mines or brine springs, or
near the sea. It should be soft to the =touch=, and should dissolve
soap easily. It should be bright and =clear=, and contain no suspended
matters. Clear water is not necessarily pure, but turbid water is
always to be rejected; the only exception being the brownish-tinged
water from moors, which is not hurtful. In all other cases, printed
matter should be legible through at least 18 inches of water in a
clear glass cylinder. Thoroughly dissolved organic matter is less
dangerous than suspended; the turbidity of water is therefore of great
importance. But water may be bright and sparkling and apparently
perfectly clear, and yet highly dangerous. The most important of the
physical properties of water in regard to health are the absence of
smell and turbidity, and these can be ascertained by even the most
inexperienced. The chemical tests for the more important impurities are
given (pages 85 to 87).

The impurities of water may be classed under four heads—gaseous,
mineral, vegetable, and animal.

The gases ordinarily present in water cannot properly be regarded as
impurities, inasmuch as they are always present, and greatly increase
its palatableness. The dissolved nitrogen and oxygen bear to each other
the proportion 1·42 to 1; where sewage contamination occurs, the oxygen
will be diminished or disappear, owing to oxidation of the organic

The amount of carbonic acid gas in water varies greatly. It may be
considerable in chalk waters, and in contaminated well-water.

=Mineral Impurities.=—Mineral impurities are dissolved by water in
its course through the soil, and so will vary with the character of
the latter. 1. The water obtained from _granitic_ formations contains
very little mineral matter, often not more than two to six grains per
gallon. _Clay slate water_ is also generally very pure, as is the
water from hard _trap rocks_. 2. The water from _millstone grit_ and
_hard oolite_ is very pure, often containing only four to eight grains
per gallon, chiefly calcium and magnesium sulphate and carbonate. 3.
_Soft sand-rock waters_ usually contain thirty to eighty grains per
gallon of sodium salts, with a little lime and magnesia. 4. _Loose
sand and gravel waters_ vary greatly. They may be almost free from
mineral matter, or the solids may be more than seventy grains per
gallon, including much organic matter. 5. Waters from the _lias clays_
vary somewhat, but commonly contain a large quantity of calcium and
magnesium sulphates. 6. _Chalk waters_ generally contain from seven
to twenty grains of calcium carbonate, with smaller quantities of
other salts. 7. _Limestone and magnesian limestone waters_ differ
from the last, in containing more calcium sulphate and less calcium
carbonate, as well as much magnesium sulphate and carbonate in the
dolomite districts. 8. _Selenitic waters_ contain calcium sulphate
in considerable quantities. 9. _Clay waters_ usually possess the
characters of water from surface wells, and are objectionable. 10.
_Alluvial waters_ generally contain a large amount of various salts,
including the various calcium, magnesium, and sodium salts. 11.
_Artesian well water_ varies greatly in composition. It may contain
a large amount of sodium and potassium salts, or a small quantity of
iron, or calcium salts.

The commonest and most important mineral constituent of water is
calcium carbonate, next to this calcium sulphate. These two salts
are the chief causes of =hardness of water=. For practical purposes
as regards use in domestic matters and in manufactures, the most
important classification of waters is into _hard_ and _soft_. The
degree of hardness varies within wide limits—from rain-water, which has
no hardness at all, to the water from new red sandstone rocks which
sometimes possesses a hardness of 90 degrees; or wells in the gravel,
in which it may be as much as 152 degrees.

The following _classification of waters_, according to the degree
of hardness, beginning with the least hard and gradually increasing
in hardness, is from the sixth report of the Rivers Pollution
Commissioners:—1. Rain-water. 2. Upland surface. 3. Surface from
cultivated land. 4. River. 5. Spring. 6. Deep-well. 7. Shallow-well

Calcium carbonate is the most common cause of hardness, and the
hardness produced by it is remediable by boiling or chemical means.
Calcium carbonate (chalk) is rendered soluble in water, by the carbonic
acid contained in the latter, a double bicarbonate being thus formed.
The air contained in the interstices of the soil through which water
passes, often contains 250 times as much carbonic acid as ordinary air.
The water, in percolating through the soil, dissolves this carbonic
acid, and thus is able to take up a considerable amount of chalk.

The amount of hardness in any given water is expressed in degrees, one
degree being equivalent to a grain of calcium carbonate in a gallon
of water. =Clarke’s soap test= is employed to detect the amount of
hardness. It consists of a solution of soap of a known strength. Soft
water will form a lather at once with this; hard water will only form
a lather after all the calcium salt is neutralised. The amount of
Clarke’s solution required before a lather is produced, will give an
estimate of the amount of hardness.

 =To Determine the Total Hardness= take 70 c.c. of the water and place
 in a stoppered bottle. From a burette run in a sufficient quantity of
 the standard soap solution (of which 1 c.c. equals 1° of hardness), to
 produce a lather on shaking the water, which remains unbroken after
 standing five minutes. Thus, if 7·5 c.c. of the soap solution were
 required, the hardness is 6°·5, as 1 c.c. of the solution is required
 to produce a lather in soft water. The 6°·5 means 6·5 milligrammes of
 calcium carbonate in 70 c.c. or 6·5 grains in a gallon of the water.

 =To Determine the Permanent Hardness= boil 70 c.c. of the water in a
 flask for half-an-hour; allow the precipitated carbonates of calcium
 and magnesium to settle. Some of the latter will be re-dissolved.
 Carefully decant, and make up the liquid to the original 70 c.c.
 with distilled water. Filter through fine filter paper and estimate
 hardness as above.

The amount of soap wasted in consequence of the hardness of water is
very great. Thus, in the case of water of one degree of hardness, as
every gallon contains one grain of chalk, 7,000 gallons would contain
7,000 grains—that is, a pound. But every grain of chalk wastes 8 or
9 grains of soap; therefore, a pound of chalk, contained in 7,000
gallons, would waste about 8½ pounds of soap. But nearly all waters
are harder than this, and they not uncommonly possess a hardness of
20° or more. If the hardness be 20°, the waste would be 170 pounds of
soap. This quantity would be easily used annually in a family of seven
or eight persons, if we include the washing of clothes. The amount of
money thus wasted can be easily estimated.

Not only does soft water require less soap, but it is much more
suitable for making tea and soup, and for boiling meat and
vegetables—both time and fuel being saved. The reason why better tea is
made when a little carbonate of soda is added to the water is that the
chalk is by this means precipitated.

Carbonate of calcium is precipitated from water by boiling it; carbonic
acid being driven off, the neutral salt falls to the bottom of the
vessel. This is the origin of the “fur” inside kettles, which lessens
their conductivity to heat, and renders necessary a greater consumption
of fuel.

The chalk may also be removed by adding to the water, while still
in the reservoir, some milk of lime—that is, quicklime made into a
milky solution with water. This is done on a large scale at various
waterworks. The reaction may be expressed thus:—

Calcium bicarbonate + calcium oxide = calcium carbonate + calcium

The calcium carbonate, as it is precipitated, carries down with it
organic and other matters, thus clearing and purifying the water.

The hardness due to calcium sulphate is not removable by boiling. It
is, therefore, called =permanent hardness=, to distinguish it from the
_temporary hardness_ of chalk waters, which is removable by boiling.
It may, however, be partially removed by the addition of washing soda
to the water, as well as the nitrate and chloride of calcium which are
also present. The magnesium salts are not removable by boiling or
soda. This is shown by the fact that the “fur” inside kettles does not
usually contain magnesium salts.

The amount of hardness varies greatly in different waters. In the deep
wells in magnesium limestone, it varies from 14°-57°; in the deep
wells from chalk beds, it varies from 13° to 27° and may be higher.
In the water from Bala Lake, Wales, the temporary hardness is 0°·1,
the permanent hardness 0°·3; in the Loch Katrine water there is no
temporary hardness, 0°·9 permanent hardness; in the water from the new
red sandstone (Nottingham), the temporary hardness is 9°·6, permanent
10°·2; in a chalk spring at Ryde, temporary hardness 16°·7, permanent
3°·9 (Wanklyn). The total hardness in the metropolitan water supplies
from the rivers Thames and Lea, varies from 13°·2 (Southwark Company)
to 14°·6 (New River Company); in the Kent Deep Wells 20°·1; in deep
wells from the chalk at Brighton it varies from 12° to 13°. In all
these, the hardness is chiefly temporary.

The amount of permanent hardness is always great in water from clays,
as the London, Oxford, Kimmeridge, and Lower Lias clays; or in places
where there are large deposits of calcium sulphate, as at Montmartre,
near Paris (hence the name Plaster of Paris, given to desiccated
calcium sulphate). Water from fissures in the clay often contains,
also, a large amount of organic matter.

=Chlorides= are always present in small quantities in water. As a rule
the presence of more than 1 grain per gallon, _i.e._ ·7 parts per
100,000 of water, indicates contamination with some animal refuse,
unless the water is derived from new red sandstone, or brine springs,
or from the neighbourhood of the sea. This rule does not, however, hold
universally good. The absence or the presence of only a minute quantity
of chlorides indicates the probable absence of animal contamination;
but in exceptional cases waters of the highest organic purity may
contain more chlorides than the same bulk of sewage.

 =To determine the amount of Chlorine= take 70 c.c. of the water,
 add a few drops of solution of potassium monochromate (KCrO₄). From
 a burette run in gradually a standard solution of silver nitrate
 (of such a strength that 1 c.c. of the solution is equivalent to 1
 milligramme of chlorine). The silver solution forms milky chloride of
 silver (AgCl) by combination with the chlorine of the chlorides in the
 water. When all the chlorine is thus combined, the next drop of the
 silver solution forms a deep red tint with the chromate. The number of
 c.c.’s of the silver solution required to produce this effect, equals
 the number of milligrammes of chlorine in 70 c.c. of water, or the
 number of grains of chlorine in a gallon of water. To convert this
 into parts per 100,000, divide by 7 and multiply by 10.

 To express the amount of chlorine in terms of common salt (NaCl),
 multiply the parts per 100,000 of chlorine by 1·65.

=Nitrates= in any water are suspicious; but their import varies with
the circumstances under which they occur. A minute quantity of ammonium
nitrate is present in nearly all waters; and the water of deep wells,
especially of wells in the chalk, which, as a rule is perfectly free
from sewage, may be highly charged with nitrates. Nitrates, when
derived from sewage, represent a completely oxidised condition of
its nitrogenous matter. Crude sewage generally contains no nitrates.
=Nitrites= as a rule indicate more recent contamination, and therefore
greater danger than nitrates. The presence of more than a trace of
phosphates is a strong indication of contamination with sewage matter.

 =To determine the amount of Nitrites and Nitrates= the best known
 methods are by the indigo, the phenol-sulphuric, the aluminium, or the
 zinc-copper couple tests. For nitrites the metaphenylene-diamine test
 is employed (page 85). The following _qualitative tests_ will suffice
 for elementary work.

 =Nitrates.= An equal amount of a solution of brucine is added to the
 suspected water in a test-tube, then a little pure sulphuric acid is
 poured down the side of the tube. A pink zone is produced if nitrates
 are present in considerable amount.

 =Nitrites.= A few drops of each of diluted sulphuric acid and of
 metaphenylene-diamine solution give a red colour with water after
 standing for a few minutes, if nitrites are present.

=Lead= is an occasional contamination of slightly acid waters. The
purest and most oxygenated waters act most readily on lead; as
also those containing organic matter, nitrates or nitrites. Waters
containing chlorides also act on lead, the chloride of lead being
sufficiently soluble to produce poisonous symptoms. Upland surface
waters derived from moorlands in certain districts, _e.g._ around
Sheffield, have been found to be capable of dissolving considerable
lead from lead service-pipes. The water taken first from the tap in
the early morning is the most heavily charged with lead. Such waters
are very soft; but other moorland soft waters do not dissolve lead.
It is the water having a slightly acid reaction which possesses this
property. The source of this acid, whether sulphuric acid from the
products of combustion in a neighbouring town, or an organic acid,
is uncertain. The plumbo-solvent action of such water is greatest in
autumn, when the amount of acid is at its maximum. The property of
dissolving lead is removed by passing the water on a large scale over
filters of sand, spongy iron, chalk, or limestone. The addition of
a small quantity of carbonate of soda has the same effect. In such
districts the use of tin-lined iron pipes for domestic services has
been recommended, but these are liable to fracture when bent. Pipes
consisting of an outer case of lead and an inner pipe of tin with a
layers of asbestos between have also been placed on the market. (See
also page 68.)

Hard waters have the least action on lead; a coating of insoluble
carbonate of lead being formed on the interior of the pipe, which
prevents any further action. Thus the use of lead pipes for water
containing carbonates or sulphate, or calcium phosphate, is
comparatively safe. Hard water containing carbonic acid gas under
pressure will dissolve a small amount of carbonate of lead; this
explains the cases of lead poisoning from soda water which was formerly
supplied in syphon bottles with lead tubes.

Lead is dissolved much more easily by water if other metals are in
contact with it, as iron, zinc, or tin, galvanic action being thus set
up. Zinc pipes containing some lead are very dangerous, especially with
the distilled water used on board ships.

 =To determine the presence of lead in water=, place a given quantity,
 say 100 c.c. in a white dish, and stir with a rod dipped in a solution
 of ammonium sulphide; if the water becomes coloured, this is generally
 due to the presence of iron or lead. If the colour remains after
 adding a drop or two of hydrochloric acid, lead is present.

 =To determine the amount of lead=, a standard solution of lead acetate
 containing 1∕10 milligrammes of lead in 1 c.c., is made by dissolving
 ·183 gramme of crystallised lead acetate in a litre of distilled
 water. Place 100 c.c. of the water to be examined in a Nessler glass,
 acidify by a few drops of acetic acid; now add 1∕2 c.c. of a saturated
 solution of ammonium sulphide. A brownish-black discoloration is
 produced if lead is present. To a second Nessler glass, containing 100
 c.c. of distilled water, the same amounts of acetic acid and ammonium
 sulphide are added, and then a sufficient quantity of the standard
 lead solution is added, until the tints of the contents of the two
 Nessler glasses are identical. The amount of the standard solution
 added being known, we know the amount of lead in 100 c.c., and the
 amount per litre (1,000 c.c.) will be tenfold. Thus if 2 c.c. of the
 solution were required for matching colours, there were ·2 parts of
 lead per 100,000 of water, or ·14 grains per gallon.

=Traces of Iron= are sometimes present in water, giving it an
astringent taste. Such water is apt to turn brown; and tea made from it
is very dark.

=Organic Impurities.=—Organic impurities may be either vegetable or
animal, the latter being by far the most dangerous. The water from
moorlands is often brown, but this is not noxious. Growing plants,
again, may be beneficial to water, by absorbing dissolved organic
matter, and aiding its oxidation. Decaying vegetable matter is
objectionable in water, and may set up diarrhœa.

The most important organic impurity of water has an animal origin—from
sewage; the liquid or solid excreta (_i.e._ the urine or fæces) gaining
accidental access to the water. Besides sewage, the eggs of various
intestinal worms have been swallowed with water; and in a few cases,
even leeches. But whatever the source of the organic matter contained
in water, it contains nitrogen as an essential constituent; and tends
under the influence of warmth, and therefore especially in summer,
to undergo putrefactive changes, owing to the action of bacteria.
These split up the more complex molecules of organic matter into
simpler matter; ammoniacal compounds and salts, of which the most
important are nitrites and nitrates, being final products of their
activity. The detection of nitrates, and still more of nitrites, is
important, as they may indicate the occurrence of previous sewage
contamination. These products are quite harmless in water, except as
an indication that the water has been polluted, and that possibly a
certain proportion of the nitrogenous matter in the form of the complex
organic matter forming the germs of such diseases as enteric fever, may
still be present. Organic matter may be _suspended_ or _dissolved_,
the former being most dangerous to health. The germs or microbes
causing disease consist of suspended, _i.e._ particulate matter. The
amount of organic matter is determined by the amount of free ammonia
and albuminoid ammonia which are present (Wanklyn’s process), by
Frankland’s combustion process, or by Forschammer’s oxygen process; all
of which give indications, rather than an exact estimate of its amount.


 The following scheme of =qualitative examination= may be followed,
 when an immediate opinion is required as to a water. It can only be
 trusted when the examination shows pollution. The following results
 will be obtained, for instance, when a minute quantity of urine is
 added to a gallon of water.

 (1) The water has a faint odour.

 (2) Its colour is greenish yellow in bulk.

 (3) On adding a few drops of Nessler’s solution, a deep yellow colour

 (4) A few drops of an acid solution of permanganate of potassium
 become yellow when added to it.

 (5) Acidify some of the water in a test-tube with nitric acid, then
 add silver nitrate solution. Distinct cloudiness is produced, much
 greater than with pure tap water.

 (6) Addition of hydrochloric acid and barium chloride solution shows a
 much greater quantity of sulphates than the same quantity of tap water.

 (7) A quantity of the water evaporated in a porcelain dish over a
 Bunsen’s flame gives a white residue, which speedily turns brown, with
 a urinous odour.

 (8) Ignite the ash and add some nitric acid to oxidise it more
 completely. Then dissolve in distilled water, and add acid molybdate
 solution. A yellow colour, followed by a precipitate, indicates high
 phosphates and sewage pollution.

=The Complete Systematic Examination= is (_a_) physical, (_b_)
bacteriological, and (_c_) chemical. Of the =physical tests=, _colour_,
which should never be yellow or brown except for peaty water, is
important. _Taste_ is a somewhat uncertain guide, but any badly-tasting
water should be rejected. The _odour_ on heating to 80° F. in a closed
flask may indicate pollution. The degree of _hardness_ can be roughly
tested by rubbing between the hands. The absence of _turbidity_ is most
important, as suspended impurities are more dangerous than all others.
Printed matter should be legible through a column of 18 inches of water.

=Microscopally= the suspended matter in water which has been allowed to
settle should be examined. Particles of vegetable matter, _e.g._ fibres
of cotton, linen, cells of potato, or spiral cells of cabbage, are
important as indicating domestic impurities. Bits of wool, hair, wings
and legs of insects and epithelium may be discovered. The presence
of algæ, diatoms and desmids, or of water-fleas, cannot be held to
indicate pollution, as these are found in all running streams and in
many wells. The eggs and embryos of worms are much more serious.

=Bacteria= are almost invariably present in water. The majority of
these micro-organisms are harmless. But as they may number among them
the germs producing diseases like enteric fever and cholera, the
estimation of their number and particularly of any deviation from
the number usually present in a given water, and if possible the
detection of special disease-producing bacteria, are very important.
This method has been made more practicable since Koch’s method of
“plate cultivation” of bacteria was discovered. A small quantity of
the water to be examined (kept surrounded by ice until this test is
applied, to prevent multiplication of bacteria in the bottle), is
mixed with sterilised gelatine which has been melted over a water
bath. Then the mixture is spread in a thin layer on a glass plate and
allowed to solidify, having been covered to prevent atmospheric germs
from settling on the gelatine. The bacteria in the water thus become
fixed, each growing and forming “colonies” dotted over the plate.
These colonies can be recognised by their size and appearance, and by
sub-culturing according to recognised methods. The number of such
colonies, and the number of bacteria, from which, presumably, such
colonies sprang in 1 c.c. of filtered Thames water is usually much
below 100; in the water before filtration many thousands are present.
It has been suggested that no water should be regarded as wholesome
which contains more than 100 bacteria in each c.c.

This standard is, however, obviously arbitrary. Chalk water ought to
have a smaller number than this; river waters may have more, and yet
be wholesome. Everything depends on the character of the bacteria
found. The detection of the _Bacillus coli communis_, which is present
in sewage, and normally in the human intestine, is very suggestive of
contamination by sewage. The bacteriological method of examination of
water is still in its infancy.


 (1) The =total solids= are ascertained by evaporating a given quantity
 of the water to dryness, and weighing.

 (2) =Determination of Chlorine= (see page 81).

 (3) =Determination of Hardness= (see page 80).

 (4) The =Determination of Nitrites= is based on the reddish-brown
 colouration produced when an acid solution of metaphenylene diamine is
 brought into contact with a weak solution of nitrous acid. 100 c.c.
 of the water under examination are placed in a clean glass cylinder.
 Add 1 c.c. of H₂SO₄ solution (1 in 3), then 2 c.c. of metaphenylene
 diamine solution (5 grains in 1 litre of water with a little H₂SO₄
 added). Stir well with a glass rod. If a colouration is produced at
 once, a smaller quantity of water must be taken, and made up to 100
 c.c. with pure distilled water. The quantity of nitrous acid present
 is measured by introducing different fractions of a c.c. of the
 standard sodium nitrate solution[3] into similar glass cylinders.
 Each is then made up to 100 c.c. with distilled water, and the
 metaphenylene diamine solution and acid added as before. The colour
 develops slowly; time must, therefore, be allowed in matching.

 (5) The =Determination of Nitrates= can be conveniently made by the
 following method. When phenyl-hydrogen sulphate solution is poured
 upon a nitrate, and sulphuric acid is formed, picric acid is formed:—

  (C₆H₅)HSO₄ + 3 HNO₃ = C₆H₂(NO₂)₃OH + H₂SO₄ + 2 H₂O.

 The addition of free ammonia in excess forms yellow ammonium picrate,
 the intensity of the colour of which is an index of the picrate, and
 of the nitrate from which it was produced. (_a_) Evaporate 25 c.c.
 of the water under examination, and (_b_) 5 c.c. of standard KNO₃
 solution (containing 1 part N in 100,000) to dryness in two porcelain
 dishes over the water bath. Add 1 c.c. of phenyl-sulphate solution to
 each of these as soon as cool, stir well with a glass rod, then add 1
 c.c. distilled water to each dish and 3 drops of strong H₂SO₄. Next
 add 25 c.c. of water to each dish, and after heating for five minutes
 over the water bath, add solution of ammonia to each dish in excess.
 A yellow colour is produced in proportion to the amount of nitrate
 present. Transfer the liquids to glass cylinders, and dilute each to
 100 c.c. Take 50 c.c. of the solution showing the least colour, and
 dilute the other with distilled water, until it has the same tint.

 Supposing the 100 c.c. of the sample required to be diluted to 150

 Then the amount of N will be 150∕100 × 5∕25 = ·3 parts per 100,000.

 If the two solutions (_a_) and (_b_) when diluted have the same tint,
 then the

 Amount of N in the sample = 5∕25 = ·2 parts per 100,000.

(6) =Determination of Organic Matter.= Frankland’s =combustion process=
involves the use of delicate and costly apparatus, and is seldom
employed. In this process the organic carbon is evolved as carbonic
acid, and the nitrogen as such.

=Wanklyn’s ammonia process= is based on the reduction of organic
matter to ammonia. Part of this ammonia, =free or saline ammonia=, is
simply combined with carbonic, nitric, or other acids, or is easily
derived from the urea of urine, CH₄N₂O + 2H₂O = 2(NH₄)₂CO₃. Another
part is only set free when the water is boiled with a strongly alkaline
solution of permanganate of potassium. This is called the =albuminoid

In carrying out this method, a retort is taken, and after having been
washed out, first with a little sulphuric acid, and then with some of
the water to be analysed, 500 c.c. of the latter is put in, and the
retort is connected with a condenser, and distillation begun; 50 c.c.
of the distilled water is collected in a cylindrical glass tube called
a Nessler glass. To this 1½ c.c. of Nessler’s reagent (mercuric
iodide dissolved in a solution of potassic iodide and made alkaline by
potass) are added. A rich brown colour is produced, if any ammonia is
present in the distillate. The amount of ammonia in the distillate is
determined by exactly imitating its colour by adding a known quantity
of a standard solution of ammonium-chloride to 50 c.c. of ammonia-free
distilled water, and then Nesslerising as before. Each c.c. of the
dilute standard ammonium chloride solution is equivalent to ·00001
gramme of ammonia (NH₃).

If the first 50 c.c. of water distilled over gives only a slight
colouration with the Nessler solution, no more water needs to be
distilled over for free ammonia. If more is present, two more 50 c.c.’s
must be distilled over, and the amounts of the standard solution
required for imitating the test in each Nesslerised 50 c.c. added
together. Thus, if 2 c.c. were needed. This

 = ·00002 grm. NH₃, which is contained in 500 c.c. of the water

 = ·00002 × 200 = ·004 parts saline NH₃ in 100,000 of water.

The free ammonia having been distilled over, 50 c.c. of an alkaline
permanganate solution (containing 8 grammes KMnO₄ and 200 grammes
of NaOH in 1100 c.c. of distilled water, boiled until the bulk is
reduced to 1,000 c.c.) is poured into the retort, and distillation
is begun again. Three successive 50 c.c.’s of water are collected,
and then the distillation stopped. Each of these is Nesslerised, and
the tint imitated as before with standard ammonia solution. The three
amounts of ammonia thus found to be present are added together; and
when multiplied by 200, we obtain the amount of albuminoid ammonia in
100,000 parts of water. This test is universally employed by water
analysts along with the next test.

The amount of =Oxygen Absorbed= from permanganate of potassium is
regarded as an approximate test of the amount of organic matter in
water. Qualitatively this forms a favourite method of testing the
purity of water. Two glass cylinders are taken, one filled with
distilled water, one with the water to be tested. To each is added a
given small amount of an acid solution of permanganate of potassium.
The distilled water to which permanganate has been added will retain
its pink colour; while, if the water being tested is very impure,
it will speedily become decolourised. The rapidity and degree of
decolourisation are a rough test of the amount of impurity. A rapid
decolourisation proves the presence of organic matter having an animal
origin, or of sulphuretted hydrogen, iron, or nitrites. Sulphuretted
hydrogen is rarely present, and can be easily recognised by its smell;
iron or nitrites are readily distinguished by their appropriate tests.
In the absence of these, the rapid discolouration is an indication of
animal contamination.

=To Determine the Amount of Oxygen Absorbed=, two glass-stoppered
bottles, each holding about 350 c.c. are required. Into one, 250 c.c.
distilled water, and into the other the same amount of the water under
examination are placed. To each are then added 10 c.c. of standard
permanganate of potassium solution[4] and 10 c.c. of a standard pure
25 per cent sulphuric acid solution. The two bottles, after being
shaken, are placed in a water-bath at 27°C for four hours. At the
end of this time add a few drops of potassium iodide solution to each
bottle. The pink is now replaced by a yellow colour.[5] A standard
thiosulphate solution (Na₂S₂O₃, 5H₂O)[6] is placed in a burette. From
this the thiosulphate solution is run into the control bottle until the
yellow colour almost disappears. Now a few drops of starch solution
are added, and a blue colour is produced. The thiosulphate is then
added cautiously until all the blue colour disappears. The amount of
thiosulphate necessary for this is read off on the burette. The same
process is repeated with the bottle containing the sample of water. The
starch acts as an indicator. The amount of iodine liberated is an index
of the amount of permanganate in the water, which has not been used up
by its impurities. The amount of iodine liberated is measured by the
amount of thiosulphate required to decolourise the solution. Thus—

 2 Na₂S₂O₃ + I₂ = 2 NaI + Na₂S₄O₆.

Suppose that 20 c.c. of thiosulphate solution were required to
decolourise the iodine liberated in 250 c.c. of a sample of water,
while the distilled water required 25 c.c. Then 25 c.c. thiosulphate
represents 10 c.c. of the permanganate solution = ·001 grains of
available oxygen.

 25-20 = 5

 As 25 c.c. = ·001 grm. O, 5 c.c. = 5∕25 of ·001 = ·0002 grm.

  This is the amount of O absorbed by 250 c.c. of the sample.

  Therefore     „       „     „       100,000      „       = ·08 grm.

It is usual to make a similar determination of the amount of oxygen
absorbed in fifteen minutes.

The =Interpretation of Results= of analysis is more difficult than
the analysis. A single analysis may be misleading, unless the source
of the water is known. Constancy in composition or analysis is almost
as important a criterion of purity as the actual character of the
constituents. A knowledge of the source is essential in interpreting
results of analysis, as the chemical composition of water varies with
its source. The following rules are only approximately correct, and
are subject to the above general considerations. The _total dissolved
solids_ in river-water are usually 10 to 30 parts in 100,000. Shallow
well-water may contain from 30 to 200 parts or even more, and deep
well-water from 20 to 70 parts.

_Saline Ammonia_ in water is commonly of animal origin, ammonia (NH₃)
being one of the first products of decomposition of nitrogenous animal
refuse. Upland surface water usually contains about ·002 parts per
100,000, but it may reach ·008 or more if the land over which the
water passes has been manured. Shallow well-water may be free from
ammonia, or this may be very excessive in amount. Deep well-water may
contain no ammonia or any amount up to ·1 per 100,000. Its presence is
suspicious if the albuminoid ammonia is above a trace, or if the oxygen
absorbed is appreciable in amount. Generally water is suspicious if
saline ammonia is up to ·01 per 100,000. _Albuminoid Ammonia_ indicates
the amount of organic nitrogenous matter present in the water. It
should not exceed ·005 parts per 100,000, while at the same time the
saline ammonia should not usually exceed ·01 per 100,000. For _Oxygen
consumed_ the following table of the weight of oxygen required for
100,000 parts of water is given by Clowes and Coleman:—

  │ _Water of_         ├─────────────────────┼─────────────────────────┤
  │   _Great purity_   │Not exceeding ·1     │Not exceeding ·05        │
  │   _Medium purity_  │From ·1 to ·3        │From ·05 to ·15          │
  │   _Doubtful purity_│From ·3 to ·4        │From ·15 to ·20          │
  │      _Impure_      │Exceeding ·4         │Exceeding ·20            │

The presence of more than 1 and still more so of 2 grains of _Chlorine_
per 100,000 of water is most suspicious, except in saline districts.
_Nitrites_ if present in an appreciable quantity indicate comparatively
recent contamination by sewage. In deep well-water they may be produced
by deoxidation of nitrates. _Nitrates_ in upland surface waters should
not be equivalent to more than ·03 of N. per 100,000; in shallow
well-waters the amount varies greatly; in deep well-waters it may be
excessive. As a rule it ought not to be equivalent to more than 5 parts
of N. per 100,000 of water; but the significance of nitrates depends
greatly on the source of the water and on the amount of the other
constituents present.

Chemical analysis alone cannot ascertain the safety of a given drinking
water. A minute amount of impurity inappreciable to analysis may be
competent to produce disease; while another water may be drunk with
impunity, which contains considerable organic matter. Chemical analysis
“can tell us of impurity and hazard, but not of purity or safety”
(Buchanan). An accurate opinion as to the character of a drinking
water can only be expressed when one knows the amount of each chief
constituent (as above), and whether these amounts deviate from the same
water at other times or from other waters in the vicinity.



=Origin of Impurities of Water.=—Parkes classifies impurities of water

1. =Those Received at the Source.=—The character of water varies with
the geological structures through which it has passed; with its origin
from the subsoil or cultivated land, or deep wells, or graveyards, or
near the sea, etc. It is a mistaken policy to commence with an impure
water and proceed to purify it; though communities supplied from rivers
may be compelled to submit to this. They must then insist on the most
stringent measures of purification (see p. 96). Inorganic impurities
are of much smaller consequence as regards health than organic; hence
the great advantage of deep well-water over river water. It has been
suggested, however, that when deep well-water becomes polluted, it is
more dangerous than equally polluted river-water, because in the latter
the normal bacteria of water are more abundant, and possibly interfere
with the continued life in water of disease-producing bacteria. This
statement is unproved; and if correct, is rather an indication for
further precautions being taken to prevent access of pollution to deep
wells, than in favour of the continued use of river-water.

2. =Impurities of Transit from Source to Reservoir=, acquired during
the flow in rivers, canals, or other conduits. These impurities have
been broadly divided by the Rivers Pollution Commissioners into
“=sewage=” and “=manufacturing=;” the former including the solid and
liquid excreta, the house and waste water, etc.; the latter including
the refuse from manufacturing processes, as from dye and bleaching
works, tanneries, etc.

3. =Impurities of Storage=, whether in wells, reservoirs, or cisterns.
Organic impurities are commonly received at this stage. A well, for
instance, drains the soil around it in the shape of an inverted cone,
with a very broad base, unless the entrance of water from its sides is

4. =Impurities of Distribution.= Lead, and occasionally other metals,
are dissolved by certain waters. If the pipes are left empty, as with
an intermittent supply, sewage may be drawn into them; in a few cases
coal-gas has found its way into the water pipes (page 76).

=Effects of Impure Water.=—1. =Effects of Mineral Impurities.=
_Suspended Mineral matters_ in unfiltered water occasionally produce
diarrhœa. The hill diarrhœa of some parts of India has been traced to
water containing fine mica particles in suspension.

=Hard water= is said by some to be hurtful, but the salts causing
hardness are probably innocuous when not amounting to more than 12 or
16 grains per gallon. Persons in the habit of drinking hard water find
soft water unpalatable. Hard water has been thought to favour gout and
calculus (stone), but this is not so. The salts producing permanent
hardness are said to be injurious, producing indigestion, but this is
doubtful in the amounts ordinarily drunk.

=Goitre=, a swelling of the thyroid gland in the neck, is often
associated with the use of drinking water from magnesian limestone
formations; but that any kind of excessively hard water causes goitre
is very doubtful.

=Lead= dissolved in water may produce serious and lasting ailments, and
they are often present for a long time before their cause is detected.
The amount of lead capable of producing poisonous symptoms has been as
little as 1∕100 grain per gallon of water (Dr. Angus Smith). According
to De Chaumont, 1∕10 grain per gallon, that is 1 part in 700,000 is
usually required to produce such symptoms. In the well-known case of
the poisoning of Louis Phillippe’s family at Claremount, there was
7∕10 grain of lead in a gallon of water; and this affected 34 per
cent. of those who drank it. The symptoms produced by lead poisoning
are those of indigestion, accompanied by colic; a blue line at the
junction of the gums with the teeth; “wrist drop,” a paralysis of the
muscles of the forearm, or some other paralysis; and if the poisoning
is continued, attacks of gout, followed by its usual consequences,
chronic kidney disease. The latter affections chiefly occur when the
poisoning is continued for a long time, as in the case of painters or
type-setters: poisoning from water is generally discovered before any
other than dyspeptic symptoms and colic are produced.

The presence of traces of iron in water may give it a slightly
astringent taste; and such water is liable to cause headache and

2. =Effects of Vegetable Impurities.=—Living plants are
unobjectionable, but decomposing vegetable matter may produce diarrhœa
and other severe symptoms.

3. =Effects of Animal Impurities.=—Animal impurities of water are by
far the most important from a sanitary point of view. They are most
commonly derived from leaky drains or cesspools, or from surface
accumulations of filth. The quality of the contamination is more
important than its quantity; and this will explain why water containing
a large amount of sewage may be drunk for a prolonged period with
impunity, while at another time the least trace, if it contain the
active germs of disease, will lead to serious mischief.

Suspended animal impurities are much more dangerous than those
completely dissolved. Hence the examination of the colour and
turbidity of drinking water is very important. Fæcal contamination is
by far the most dangerous of all, and chiefly so when it is derived
from a patient suffering from some communicable disease, like enteric
fever or cholera.

=Certain Parasites= occasionally are swallowed with water in the form
of embryo or egg. The liver fluke, round worm, and less frequently
other kinds of entozoa have been introduced in this way. The occasional
swallowing of small leeches has occasionally given rise to hæmorrhage.

=Diarrhœa= may be caused by animal contamination of water. It most
often occurs in summer, when all the circumstances are favourable to
active fermentative changes. The summer diarrhœa of infants is caused
by similar changes in milk or other foods. The presence of fœtid gases
in water may lead to diarrhœa. This may occur when the overflow pipe of
a cistern opens into the soil pipe or into the trap of the W.C.

=Dysentery=, like cholera and enteric fever, may be propagated by water
contaminated with the stools of a patient suffering from the same

=Malaria or Ague= has been stated to be caused by the water of
malarious marshes. The evidence on this point requires revision,
in view of the part which the mosquito is now known to play in the
propagation of this disease (pages 282 and 307).

=Enteric= (_otherwise called Typhoid_) =fever= is most often due to the
drinking of water contaminated with sewage.

The balance of evidence is in favour of the view that in order to
produce enteric fever water must be contaminated with the stools
or urine of a patient who has suffered from this disease. Numerous
instances are on record in which villages, the inhabitants of which
drink sewage-contaminated water, have remained free from enteric
fever, until a patient suffering from it has come to the village,
when the spread by water has been very rapid. Occasionally no known
contamination from a case of enteric fever has preceded the outbreak
of this disease which has been caused by sewage-contaminated water. It
must be remembered on this point that the urine of an enteric fever
patient may occasionally contain large numbers of the bacillus causing
this disease for several months after the patient is well (page 301).

The contamination of water with sewage may occur in various ways. In
country places surface wells and small streams commonly supply the
drinking water, and these are frequently contaminated. The illustration
(Fig. 9) shows the percolation of excretory matters from an out-door
closet through the porous gravel, into a neighbouring well; the result
being an epidemic of enteric fever among those who drank the water of
the well. Alterations in the level of the subsoil water are sometimes
followed by an outbreak of enteric fever (p. 70). A sudden fall of rain
occurs, and the excess of water in the soil absorbs the soakings from
country privies or cesspools, and carries them into the nearest well.
The percolation of tainted water through a considerable tract of land,
possibly along fissures, is sometimes insufficient to purify it, as
proved by a remarkable epidemic in the small village of Lausen, in

In other cases sewage gains access into leaky water-pipes. Formerly
contamination was occasionally due to improper connection between the
overflow pipe of the cistern and the soil-pipe, or to the water-closet
being flushed by a pipe directly connected with a water-main (as
in the Caius College outbreak at Cambridge), or connected with the
drinking-water cistern (page 76).

Milk may, by the admixture of water, become contaminated with enteric
matter, and produce widespread epidemics. Where the water is very
impure, the small amount used in washing cans may suffice to cause

_Cholera_ was first proved by Dr. Snow, in 1849, to be due to the
specific contagium of cholera gaining an entrance into drinking water.
This contagium is derived as in enteric fever from the intestinal
evacuations, the urine, and the vomit of patients suffering from the
same disease.

[Illustration: FIG. 9.]

The close connection of the spread of cholera with an impure water
supply has been repeatedly shown in this country. The cholera epidemic
of 1854 was very severe in the southern districts of London. At that
period these districts were supplied with water by the Southwark and
Vauxhall Company, deriving its water from the Thames at Battersea,
and by the Lambeth Company, having its intake at Thames Ditton, where
the water was purer. The two companies were acting in rivalry, so
that in many streets their mains ran side by side; and houses in the
same street similar in all other respects, received a different water
supply. An investigation of the distribution of cholera in these
districts gave the following results:—

                                    POPULATION  CHOLERA    CHOLERA DEATHS
                                    IN 1851.    DEATHS IN  PER 10,000
                                                14 WEEKS.  OF POPULATION.

  Houses supplied by Southwark Co.  266,516      4,093          153

     „      „        Lambeth Co.    173,748        461           26

The facts, when examined in detail, brought out still more strikingly
the exemption of the houses supplied by the Lambeth Company; the
infection picking out in a given street the houses supplied by the
Southwark Company. The great epidemic of cholera at Hamburg in 1892
proves the same point. Hamburg, Wandsbeck and Altona are three towns
adjoining each other, and really forming one large community; but while
Hamburg suffered terribly, the two other towns had no cases of cholera,
except the few that were brought into them. In all respects except
water-supply the conditions were alike; but Wandsbeck obtained filtered
water from a lake, Altona obtained filtered water from the Elbe below
the town, while Hamburg was supplied, previous to the epidemic, by
unfiltered water from the Elbe just above the town.

=Diphtheria= and scarlet fever have never been traced to polluted water.

=Effects of an Insufficient Supply of Water.=—The influence on personal
health is most baneful. Water is used sparingly for purposes of
cleanliness, with the necessary results that cutaneous diseases become
more common, and the whole body suffers; the linen is imperfectly and
infrequently washed; the house becomes dirty; drains are imperfectly
flushed; the streets are not cleaned; and the whole atmosphere becomes
loaded with impurities. According to Parkes, it is probable that the
almost complete disappearance of typhus fever from civilized and
cleanly nations, is not merely owing to better ventilation, but also to
more frequent and thorough washing of clothes.

Insufficient cleansing of the surfaces of streets and of sewers, owing
to a deficient supply of water, has a very important influence on
the spread of enteric fever and epidemic diarrhœa. A heavy fall of
rain often causes a rapid diminution in the prevalence of the latter



When a public water-supply is provided, it may reasonably be expected
to be furnished pure and fit for use; but this, occasionally is not so.
The reports, for instance, of the condition of the London Water Supply,
occasionally show that it is turbid and contains a slight excess of
organic matter. This is especially the case when, after heavy rainfall,
storm-water is brought into the reservoirs, and owing to deficient
storage, sufficient time is not allowed for deposit. Rain-water always
and other waters frequently require to be purified before use.

=Methods of Purification.=—The only certain way of obtaining pure water
is by =Distillation=; but this plan is scarcely applicable to water
on a large scale. Furthermore distilled water is not so palatable as
ordinary water. The distillation of water is more especially required
on board ship, during long voyages. It should be followed by the use of
some measure to secure efficient aeration.

2. =Boiling water= serves to remove the temporary hardness, and the
chalk carries down with it a large proportion of any organic matter
that may be present. Boiling deprives the water of its dissolved gases,
and renders it flat; it is desirable, therefore, to aerate it by
filtration or from a gazogene after boiling. All the microbes which are
known to produce disease are destroyed by efficient boiling. Certain
putrefactive microbes are more persistent of life, owing to the fact
that they form spores, which are not killed at the temperature of
boiling water. Tyndall showed that by boiling the liquid containing
these spore-forming microbes on three successive days, thus giving time
for the spores to develop into less resistant microbes, they could be
effectually destroyed. Boiled water will not cause enteric fever or
cholera, the two chief water-borne diseases.

3. The exposure of water in divided currents to the air by passing it
through a sieve has been proposed as a means of purifying water, but
it is inefficient when trusted to alone. Plants in reservoirs help to
absorb organic matter; and fish, by destroying small crustaceans, have
been found useful. Hard waters do not bear exposure to light, as a
thick green growth of chara occurs, which may block pipes, and give a
bitter taste to the water.

4. =The Addition of Chemical Substances.=—(1) _Clarke’s process_
consists in adding milk of lime, _i.e._ an emulsion of quicklime with
water, to the water in the reservoir on a large scale. By this means
calcium carbonate is precipitated, but no effect is produced on calcium
and magnesium sulphates and chlorides. The hardness of the Thames
water can thus be reduced from 16° to 3° or 4° (_Clarke’s scale_). The
calcium carbonate carries down with it suspended and possibly dissolved
organic matter. In the _Porter-Clarke process_ lime-water, _i.e._ milk
of lime diluted, and the excess of lime separated by settlement or
filtration, is mixed with the water to be purified, the water being
freed from the precipitated calcium carbonate either by subsidence or
by being forced through a filter of stretched canvas.

(2) _Carbonate of Soda_ added to boiling water throws down calcium
carbonate, and possibly lead if present. Much less is required when
added to boiling than to cold water. Maignen’s process consists in
adding _anti-calcaire_ powder, containing chiefly carbonate of soda,
lime, and alum.

(3) _Aluminous salts_ are very effectual in removing suspended organic
matter, if the water contains calcium carbonate. On the addition of
alum, calcium sulphate and aluminium hydrate are formed, both of which
fall to the bottom, carrying with them other impurities. The amount of
alum required is about 6 grains per gallon of water. If the water is
not hard, a little calcium chloride and carbonate of soda should be put
in before the alum is added, in order that a precipitable substance may
be formed.

(4) _Potassium permanganate_ readily removes the offensive smell of
stagnant water, but it gives a yellow tint to the water. The addition
of a little alum will help to carry down the decomposed permanganate.

(5) _Perchloride of Iron_, in the proportion of 2½ grains to a
gallon of water, has been found to completely purify water from finely
suspended organic matters and clay.

(6) More recently, other substances, such as _iodine_ and _hyposulphite
of soda_, have been recommended. These are supposed to act by
sterilizing the water, and iodine in suitable quantities undoubtedly
effects this.

Chemical processes for the purification of water, with the exception
of the softening process, are not to be recommended for general use.
Efficient filtration, or boiling, is safer than chemical treatment;
and it would only be justifiable to trust to the latter, when, as in
a military campaign, an attempt at purification was necessary, and no
means were available for filtering or boiling water.

7. =Filtration.=—The object of filtration is to remove the impurities
of water. The most dangerous impurities are suspended in it, especially
the microbes causing infectious diseases. Hence the most perfect filter
is the one which most completely prevents the passage through it of
microbes. If the water supply is pure, domestic filtration is not only
useless, but likely to do more harm than good. This is true for such
upland surface waters as those supplied to Liverpool, Glasgow, and
Manchester; for such deep well-water supplies as those of Brighton
(deep chalk), of Nottingham (new red sandstone), and others, when
pumped from wells remote from inhabited houses. For upland surface
waters known to attack lead pipes, filtration through charcoal or
spongy iron may be advisable; for river water, filtration through a
germ-proof filter is best.

Filtration =on a large scale= is generally carried on as follows:—A
preliminary step consists in collecting the water into settling
reservoirs, wherein the more bulky substances subside. The water is
then filtered through beds of gravel and sand, containing perforated
tubular drains below, into which the filtered water flows. The drains
are covered by a bed of gravel about 3 feet deep, over which is spread
a layer of sand about 1½ to 2 feet deep. Sharp angular particles
of sand are the best; and the gravel should gradually increase in its
coarseness as it descends.

The effect of this filtration is chiefly _mechanical_; it separates
any suspended matter, whether organic or inorganic. A certain amount
of _biological_ action possibly also takes place. Piefke found that a
perfectly cleaned and sterilised filter when first used, increases the
microbes in water, instead of decreasing them. Gradually a gelatinous
layer of slimy matter is formed on the top of the sand; the water now
filters through much more slowly, but it gradually becomes freer from
microbes, these being intercepted by the slimy layer. It is important
that this layer should not be disturbed by too rapid or forced
filtration, and that when the surface layer requires to be removed,
because the filter has become impervious, time should be allowed
for another thin film to form before the filtered water is again
utilised. Koch concluded that the rapidity of filtration should never
be allowed to exceed 100 millimetres (about 4 inches) per hour; and
that the number of microbes per c.c. in the filtered water should never
exceed 100. Some oxidation of organic matter, as well as detention
of microbes, may take place during the filtration of water, nitrates
being formed by the vital activity of certain “nitrifying” microbes in
the filter. (On nitrification, see pages 195 and 274.) P. Frankland’s
observations show that the number of microbes in Thames water is
reduced by filtration through sand and gravel beds, as practised by the
London Water Companies, so that only 3·4 per cent. of those originally
present remained. He also concludes that the majority of the microbes
present in filtered water are derived from post-filtration sources.
Thus the number is greater in tap-water than in water derived from near
the reservoirs.

Other materials besides sand have been used for filtration on a large
scale, but none with proved success.

=Domestic Filtration= ought, as already explained, not to be needed,
but circumstances often arise in which the public supply is open to
suspicion, and a second domestic line of defence against infection
through the water supply is desirable. When this is so, the form of
filter which will best protect the household is one attached to the
house-tap, so that all drinking-water is perforce filtered. When
filtering involves the transfer of water from the tap to the interior
of the filter, opportunity is left for carelessness or forgetfulness.
The one essential point of a domestic filter is that it will prevent
the passage through it of microbes. Every filter must be tested from
this standpoint.

On this point the experiments of Woodhead and Cartwright Wood are
conclusive. They first of all experimented on various filters with fine
artificial ultramarine containing particles 16 µ to 0·6 µ or even less
in diameter in suspension; and milk containing granules and globules of
fat 0·5 µ to 30 µ or more in diameter, freely diluted with water.

  │                     │TIME IN MINUTES│PRESENCE OR   │PRESENCE OR    │
  │                     │REQUIRED FOR   │ABSENCE OF    │ABSENCE OF MILK│
  │                     │FILTRATION OF 1│ULTRAMARINE IN│IN FILTRATE    │
  │                     │PINT OF WATER. │FILTRATE.     │               │
  │_Silicated carbon    │               │              │               │
  │   filter_           │ 68            │++            │+++            │
  │_Carbon filter_      │ 18            │ +            │+++            │
  │_Maignen’s Filtre    │               │              │               │
  │  Rapide_            │  4            │ 0            │ ++            │
  │_Spongy iron filter_ │ 14            │ 0            │+++            │
  │_Pasteur-Chamberland │               │              │               │
  │   filter_           │420            │ 0            │  0            │
  │_Berkefeld filter_   │140            │ 0            │  0            │

The number + indicates the relative amount of the experimental
substances that made their way through the filtering medium.

Experiments were then made with the actual microbes of certain
infectious diseases, and it was found that certain filters allow these
to pass. Thus a silicated carbon filter allowed 1,000 out of 15,000
typhoid bacilli suspended in water to pass through its substance;
a manganous carbon filter allowed 600 to 800 out of 10,000 cholera
vibrios to pass through; Maignen’s filter on the second day of
experiment allowed 150 out of 5,000 cholera vibrios to pass through;
Lipscombe’s charcoal filter experimentally only reduced typhoid bacilli
from 20,000 to 5,000; the magnetic carbide filter only reduced them
from 20,000 to 10,000; the spongy iron filter from 20,000 to 3,000;
while, on the contrary, the Pasteur-Chamberland and the Berkefeld
filter completely stopped all microbes and produced a sterile water.
(As to these two, see page 98.)

Of the materials enumerated =animal charcoal= was formerly regarded
as an excellent filtering medium. It is capable of oxidising organic
matter dissolved in water, but so far from sterilizing water, it
favours the growth of microbes in it. Water filtered through charcoal,
after the first few days of use of the charcoal, deteriorates, as the
charcoal yields up impurities to it.

=Manganous Carbon= consists of animal charcoal and black oxide of
manganese mixed with oil, and heated strongly together out of contact
with the air. The oxidising power of the carbon is said to be thus
greatly increased. It shares the objections to carbon.

=Silicated Carbon= consists of 75 per cent. of charcoal and 22 per
cent. of silica, with a little oxide of iron and alumina. It is not an
efficient filtering medium.

Spongy iron is prepared by the reduction of hæmatite ore with fusion,
so that the iron is obtained in a porous and finely-divided condition.
The Rivers Pollution Commissioners found spongy iron to be “a very
active agent, not only in removing organic matter from water, but
also in materially reducing its hardness, and otherwise altering its
character.” It is a powerful oxidising agent, some of the water being
decomposed, and hydrogen set free, and the oxygen acting upon any
organic matter present. It also removes lead from water. As already
seen, it does not, however, fulfil the primary object of water, by
depriving it of any microbes contained in it.

=Magnetic carbide of iron= is obtained by heating hæmatite ore with
sawdust. Its action is similar to that of spongy iron.

The =Pasteur-Chamberland filter= consists of a cylinder of unglazed
fine porcelain made from a well-baked Kaolin of a certain degree of
porosity and hardness. (Fig. 10.)

The water passes through the porcelain from without inwards, and with
the pressure of 1½ to 2½ atmospheres which is usually present in
the pipes of a water-service, passes through at the rate of about three
quarts per hour. The filter can easily be cleaned by brushing it in a
stream of hot water, or by subjecting to the heat of a Bunsen burner.
The filtration is entirely mechanical, the filtered water being quite
freed of microbes. No chemical action takes place.

[Illustration: FIG. 10.


A.—Outlet of filtered water. B.—Pasteur tube. C.—Metal tube containing
unfiltered water. D.—Unfiltered water delivered through tap. ]

The =Berkefeld filter= is cylindrical like the Pasteur-Chamberland
filter, and is used in the same way. It is made of infusorial earth,
which is soft and friable and liable to break. The cylinder becomes
gradually worn thin by cleaning, and it then ceases to filter
efficiently. Its sole advantage over the Pasteur-Chamberland filter is
the more rapid rate of filtration; and against this is to be set the
greater liability to fracture and the lack of continuance of efficient
filtration. Woodhead and Wood in the report already quoted, state:
“The Berkefeld filter appears to have the largest pores among the
efficient filters, as is evidenced by the fact that the water organisms
were not apparently weakened, that more species of organisms appeared
in its filtrate, and that lowering the temperature to 11° C. did not
prevent their appearance. The Pasteur-Chamberland filter, on the other
hand, at 11° C. was able to give an apparently sterile filtrate for a
prolonged period.” More recent experiments have shewn that pathogenic
(disease-producing) microbes contained in water after awhile grow
through the substance of a Berkefeld filter, and that this does not
happen with a Pasteur-Chamberland filter. The latter is therefore

In determining the number of bougies required for any filter to secure
a given amount of pure water, it is necessary to calculate on the basis
of the output after several weeks’ use, not on the original output. If
this is done, pure water will be secured without disappointment as to
the amount supplied.



An abundant supply of fresh air is necessary at all times. And yet its
importance is commonly ignored in practical life. Strenuous efforts
are made to ensure a supply of food, and water is commonly filtered or
otherwise purified before drinking; but many are content to live in an
impure atmosphere, which hardly suffices for the preservation of life,
and certainly not of health. Deprivation of food, or even of water,
only kills after several days or weeks; deprivation of air kills in a
few minutes. Only about three pints of water are required daily, while
at least 1,500 gallons of air are necessary every day for carrying on
the vital functions.

=Composition of Air.=—The air constitutes a gaseous ocean in which
we live, as fishes live in water. In virtue of its weight, it exerts
a pressure of about 15 lbs. on every square inch. This pressure is
usually measured by the _barometer_, and is equivalent on an average to
that of a column of 30 inches of quicksilver. (See page 331).

Chemically, air consists of a mixture of various gases and vapours.
These are chiefly =Oxygen= and =Nitrogen=; but in addition, there are
minute quantities of carbonic acid, argon, hydrogen, water vapour,
ammonia, ozone, and suspended matters.

The oxygen and nitrogen exist, in the proportion by volume of 20·9 of
oxygen to 79·1 of nitrogen, or of 23·16 grains of oxygen to 76·84 of
nitrogen, by weight.

These two gases do not exist in chemical combination, but mechanically
mixed. This is proved by the fact, that they do not exist in air in the
proportion of their combining weights, or any multiple of these; that
the proportion varies slightly at different parts; and that the air
which is dissolved in water does not contain the nitrogen and oxygen
in the proportion 4 to 1 (as in the atmosphere), but in the proportion
1·87 to 1. This means that oxygen, being more soluble in water than
nitrogen, has dissolved in a larger proportion; as it certainly would
not have done, had the oxygen and nitrogen been chemically combined.
The oxygen dissolved in water supplies fishes with the necessary oxygen
for their respiratory processes. Similarly the oxygen in the atmosphere
is its most essential constituent, being required in all processes of
oxidation (_i.e._, combustion), whether in living organisms or in the
inanimate world. Nitrogen serves as a diluting agent. It is incapable
of supporting life alone; and many of the fatal accidents which have
occurred through men descending deep wells without first testing, by
means of a lit candle held well below them, the quality of the air near
the bottom, have been due to an accumulation of nitrogen in the well.

=Ozone= is a condensed form of oxygen, which is present in minute
quantities in pure air, and especially during a thunder-storm or after
a fall of snow, and in the air near the sea. In it three volumes of
oxygen are condensed so as to occupy two volumes. In this condensed
condition it has powerful chemical affinities; often oxidising
substances which oxygen cannot attack. It is generally absent from the
close air of towns and dwelling houses, having been used up to oxidise
the organic matter present in these places. Air without it is said to
be “devitalised”; and ozone has been described as the scavenger of the

Ozone can be produced by hanging a piece of moist phosphorus in a room;
and it is stated by Dr. Daubeny, that part of the oxygen given out by
plants, especially by scented flowering plants, is in the condition
of ozone. A small quantity is produced when an electrical machine is
worked; its presence is evidenced by a peculiar smell (the name ozone
is derived from the Greek word for smell).

 =Test of Ozone in Air.=—Traces of ozone in air are detected by
 exposing strips of blotting paper moistened with a mixture of a
 solution of potassic iodide and starch. If ozone is present, the
 paper assumes a blue tint, due to the liberation of iodine, and its
 combination with the starch. Other acid gases may, however, produce
 the same effect. A second test should, therefore, be tried. Soak red
 litmus paper with a very dilute solution of potassic iodide, and
 expose as before. Potassic oxide is produced if ozone is present, and
 this turns the litmus blue.

=Aqueous Vapour= is always present in air, though the amount varies
greatly. It is invisible in the ordinary condition, but by condensation
becomes cloud or fog, rain, snow, or hail. The quantity of moisture
present varies with the temperature of the air; the higher the
temperature, the more water can be vaporised, without the point of
saturation being reached. An increase of 27° Fahr. doubles the capacity
of air for moisture. The amount of moisture that would saturate air at
50° Fahr. only gives 71 per cent. of the saturation amount at 60° Fahr.
The amount of moisture is estimated by the _hygrometer_ (page 240).

Air saturated with moisture at 32° Fahr., holds vapour equal to 1∕160
of its weight; at 59° it holds 1∕80, at 86° 1∕40, at 113° 1∕20, and at
140° 1∕10.

=Ammonia= in normal air does not exceed one part in a million of
air; but it is always present—either as free ammonia or as sulphate,
chloride, carbonate, or sulphide of ammonia. From this source, plants
derive some of the nitrogen they require as food; some also from the
free nitrogen, which is fixed by certain microbes, growing in the
nodules connected with the roots of peas, lentils, and other plants
(page 274).

Traces of nitrous and nitric acid are also present in the air, produced
by the direct combination of nitrogen and oxygen occurring as the
result of the electric spark during lightning.

=Carbonic Acid= or carbon dioxide is always present in air, in the
proportion of 3·36 to 4 parts in 10,000; but in impure air may be
present in much larger amount. It is a heavy gas, incapable of
supporting combustion, and therefore of supporting animal life. Being
a heavy gas, it tends to accumulate where it is produced, as about
lime-kilns by the heating of chalk. Thus CaCO₃ (chalk) (heated) = CaO
(lime) + CO₂ (carbonic acid). Tramps have occasionally died of carbonic
acid poisoning through sleeping near lime-kilns.

It is produced by the oxidation of carbonaceous matters, hence in all
ordinary combustion, in many cases of putrefaction and fermentation,
and in the respiratory processes of all animals.

Plants diminish the amount of carbonic acid in the atmosphere. Two
processes occur in most plants: a process of respiration, as in
animals; and a process of assimilation, by which the leaves and all
other green parts of a plant under the influence of sunlight decompose
the carbonic acid of the atmosphere, fixing its carbon and liberating
its oxygen. Plants such as fungi, which are destitute of green
colouring matter, cannot decompose carbonic acid; nor can any plants
during the night. During the day green plants are air purifiers; during
the night all plants vitiate the air to a slight extent.

=The Air in Relation to Respiration.=—The oxygen of air is absolutely
essential for the continuance of life. In every organised animal,
_lungs_ or analogous organs are provided, in order to supply the
necessary oxygen to the system, and to remove the impure air from it.

The act of breathing occurs in man about seventeen times per minute.
While the inspired air is in contact with the interior of the lungs, it
undergoes important alterations. It comes into contact with the five or
six millions air-vesicles which form the minute dilated terminations
of the windpipe, and have an aggregate area of ten to twenty square
feet. Each of the air-vesicles has extremely thin walls; and outside
these delicate walls lie capillary blood-vessels, full of impure
blood. An active interchange now occurs between the air and the gases
dissolved in the blood. Oxygen passes through the intervening membrane
into the blood, while carbonic acid and other impurities of the blood
pass into the air-vesicle. The consequence of this is that the impure
dark-coloured blood becomes bright scarlet and pure. This purification
is not confined to any one portion of the blood; for the heart
contracting 60 or 70 times per minute, pours successive portions of
blood into the capillaries surrounding the air-vesicles; while at the
same time, pure air is brought into the air-vesicles seventeen times
per minute, and so the interchange is constantly kept up.

In view of the incessant character of respiration and circulation,
it is clear that all the blood will be purified if the external air
is pure; and that if there is any detrimental matter in the air, it
probably will come into contact with the blood in the lungs.

The amount of air taken in with each inspiration is about thirty cubic
inches. This is called the _tidal air_, as it is constantly ebbing and
flowing from and to the lungs. By means of a very forced inspiration,
about 100 cubic inches of additional air can be inspired; and similarly
after an ordinary inspiration, one can expire forcibly an additional
100 cubic inches, though there will still be left in the lungs another
100 cubic inches of air. Thus:—

  _Tidal air_                            30 cub. in.

  _Complemental air_                    100  „

  _Supplemental air_                    100  „

  _Residual air_                        100  „
        _Total capacity of lungs_       330  „

Corresponding to the respiratory changes in the lungs, there are
changes in the tissues throughout the body. The pure and oxygenated
blood leaving the lungs, is carried to all parts of the system.
Oxidation and allied processes are actively carried on, the result of
which is the formation of urea, carbonic acid, and smaller quantities
of other effete matters. These are then carried by the blood to the
excretory organs, urea being chiefly eliminated by the kidneys, and
carbonic acid by the lungs.

=Examination of Expired Air= shows that—1. It is _heated_; in its
passage through the nose and deeper respiratory passages it has
acquired a temperature approaching that of the blood.

2. Its _moisture_ is increased. By the skin and lungs from 25 to 40
ounces of water pass off in the twenty-four hours; the relative amount
varies somewhat.

3. It contains 4 to 5 per cent. less oxygen, and _4 per cent. more
carbonic acid_ than inspired air. The carbonic acid, instead of being 4
parts in 10,000 of air, becomes over 400 in 10,000, while the oxygen is
diminished in a somewhat larger proportion. Thus:—

                        OXYGEN. NITROGEN. CARBONIC ACID.

  Inspired air contains  20·81    79·15       ·04

  Expired   „      „     16·033   79·557     4·38

The _amount_ of carbonic acid expired varies under different
circumstances. It is increased by active work, by an increase of food,
by a diminution of the external temperature; it is greater when the
surrounding air is pure, and when it is moist; and it varies with the
season, being greatest in spring, and least in autumn.

Children require more oxygen, and expire more carbonic acid than
adults, weight for weight. A child six or seven years old requires
nearly as much oxygen as one twice that age. Boys usually require more
air than girls, as they are more active and exhale a larger amount of
carbonic acid and other impurities.

The average amount of carbonic acid eliminated by a healthy adult is
at least 0·6 cubic foot per hour, or 14·4 cubic feet per day. This
reckoned as carbon is equivalent to 160 grains per hour, or half a
pound of carbon in the twenty-four hours. Liebig gives the amount of
carbonic acid expired as 0·79 cubic foot per hour, or 19 cubic feet per

4. It contains _organic impurities_. These are chiefly gaseous, solid
particles only being expired during coughing, or possibly during
conversation. The danger from the “breath” of patients in infectious
diseases is really associated rather with the dried discharges on
handkerchiefs, etc., than from the “breath” itself; unless droplets
of saliva discharged during speaking, or mucus during coughing, are
directly inhaled.



Pure air being essential to life and health, it is important to
ascertain the character and origin of the impurities of air.
Innumerable substance—in the condition of gases, vapours, or solid
particles—constantly pass into it, and deteriorate its quality. To
counteract this, certain purifying agencies are at work, the mechanism
of which will be considered hereafter.

Impurities are much commoner and more abundant in the air of
enclosed spaces than in the external air, as the natural processes
of purification cannot be brought to bear so efficiently in the
former case. In sick rooms, hospitals, etc., impurities arise, which
are not present where only healthy people are collected. The most
important impurities are derived from the respiration of animals,
and the combustion of gases, candles, or lamps in rooms, from sewage
emanations, from various occupations, and the air of marshes, mines,
church-yards, etc. These may be classed under two heads—_solid_
and _gaseous_; the solid being simply suspended in the air in a
finely divided condition, or floated about in a coarser condition
by currents of air. They are revealed in an atmosphere in which one
did not previously suspect their existence, by the passage of a beam
of sunlight. Light itself is invisible, but its course is rendered
visible by the particles from which its rays are reflected. Tyndall
demonstrated the presence of minute particulate matter in the air of
all ordinary situations, and showed that a large proportion of this
matter consists of germs (microbes). In his experiments with vapours
in closed tubes, floating matter was always revealed by a concentrated
beam of light, even though the air entering the tube had been first
drawn through sulphuric acid and through a strong solution of caustic
potash. If this air was then passed through a red-hot platinum tube and
across folds of red-hot platinum gauze, it became _optically empty_;
the floating matter had been burnt, and disappeared. It was therefore
organic. In subsequent experiments, he took organic solutions, as of
meat, turnip, and the like, and rendered them sterile by repeated
boiling. They remained sterile when kept in air-tight vessels or
in vessels covered with a thick layer of cotton-wool, which would
efficiently filter any entering air; but when exposed to the air,
they invariably became turbid, owing to an enormous multiplication of
germs. Clearly, therefore, air contains organic, matter, and much of
this organic matter consists of living germs. Most of these germs are
comparatively harmless under ordinary conditions. They are, however,
the causes of fermentation, putrefaction, and all the processes of
decomposition which occur in organic substances. The importance of the
exclusion of the dust of air has received an important application
in _Lister’s antiseptic_ and in the _aseptic_ system of treatment
of wounds. Formerly accidents and operations were frequently fatal;
now vast numbers of lives are saved by improved surgical methods.
The original _antiseptic_ method acted on the supposition that some
germicidal application to the wounds was necessary; now it is realized
that if, during the operation, germs are not allowed to remain in the
wound, all that is afterwards necessary to insure rapid recovery is
that they shall be prevented from entering the wound from the external
air during its process of recovery. By the adoption of such means,
large wounds can be made to heal, without the formation of a drop of
“pus” or “matter.” (See also page 110.)

=Suspended Matters= are _mineral_ or _organic_, the two being commonly
associated together. The _mineral matters_ consist largely of fine
particles of common salt, silica, clay, iron rust, dried mud, chalk,
coal, soot, and similar substances. Not uncommonly the mineral
particles are coated by, or mixed with, organic matter, the comparative
lightness of the organic matter enabling the mineral matter to float
about more easily. The objection to dust is thus intensified, for
not only is it irritating to the respiratory passages and generally
disagreeable, but it carries with it putrescent and possibly morbific
particles. The prevention of infectious diseases resolves itself
largely into means for preventing the inhalation of dust.

=Organic Suspended Matters= in the =open air= are, most commonly,
minute fragments of wood and straw, dried horse litter, fragments of
insects, the spores and pollen of plants, and microscopic plants and
animals. In addition, there is the putrescent organic matter resulting
from respiration and other organic functions.

=Indoors=, the air commonly contains, in addition, fragments of cotton,
linen, silk, or other fibres, fragments of vegetables, starch cells,
soot, charred wood, splinters from floors, etc.

=In Sick Rooms=, products of the morbid conditions may be evolved;
thus, pus-cells, particles from the expectoration, blood cells, fat
particles, epithelium, or the special germs or microbes to which
infectious diseases are due. These are disturbed by the movements
of persons, causing the dust to rise; and thus the infection of
consumption, and of the acute infectious diseases, is frequently spread.

Flies and other winged insects are important auxiliaries in the
diffusion of disease-carrying particles. Receiving some morbid
secretions on their limbs, or other parts of their bodies, they have
occasionally been the means of spreading erysipelas in hospitals, and
glanders in veterinary stables. The specific contagia of cholera,
enteric fever, and summer diarrhœa are occasionally conveyed to food by
flies which have previously alighted on latrines or privies or other
places where the stools of such patients have been deposited (page
281). The excreta of flies, which are not uncommonly deposited on
food, or on articles of furniture, have occasionally being found to
contain the minute ova of intestinal worms.

=Effects of Suspended Matters.=—The inhalation of dust is followed by
deleterious effects. We may divide the solid substances inhaled as dust
into three kinds:—dead substances, living substances, and the contagia
(microbes or germs) of various diseases.

1. =Dead Substances= inhaled for a prolonged period in various
occupations are a common cause of premature death. The _potter_ draws
into his lungs a fine silicious dust, which irritates his lungs, and
finally produces a fatal disease, known as =potter’s asthma=.

=Mill-stone Cutters= and =Stone Masons= inhale the fine particles of
stone given off from the material which is being chiselled. These
produce serious disease of the lungs.

=Pearl Cutters= inhale fine particles of pearl-dust, and as they
generally work in close rooms, and the dust is light and tasteless,
serious disease of the lungs results.

=Sand-paper Makers= inhale minute portions of glass and sand; and
=needle and knife grinders= are exposed to similar dangers, and at one
time the mortality among them was frightful. It has greatly diminished
since the introduction of wet grinding, the use of steam fans, and
wearing of respirators.

=Hemp and Flax Dressers= inhale a dust which is peculiarly irritating.
=Workers in rags and in wool= suffer in like manner from dust. The
dust from fleeces of wool, and especially from the alpaca fleece, has
produced in many cases (in the neighbourhood of Bradford and elsewhere)
an acute disease (anthrax) proving fatal in a few days. The spores
of this disease are very persistent of life (page 274), and remain
active for mischief for months after the death of the animal which had
suffered from it. The fleece can be disinfected by steam; and the use
of fans for diverting the dust created during “sorting” minimises the
danger from it.

The =miller= commonly suffers from a form of asthma, not so severe
as potter’s asthma, as the particles in this case are not equally
irritating. The =hairdresser= is liable to inhale the short fragments
of hair cut by the scissors, and the mortality of this class of workers
is high. =Miners= in coal have a surprisingly low mortality, when
accidents are excluded from the calculation; except in South Wales,
where it is slightly higher than for all males in the same district.
Coal dust is relatively free from sharp angles, and is therefore not
so irritating to the lungs as metallic dust. Consumption is relatively
rare among miners.

=The Fur-dyer= is very prone to suffer from the dust of the dyed furs,
great irritation and disease resulting in many cases.

=Artificial Flower-makers=, and those engaged in colouring arsenical
wall-papers, suffer from the inhalation of arsenical vapours, as well
as from the irritating effects of its absorption by the skin. These are
now seldom seen, owing to the almost complete abandonment of the use of
arsenic for wall-pigments.

=Cigar-makers= are liable to have their lungs irritated by inhalation
of the dust of the tobacco-leaf; and may suffer from tobacco-poisoning.

=Workers in Lead= are very liable to be poisoned by the metal, _e.g._,
house painters, potters engaged in the glazing process, in which the
ware is dipped into a solution containing lead, manufacturers of white
lead, and others. The lead is partly absorbed by the skin; in some
cases it is inhaled as dust; and more often it is swallowed, when the
workman eats his meals with unwashed hands. Of the symptoms “painter’s
colic” and “drop-wrist” are the two most important, though, in some
cases, lead shews its effects more insidiously, leading to gout and
chronic renal disease. It is now compulsory on employers to provide in
the workshop, complete washing arrangements for the use of workers in
lead. Every doctor called to attend a case of lead or phosphorus or
arsenic poisoning or anthrax, which has been acquired in an industrial
occupation, must notify the same to H.M. Inspector of Factories. This
implies inspection of the factory or workshop and the subsequent
adoption of further measures of precaution.

=Brass-founders= occasionally inhale the fumes of oxide of zinc; and
diarrhœa, cramp, waterbrash, and other troubles are the result. Those
engaged in the manufacture of =bichromate of potass=, are liable
to partial destruction of the mucous membrane of the nose, and to
irritation of the skin, with the formation, in some cases, of small

=Workers with Phosphorus=, as those engaged in the making of phosphorus
matches, not uncommonly suffer from a gradual necrosis (death) of the
jaw-bone. Those having carious teeth are especially attacked by this
disease, which is due to the fumes of oxide of phosphorus, attacking
the jaw. Improved ventilation of workshops, careful attention to the
teeth, and other measures, have greatly diminished this disease; and
it has disappeared where safety matches made from red non-volatile
phosphorus, have replaced matches made from the yellow variety.

=Chimney Sweeps= occasionally suffer from irritative skin diseases, as
well as bronchitis. In some cases the chronic irritation of the soot
has produced cancer of the skin.

 The effect of dust on workers can be seen in the mortality returns:
 Among men aged 25 to 65 years in 1881-90, the comparative mortality
 figure in England and Wales was as follows, all males throughout the
 country being taken as a standard and given as 1,000:—


       All males                      1000

  Clergyman    533           Coal miner (Derby and Notts.)    727
  Gardener     553           Carpenter                        783
  Farmer       563           Bricklayer, mason              1,001
  Teacher      604           Coal miner (Lanc.)             1,069
                             Tool and scissors maker        1,412
                             Potter                         1,706
                             File-maker                     1,810

=Remedial Measures.=—Means have been taken to diminish the prevalence
of the above dust diseases, in several cases with remarkable success.
In the case of steel-grinding, for instance, the mortality is greatest
with dry grinding, and least with =wet grinding=. Wet processes have
been applied to others of the industries named, with a like success.
Where the dust cannot be avoided, the use of =steam or electric fans=,
to deflect the dust away from the workman, has been found successful;
and in many cases, =free ventilation= of the workshops has greatly
diminished the mortality. Where none of the above measures suffice, the
use of =respirators= ought to be insisted on. Breathing through the
nostrils ought to be carefully maintained, as thus the dust is to a
large extent stopped before reaching the lungs.

The dangers of lead poisoning may be avoided by absolute =cleanliness=,
the hands being always washed before taking meals, and the nail-brush
used to secure complete cleanliness beneath the nails.

2. =Living Substances.=—The pollen of plants in some persons produces
a distressing form of disease, called =hay-asthma=, which is apt to
recur each year, and is sometimes only curable by living in a town or
removing to the sea-coast. The amount of pollen floating about in the
atmosphere is considerable; 95 per cent. of it is grass-pollen, and
this form and the pollen from pine-trees appear to be the most powerful
in inducing hay-asthma. According to some authorities, hay-asthma is
rather due to the minute particles constituting the scent of various
flowers, than to the pollen; but that is probably not the usual mode of
origin of the disease, though it may be in some cases. In some cases,
true asthma results from smelling particular plants. Here as in the
case of hay-asthma a peculiar idiosyncrasy is involved, only a very
small proportion of those exposed to the minute particles suffering
from asthma.

The spores of many fungi and of other living organisms are constantly
being floated about in the air, until they find a suitable resting
place, when they settle and proceed to grow and multiply. The souring
of milk, the fermentation of a saccharine solution, the moulding of
bread, the presence of mildew, the blighting of corn, and numerous
other phenomena are due to the growth of organisms carried by the
atmosphere from one part to another.

3. =The Contagia= (microbes or germs) of the acute infectious diseases
are minute living organisms, known as bacteria. Hence these diseases
may be carried about by currents of air, some much more easily than
others. Some of the contagia have a persistent vitality. Thus the
contagia of scarlet fever, diphtheria, or small-pox may infect a room
for months, causing the disease in question, when infected articles in
the room are disturbed. The contagia of typhus fever and of measles,
on the other hand, are short-lived, and do not usually resist free
ventilation and exposure to sunlight.

Besides the contagia of the acute fevers, _septic organisms_ may be
carried by the atmosphere. Formerly, blood-poisoning from operation
and other wounds was common; but Lister, by insisting on absolute
cleanliness of wounds, and only allowing air to have access to the
wound which had been filtered through layers of gauze and deprived of
its septic germs, has secured that wounds can now be kept perfectly
“sweet,” the suppuration in them reduced to a minimum, and the danger
of blood-poisoning almost annihilated (page 106). It had often been
noticed that recovery from even very severe injuries was common, if
only the skin remained unbroken; while the same injuries, with the
addition of a rupture of the skin, and consequent access of air, were
rapidly fatal. But to Lister is due the great honour of proving that
it was not the air which produced the mischief, but the germs it
contained, and that filtered air might be admitted with impunity.

_Erysipelas_ and _hospital gangrene_ have occasionally been carried
about in hospital wards by dirty sponges and dressings; and if the
ventilation is not perfect, particles of epithelium and pus from
diseased persons may be carried to other patients at a distance. Some
forms of _purulent disease of the eyes_ are transferable from patient
to patient, and in children some forms of _eczema_ are also contagious.



Gaseous impurities of the air are very commonly associated with
suspended matters, and it is often difficult to separate the effects of
the two.

Different gases are also often associated, and so produce modified
results. It will be convenient to consider, first of all, certain
well-marked gaseous impurities, and then others in which there is a
mixture of several gases, or of these with suspended solid particles.

Under the first head the most important impurity is—

(1) =Carbonic Acid.=—This is reckoned an impurity if amounting to more
than 5 parts in 10,000 of air. Owing to the large amount produced in
the respiration of animals, in the combustion of fires, gas, lamps,
etc., and in other natural processes, it would be much greater in
populous parts, were it not for the rapid diffusion occurring in the
air, and the purifying action of plants. The following analyses (Angus
Smith) illustrate the facts that in towns the amount rises, and is
greatest in the most populous parts, while during fogs it is greatly

  │                                          │VOLUMES OF CARBONIC ACID │
  │                                          │IN 10,000 VOLUMES OF AIR.│
  │                                          └─┬───────────────────────┤
  │_On the mountains and moors of Scotland     │                       │
  │    ──mean of 57 analyses_                  │       3·36            │
  │_In the streets of Glasgow                  │                       │
  │    ──mean of 42 analyses_                  │       5·02            │
  │_London, N., N.E., and N.W. postal districts│                       │
  │    ──mean of 30 analyses_                  │       4·384           │
  │_London, E. and E.C.──mean of 12 analyses_  │       4·745           │
  │_Manchester streets, ordinary weather_      │       4·03            │
  │_During fogs in Manchester_                 │       6·79            │

  The effects of carbonic acid gas alone must be carefully
  distinguished from those of the same gas _plus_ the organic impurities
  from respiration, with which it is commonly associated. Dr.
  Angus Smith found that air containing 3 per cent. of carbonic
  acid produced difficulty of breathing, but he was able to breathe
  comfortably an atmosphere containing 0·2 per cent. carbonic acid.
  Other observers have found they could breathe without discomfort
  air containing 1 per cent. carbonic acid. When the carbonic acid
  is derived from respiration, headache and giddiness are produced
  in many persons when the carbonic acid amounts to 0·15 per cent.
  A fatal result has occasionally occurred from the inhalation of the
  carbonic acid at the bottom of brewing vats, or about lime-kilns.
  The gaseous impurity at the bottom of wells is more commonly
  nitrogen than carbonic acid (page 102).

  The presence of an excess of carbonic acid diminishes the
  elimination of carbonic acid from the lungs, nutrition and muscular
  energy being consequently impaired. This is seen in workshops
  where the air is confined and gaslight is commonly employed;
  though the air here also contains carbonic oxide, sulphurous acid,
  and organic impurities, and these probably have a large share in
  producing the evil results.

  (2) =Carbonic Oxide= in the proportion of more than 1 per
  cent. is rapidly fatal, and has poisoned when under 1∕2 per cent.
  Poisoning by its means occurs where charcoal stoves are used, and
  especially when the charcoal is burnt in rooms with no chimney
  flue. This is an occasional mode of suicide on the continent.
  Carbonic oxide is a much more deadly poison than the dioxide
  (carbonic acid); it forms a stable compound with the hæmoglobin
  of the red blood-corpuscles, displacing oxygen from them, and is
  got rid of with great difficulty. Lace-frame makers place a coke
  stove under their work, and thus inhale the invisible gas. Headache,
  giddiness, irregular action of the heart, and depression of
  the general health result. Carbonic oxide is the most poisonous
  constituent of coal-gas, and is present in much larger quantity in
  carburetted water-gas with which coal-gas is now commonly mixed,
  than in pure coal-gas (page 115).

  (3) The inhalation of =Sulphuretted Hydrogen= produces
  headache, nausea, and diarrhœa; but in manufactures involving
  the inhalation of a small proportion of this gas the symptoms are
  much slighter.

  (4) =Sulphurous Acid= is always present in small quantities
  in the air of towns, derived from the combustion of coal and
  coal-gas. Straw-bleachers and the bleachers in cotton and worsted
  manufactories, often suffer from severe cough and bronchitis due
  to inhaling its irritating vapours.

  (5) =Carbon Disulphide= when vaporised and inhaled produces
  headache, general muscular pains, and nervous depression. It is
  used in the manufacture of waterproof coats, toy balloons, etc.

  (6) =Ammonia= produces irritation of the eyes and bronchial
  irritation. Hat-makers commonly suffer from its effects, being
  generally pale and feeble. It is difficult to say how much is due
  to the ammonia, and how much to the high temperature at which
  they work.

  (7) =Acid Fumes= are very irritating to the lungs, and in the
  case of alkali manufactures, they destroy all vegetation for
  considerable distances. _Hydrochloric acid_ produces great irritation,
  and chlorine even more so. The fur-dyer is not only subject to
  the dangers of dust, but also of the fumes of _nitric acid_, used to
  remove fat and give certain shades of colour to the fur.

  (8) =Other Vapours= evolved in various processes produce
  special symptoms. House-painters suffer from the inhalation of
  _turpentine vapour_, headache and loss of appetite commonly resulting.
  The symptoms from the commonly coexistent lead-poisoning are
  distinct. Brush-makers have a persistent cough, due to the
  inhalation of _resinous fumes_, evolved in making brushes.

  _Workers in paraffin_ are liable to an irritative disease of the
  hair-follicles of the body, followed by the formation of scars,
  almost like small-pox marks.

  _Workers in quicksilver_, as those engaged in making mirrors or
  thermometers, are prone to suffer from mercurial poisoning. The
  gums become spongy, and there is profuse salivation, also generally
  alimentary disturbance; and in some cases nervous affections,
  resulting in persistent muscular tremblings, etc.

  Under the second head—cases of inhalation of mixed gaseous
  and particulate contamination—we must consider

  (1) =The Effects of Air Rendered Impure by Respiration.=—It
  has been already stated that an amount of carbonic acid which
  could easily be borne alone, is intolerable when other products of
  respiration are mixed with it. These are chiefly organic gases and
  solids, which (unless removed quickly) render the atmosphere close
  and “stuffy”—an effect which is readily perceptible by the sense
  of smell of those entering an occupied room immediately from
  the outer air. When such a room is inhabited for a few hours,
  headache, langour, drowsiness, and yawning (which is really a cry
  for purer air) result. The soporific effects so commonly produced
  in churches, etc., are commonly due to the vitiated atmosphere,
  rather than as is supposed to the soothing effects of the sermon.

  When the exposure to foul air is _more chronic_, and occurs day
  after day, there results a general lowering of strength and vigour—both
  bodily and mental—even where no actual disease is set up.
  Oxidation processes are retarded; the consequence is an anæmic
  sallow complexion, which compares badly with the ruddy
  complexion of those spending a great part of the day out of doors.

  The prolonged breathing of air, foul from the products of
  respiration, is perhaps more common in workshops and schools than
  in private houses; but in both, a faint smell is commonly perceptible
  on entering from the open air, indicating imperfect ventilation and
  accumulation of organic putrescible matter. The preceding remarks
  are left as in the last edition. It must be noted, however, that
  recent research attaches more importance to the particulate matter
  (dust) in the atmosphere than to the amount of gaseous impurity,
  though the latter remains a convenient index of impurity.
  Experiments made by Drs. Haldane and L. Smith on themselves
  negative the older conclusion that a special organic poison exists in
  expired air. They were able without any appreciable effect on
  themselves to breathe air which was vitiated to such an extent as to
  completely prevent a match from burning; and they conclude that
  excess of carbonic acid and deficiency of oxygen are the sole cause
  of danger from breathing air highly vitiated by respiration. This
  conclusion may be accepted under the conditions of these
  experiments. Under ordinary conditions, however, the evil effects
  produced by breathing the air of crowded rooms, are due not only
  to the excess of carbonic acid and deficiency of oxygen, but also to
  the dust which is usually associated with them. This dust, which
  may be derived from handkerchiefs of patients suffering from
  influenza, consumption, sore throat, &c., or from other sources, is
  apt to be inhaled by the persons occupying such rooms.

  The =tendency to catarrhs= is greatly increased by living in a
  vitiated atmosphere. In the causation of “colds” two elements are
  concerned, the infective agent, and the condition of the patients.
  “Colds” are caused primarily by infection from previous patients.
  The nasal discharge of a “cold in the head” contains the contagium.
  This is dried on handkerchiefs, and is subsequently scattered as
  dust, and thus conveyed to others. Ordinarily there is considerable
  resisting power against such catarrhs. When, however, the general
  vitality or the local vitality of the mucous membrane of the nose,
  throat, and lungs is impaired by the breathing of impure air or by
  sitting in wet clothes after exposure to wet and cold, a catarrh is

  The close connection of =phthisis= (consumption) with overcrowding
  and the breathing of a vitiated atmosphere will be
  discussed hereafter (page 313). The polluted air acts in producing
  consumption by depressing vital functions, and diminishing the
  powers of resistance against the actual contagium of the disease,
  which is inhaled as dust, produced by the drying of the expectoration
  of consumptive patients.

  The germs of infectious diseases are propagated very rapidly in
  an impure atmosphere; and typhus fever occurs almost solely in
  conditions of overcrowding.

  In the cattle-plague of 1866, it was found that nearly all the
  cows died when crowded together in unventilated sheds, while only
  a third died when there was free ventilation.

  The effects of air containing the products of respiration in a
  _concentrated condition_, and of a deficient supply of air, have been
  shown only too well in the oft-quoted case of the Black Hole
  of Calcutta. In this case, 146 persons were confined in a space
  eighteen feet every way, with two small windows on one side.
  Next morning 123 were found dead, and the remaining 23 were
  very ill.

  In the experience of this country, the highest death-rates are in
  the most densely populated districts. The death-rate from phthisis,
  childbirth, and typhus fever for instance, is far higher in cities than
  in country-places. The fact may be explained in various ways.
  Density of population commonly implies insufficient or unwholesome
  food, unhealthy work, and poverty; but especially impurity of the
  air, uncleanliness, and imperfect removal of excreta. Of these
  factors, the vitiated air is probably the most powerful for evil.
  Children suffer more than adults from close aggregation of
  population, largely owing to the greater ease with which infectious
  diseases spread in towns.

  (2) =Coal-gas= is obtained by the destructive distillation of coal,
  free from access of air. The average composition of London coal-gas
  is hydrogen 50 to 53, saturated hydrocarbons 33 to 66,
  unsaturated hydrocarbons 3·5 to 3·6, carbonic oxide 5·7 to 7·1,
  carbonic acid 0 to 0·6, nitrogen 2·5 to 4·1, and oxygen 0·2 to 0·3 per
  cent. Of these the illuminants are olefiant gas (C₂H₄) and the
  higher hydrocarbons. Sulphuretted hydrogen and other sulphur
  compounds are present in small quantities, averaging 12 grains of
  sulphur per 100 cubic feet of London gas.

  The inhalation of coal-gas, even in small quantities, is liable to
  produce headache, and may lead to chronic poisoning if allowed to
  continue. Where the escape of gas is more extensive, as when a
  tap is left turned on accidentally during the night, two dangers may
  arise. If a light is struck in the room an explosion occurs; or
  persons may be poisoned in their sleep by inhalation of the gas.
  The most poisonous gas in coal-gas is the carbonic oxide. The
  _chief product of the combustion_ of coal-gas is carbonic acid. Some
  sulphurous acid is also produced, which is irritating to breathe,
  and injurious to bookbindings, picture-frames, etc. If the flame is
  imperfect, as when the pressure of gas is too great, some carbonic
  oxide may also escape.

  In recent years =Carburetted water-gas= has been largely
  mixed with coal-gas in certain districts. This is made by passing
  steam over heated coke. Thus

   C      +     H₂O    =    CO    +        H₂
  (coke)       (steam)  (carbonic oxide) (hydrogen)

The product is water-gas which burns with a non-luminous flame and
has no smell. For illuminating purposes it is enriched with vaporised
paraffin oil, which gives it a high illuminating power, and a smell
rather like that of coal-gas. In some towns as much as 60 per cent.
of this carburetted water-gas is mixed with 40 per cent. of coal-gas.
Now as the former contains about 30 per cent. of carbonic oxide, and
the latter only 7 per cent., a mixture of equal parts of the two gases
would contain 18·5 per cent. of carbonic oxide, and would therefore
be much more dangerous than coal-gas. This has been found to be so in
actual experience of escapes of gas.

In speaking of these products of different illuminants, it is necessary
to adopt a =standard of light=. In this country the standard has
hitherto been a light known as “one-candle power” which is given by a
sperm candle burning 120 grains per hour, or in V. Harcourt’s standard
flame by a mixture of air and pentane (C₅H₁₂). A good fish-tail or
bat’s wing burner for coal-gas gives an illuminating power equal to 16
candles, and burns from 4 to 5 cubic feet of gas per hour. Most flat
flame burners known as 4 or 5, and supposed to burn that number of
cubic feet of gas per hour, really consume nearly double this amount
of gas. In the following table the amount of various products produced
and of vitiation of air caused by various forms of illuminants is
compared, when an illumination equal to 16 candles is produced in each

  │                    │           │CARBONIC │         │         │AMOUNT OF│
  │                    │  AMOUNT   │  ACID   │MOISTURE │ OXYGEN  │VITIATION│
  │                    │  BURNT.   │PRODUCED.│PRODUCED.│ REMOVED.│PRODUCED[a]│
  │_Sperm candles_     │1740 grains│6·6 c.ft.│ 6·6 c.ft│9·6 c.ft.│   11    │
  │_Paraffin oil_      │992   „    │4·5   „  │ 3·5  „  │ 6·2   „ │    7    │
  │_Coal gas burned in │           │         │         │         │         │
  │  Argand burner     │4·8 c. ft. │2·5   „  │ 6·4  „  │ 5·8   „ │    4    │
  │  Flat-flame burner_│5·5   „    │3·5   „  │ 7·4  „  │ 6·5   „ │    6    │
  [a] Stated in terms of the number of adults who would cause an equal

Thus as an adult expires 0·6 cubic feet of carbonic acid per hour, it
follows that the amount of carbonic acid produced in one hour by the
various illuminants named in the above table, burning so as to give
a light equal to 16 standard candles, varies from 4 to 11 times the
amount produced by the adult. Candle and oils possess the advantage
over coal-gas that no sulphurous acid is produced in combustion. If the
pressure in the mains is excessive, some gas may escape through the
burner unburnt or carbonic oxide may escape.

In England the flashing-point of mineral oils has been fixed at 73°
Fahr. The material of which the reservoirs of lamps are composed should
not be glass or other breakable material, and the wick should be
contained in a small wick chamber extending nearly to the bottom of the
reservoir. Only a tight fitting wick must be used.

The best illuminant for domestic purposes is incandescent electricity,
in which no products of combustion are formed, and only a comparative
small amount of heat is produced. Electrical illumination possesses
the further advantages that there is no blackening of ceilings and no
damaging of other decorations as in illumination by gas.

(3) =Air Rendered Impure by Exhalations from the Sick.= In addition
to the ordinary impurities of occupied rooms, special impurities are
produced, varying with the character of the disease. They may include
infectious particles from the sick. In wards for consumptives and for
diphtheria, dust in the room has been found to contain the special
microbes of these diseases. Making beds, sweeping floors, &c. may help
to scatter infectious dust; hence the importance of adopting means
of cleansing which will not scatter dust, and of keeping sick-rooms
spotlessly clean. In many diseases _e.g._ consumption, a patient may
re-infect himself with such infectious dust, and thus diminish his own
chance of recovery (see page 311). Hospital wards can scarcely be too
freely ventilated; but even more important than ventilation is the
strictest cleanliness in every minute detail.

(4) =The Air of Sewers, Cesspools, etc.=, may contain the products
of decomposition of sewage, such as volatile fœtid organic matter,
carbo-ammoniacal substances, sulphuretted hydrogen, carbonic acid, etc.
The amount of these various products varies greatly under different
circumstances, such as dilution of the sewage, ventilation of sewers,
temperature, etc. The effluvia from cesspools are usually more
concentrated than those from sewers. It appears fairly certain that the
emanations from sewers or drains may give rise to diarrhœa and gastric
disturbances, and to certain forms of sore throat, which favour the
production of diphtheria. On the other hand, there is much evidence
showing that the danger from sewer-emanations has been exaggerated.
Carnelley and Haldane found that the air of the sewers of the Houses
of Parliament and of certain sewers of Dundee was not very impure,
containing a smaller number of bacteria than external air. There is
reason to believe that the emanations from well-ventilated sewers,
possessing a good gradient, so that the contents of the sewers are
hurried away to the outfall, are free from danger. The chief source of
possible danger would be the escape of the bacteria of such diseases
as enteric fever or diphtheria, which had been discharged into the
sewer from patients suffering from these diseases. But, in the absence
of splashing, these bacteria could not escape from a liquid medium.
Their escape could only occur when the sewer became dry, and the dust
was carried up by rapid currents of air, a very improbable occurrence
in sewers. Hence in the majority of instances sewer emanations must be
freed from the accusation of producing infectious diseases. Sewer-men
usually enjoy good health, and there is no excess of infectious
diseases among them.

The emanations from _obstructed drains or sewers_ may cause serious
mischief, similarly to that occasionally produced by the emanations
from cesspools. Under such conditions, sulphuretted hydrogen,
carburetted hydrogen, and other gases are evolved, and fatal asphyxia
has been caused by these. In other instances acute sewer-gas poisoning,
without pneumonia, has followed.

The exhalations from cesspools or privies while cleaning them out,
may produce severe disorders, which are sometimes fatal. When a drain
is newly opened or sewer gas gets into a house, a less marked form
of poisoning sometimes occurs, chiefly characterised by languor,
headache, vomiting, and diarrhœa. In some cases there may be febrile
attacks lasting a few days. Children are especially sensitive to such
conditions and quickly fall into ill health.

The direct origin of acute infectious diseases from the effluvia
from drains or cesspools has occasionally occurred. Leaky and choked
drains under a house are especially dangerous. The subsoil becomes
contaminated more and more as time goes on; foul gases are aspirated
into the house, owing to its interior being warmer than the subsoil;
and finally infectious matter may find its way into the house, or
carried by insects or vermin, through cracks in the earth.

_Diphtheria_ has been ascribed to emanations from drains and sewers.
There is reason to believe that a non-specific form of sore throat
may originate in this way; but diphtheria is generally, if not always,
spread by personal infection. _Diarrhœa_ has been occasionally ascribed
to sewer-emanations. It chiefly occurs in hot weather, and is usually
associated with a foul condition of the surface soil, and speedily
ceases after this has been scoured by copious rain.

_Enteric or typhoid fever_, has been frequently ascribed to drain and
sewer effluvia. It was formerly thought that putrefactive changes
alone, under certain conditions of temperature, etc., would produce
it, and Dr. Murchison, one of the greatest authorities on the subject,
who adopted this view, proposed for enteric fever the name “pythogenic
fever” (_i.e._ filth-produced). Isolated cases of enteric fever,
occurring where there is no system of drainage, support the same view,
as does also the fact that, with the adoption of drainage, the enteric
mortality has steadily diminished. On the other hand, numerous cases
can be quoted to show that emanations from excreta have been breathed,
and sewage-contaminated water drunk, for years, without the production
of a single case of enteric fever—until a case is accidentally
imported. The weight of evidence is clearly on the side of the view
that only emanations from the liquid or solid dejecta of previous
enteric patients will produce enteric fever, and that it is the solid
particles of the urine or fæces, either inhaled as dust or carried on
to food by flies, &c., or mixed with food by contaminated water, &c.,
which cause infection. Furthermore, modern investigation shows that
infection by dust is the exception in England; and that the enteric
infection is usually swallowed and not inhaled, being taken in infected
water or milk or other food.

(5) =Effluvia from Decomposing Organic Matter.=—(_a_) =The air of
marshes= contains an excess of carbonic acid, marsh gas, etc., in
addition to other organic matters. Malarial diseases are commonly
ascribed to the inhalation of the marsh effluvia under certain
conditions, though the recent proof of the part played by the mosquito
in spreading malaria, puts the inhalation of such effluvia in the
background as cause of this disease (page 307). Some forms of diarrhœa
and dysentery have been ascribed, with a less degree of probability,
to the same cause. In this case, as in that of emanations from other
organic sources, the impurities received by the air are both gaseous
and particulate.

(_b_) =The Air of Graveyards= contains an excess of carbonic acid. The
older intramural graveyards appear to have been a cause of illness; but
modern graveyards, kept under good regulations have never been shown to
cause illness.

(_c_) =The Effluvia from Decomposing Carcases=, especially of horses on
the battle-field, have led to outbreaks of diarrhœa and dysentery among
the soldiers.

(_d_) =The Effluvia from Manure and Similar Manufactories= do not seem
to injure the workmen as a rule, but attacks of diarrhœa have been
produced in the neighbourhood when the wind has wafted the effluvia
towards any particular part. Sore throat, and occasionally diphtheria,
have been ascribed to the inhalation of London manure taken into Essex.

(6) =The Effluvia from Certain Manufacturing Processes= seem to be
rather nuisances than actually productive of ill health. The vapours
given off by _tallow-making_ and _bone-burning_ processes are most
disagreeable, but there is little or no positive evidence of their
direct insalubrity.

The air of _brickfields_ and cement works is peculiarly disagreeable.

=The Degree of Moisture and the Temperature= of air are of great
importance in relation to health. Air which is unduly moist or dry, hot
or cold, may be injurious apart from any foreign matters it contains.

The _relative amount of moisture_ is of greater importance than its
actual amount. An atmosphere which contains aqueous vapour up to the
point of saturation is very oppressive; the normal evaporation of
insensible perspiration (and with it of the organic impurities removed
from the skin) is interfered with; and consequently the “oppressiveness
of the day” is complained of.

_An unduly hot air_ is generally productive of pallor and ill
health, though it is difficult to know how much to ascribe to the
high temperature, and how much to the commonly coexistent vitiated
atmosphere. The temperature of living-rooms ought not to be over 60° to
65° Fahr., and of bedrooms not over 60° Fahr.

The devitalising influence of extreme _cold_ is well known. Its effects
are more particularly seen in young children and the very old, who
require to be carefully tended during severe and long-continued cold
weather. Dry, cold weather, with the temperature near the freezing
point of water, and a cutting east wind prevailing, is not uncommonly
described as “bracing.” This is so far from being the case, that it
requires all the vital powers of the strong and healthy to resist its
depressing influence, and the feeble of both extremes of age succumb.



Many occupations are the source of considerable danger to the workers
engaged in them. They are chiefly injurious by the inhalation into
the lungs of some foreign agent, which produces serious local
inconveniences and irritation, and may be also absorbed into the
circulation and produce more remote effects.

The injurious agents may be classified under four heads:—

(1) Insoluble particles or dust.

(2) Soluble or partially soluble substances.

(3) Injurious gases or vapours.

(4) Effluvia from offensive trades.

It is evident that, as regards the effluvia named under (4), they might
generally be included under the three previous heads, though it is
convenient for our present purpose to keep them separate.

The occupations in which dust and soluble substances are productive of
injurious effect have already been described, pages 107 to 109.

Injurious gases and vapours have received consideration on pages 111
and 112. The special offensive trades still require attention.

=Offensive Trades.=—The legal enactments relating to offensive trades
are contained in sect. 112 of the Public Health Act, 1875, which
states, any person who, after the passing of this Act, establishes
within the district of an urban sanitary authority, without their
consent in writing, any offensive trade, that is to say, the trade of—

  Blood boiler, or
  Bone boiler, or
  Fellmonger, or
  Soap boiler, or
  Tallow melter, or
  Tripe boiler, or
  any other noxious or offensive trade, business, or manufacture,

shall be liable to a penalty not exceeding fifty pounds in respect of
the establishment thereof, and a penalty not exceeding forty shillings
for every day on which the offence is continued.

These provisions can only be enforced in rural districts with the
sanction of the Local Government Board.

The “other noxious or offensive trades,” in order to be brought within
the operation of the section, must be analogous to those which are
specially enumerated.

The most exhaustive and authoritative report on this subject is by
the late Dr. Ballard, whose report is largely quoted in the following

We may consider (1) _the extent to which the public is inconvenienced
by various effluvium nuisances_. The majority of the nuisances arise
from trade processes in which animal matters are chiefly used. Among
the most disgusting are the effluvia from gut-scraping, and the
preparation of sausage skins and catgut, the preparation of artificial
manures from “skutch” (the refuse matter of the manufacture of glue),
the manufacture of some kinds of artificial manures, and the melting
of some kinds of fat. Manufacturing businesses dealing with vegetable
substances are often offensive, but rarely give out disgusting
effluvia. The most offensive vegetable effluvia are probably those
thrown off during the heating of vegetable oils, as in the boiling of
linseed oil, the manufacture of palmitic acid from cotton oil or palm
oil, the manufacture of some kinds of varnish, the drying of fabrics
coated with such varnishes, and the burning of painted articles, such
as disused meat-tins.

Occasionally offensive effluvia arise in connection with industries
in which neither vegetable nor animal matters are used; as in the
manufacture of sulphate or chloride of ammonia, and some other
processes in which sulphuretted hydrogen is copiously evolved; and
in the making of gas and the distillation of tar. The fumes from the
manufacture of alkali and bleaching powder are acid and irritating, and
produce very injurious effects on vegetation in the neighbourhood.

The distances to which nuisances extend vary greatly according to
circumstances—as, for instance, the elevation at which the effluvia
are discharged into the air. Discharge from a high chimney may relieve
the immediate vicinity of the works at the partial expense of those
living at a greater distance. With a damp and comparatively stagnant
atmosphere, effluvia have a much greater tendency to cling about a

(2) The industrial processes in which offensive effluvia are produced
are _classified_ by Dr. Ballard as follows:—

 1. The keeping of animals.

 2. The slaughtering of animals.

 3. Other branches of industry in which animal matters or substances of
 animal origin are chiefly dealt with.

 4. Branches of industry in which vegetable matters are chiefly dealt

 5. Branches of industry in which mineral matters are chiefly dealt

 6. Branches of industry in which matters of mixed origin (animal,
 vegetable, and mineral) are dealt with.

(3) It is important to inquire _to what extent offensive trade
effluvia are injurious to the public health_. It is impossible to
bring statistics to bear on the inquiry, as other influences, apart
from occupation, can scarcely be eliminated. The term “injurious to
health” is capable of a double interpretation. It might mean either
serious damage to health, or the mere production of bodily discomfort
or other functional disturbance by the offensive effluvia, leading by
its continuance to an appreciable impairment of vigour, though not to
any actual disease.

In the latter sense offensive effluvia have a deleterious effect
on health. Such symptoms as loss of appetite, nausea, headache,
occasionally diarrhœa, and general malaise are produced by effluvia of
various kinds, but agreeing in being all offensive. “A condition of
_dis_-ease or _mal_-aise is produced.”

There is little difficulty in proving bad effects on the workmen,
though the invariable defence of manufacturers is an appeal to the
condition of health of their workmen. The workmen only remain such so
long as they are healthy, and as they become disabled they necessarily
cease to rank among workmen. The decomposition of putrefying
organic matters is unquestionably dangerous. The general doctrine
of sanitation that filth is one of the chief factors in producing
disease is certainly applicable to trade effluvia as well as to general
sanitation. It has been alleged on behalf of such effluvia as chlorine
sulphurous acid and tar vapours that they are useful disinfectants;
but modern research has shown that disinfectants, in order to be of
practical use, must be in such a concentrated condition that the air
containing them is irrespirable. Probably such septic diseases as
erysipelas are favoured by organic trade effluvia.

(4) _The means available_ to prevent or minimise the nuisances arising
from trade effluvia vary with the character of the processes. The
general principles on which treatment must be founded depend, as
Dr. Ballard points out, on a recognition of the following kinds of

Effluvia dependent—

 1. On the accumulation of filth on or about business premises, or on
 its removal in an offensive condition.

 2. On a generally filthy condition of the interior of buildings and
 premises and utensils generally.

 3. On an improper mode of disposal of offensive refuse, liquid or

 4. On insufficient or careless arrangements in reception of offensive
 materials of the trade, or in removal of offensive products.

 5. On an improper mode of storing offensive materials or products.

 6. On the escape of offensive gases or vapours given off during some
 part of the trade processes.

It is evident that under the first two headings the proper remedy is
cleanliness. Filth should be removed in impervious covered vessels,
at regular intervals. Structural arrangements should be made, which
will facilitate cleansing operations. Solid refuse should, as far as
possible, be separated from liquid refuse, as thus putrefaction is

Under the last head important remedies are applicable. In many cases
a careful selection of the materials of manufacture will form an
effective remedy. Thus much of the nuisance connected with soap or
candle works arises from the putrid condition of the fat collected
from butchers and marine store dealers, and might be obviated by more
regular and more frequent collection of the materials of manufacture.
The offensive vapours arising during processes of manufacture may be
intercepted before reaching the external air, and so treated that
they lose their obnoxious character. Various methods of interception
are adopted, according to the processes involved. Occasionally it is
necessary to have the air of the entire workshop drawn by means of
artificial ventilation in a special direction; usually the interception
of air from special chambers suffices. When thus collected, the
offensive air may be dealt with by (1) passing it through water or
some other liquid capable of absorbing the offensive materials; or (2)
passing it through some powder with which it has chemical affinity; or
(3) if its offensive materials are capable of condensation by cold,
passing them through an appropriate condensing apparatus; or (4) if the
evolved matters are organic in nature, conducting them through a fire.
(5) Occasionally it is sufficient to discharge the offensive gases into
the air from a high chimney; and this always produces a mitigation of
nuisance, as compared with discharge at a low level.

It is usually found that the adoption of one or other of these methods
is directly or indirectly profitable to the offender.

=Nuisances from the Keeping of Animals.=—The 47th section of the
Public Heath Act prohibits the _keeping of pigs_ in towns so as to
be a nuisance, and, as a general rule, it is possible to obtain a
magistrate’s order, entirely prohibiting the keeping of pigs in towns.
The excreta of the pig have a very offensive and penetrating odour, and
however carefully kept, pigs in towns form an intolerable nuisance.

Not only is there nuisance from the accumulation of manure and
dirtiness of the piggeries, but also from the storage and subsequent
preparation of food. The boiling of hog-wash is often an even greater
nuisance than the filth of the styes.

_Cow-keeping_ and _horse-keeping_ in towns are still allowed and, as
compared with pig-keeping, form a small nuisance. Mews, if kept clean
and well drained, need not be offensive, though it is objectionable for
persons to sleep over stables. The removal of manure also constitutes
a difficulty. The manure should not be allowed to accumulate in deep
wet pits, but in an iron cage-work over a cement paving at or above the
ground-level, thus allowing free drainage, and keeping the manure dry,
and reducing ammoniacal decomposition to a minimum.

Cowsheds are generally very badly ventilated, as the cowkeeper finds
that more milk is produced by the cows when the temperature of the
shed is maintained at 65° or higher; and he does not see the necessity
for providing artificial means of warmth. The grains which are used
so largely for food are stored in a wet condition, and speedily give
rise to nuisance. Cowsheds and stables should be well paved and well
drained. At least 800 cubic feet should be allowed for each cow in the

Cowsheds are regulated under the Dairies’, Cowsheds’, and Milkshops’
Order of the Local Government Board. This order provides for and
insists on the registration of cowkeepers, dairymen, and purveyors
of milk, by the local authority. It also provides that no cowshed
or dairy shall be occupied as such, unless provision is made to the
satisfaction of the local authority, for the lighting and ventilation,
including air-space, and the cleansing, drainage, and water-supply
of the same; and for the protection of the milk against infection or
contamination. With the view of preventing contamination of milk, no
person suffering from an infectious disorder, or having recently been
in contact with a person so suffering, is allowed to milk cows or take
any part in any stage of the business of a milk-seller. The milk of a
cow suffering from cattle plague, pleuro-pneumonia, or foot and mouth
disease must not be mixed with other milk, must not be sold or used
for human food, nor for food for swine or other animals, unless it has
been boiled. By the order of 1899 this regulation is made to extend to
tubercular disease of the udder.

_Slaughtering of Animals._—Nuisance may arise in slaughter-houses from
various causes:—(1) the uncleanly way in which animals are kept in the
pound or lair before being killed; (2) the insanitary condition, bad
paving, lack of lime-whiting of walls, etc., of the slaughter-house;
(3) the accumulation of hides, blood, fat, offal, dung, or garbage on
the premises; (4) the uncleanly condition of the blood-pits, or the
receptacles for garbage; (5) the flowing of blood or offal into the
drains and thence into the public sewer.

Private slaughter-houses ought to be abolished, and all animals
intended for human food slaughtered in public abattoirs under efficient
supervision. When a large number of private slaughter-houses exist in
different parts of a large town, it is impossible for the sanitary
officials to properly supervise the slaughtering, or to ensure that
diseased meat shall not enter the market. The inspector may only have
the opportunity of examining the flesh, the internal organs which more
particularly show the presence of a diseased condition having been
concealed. Such concealment and the consequent foisting of diseased
meat upon the public, can only be efficiently prevented by forbidding
the slaughtering of any animal intended for food in a private

Most local authorities have bye-laws regulating the slaughtering of
animals. These provide for a cleanly condition of the lairs, and
prevent keeping the animals longer in the lairs than is necessary for
the purpose of preparation for slaughtering. They also insist on the
provision of proper covered receptacles of iron or other non-absorbent
material for the reception of garbage, and similar receptacles for
blood; for cleansing of the floor, etc. after slaughtering; for
lime-whiting of the walls four times a year; and for other matters of

For _knackers’ yards_ similar regulations are applicable. The flesh
should not be kept until it becomes putrid before being boiled, and
the boiling of the flesh and fat should be so arranged as to avoid the
escape of offensive vapours into the external air.

In _smoking bacon_, the singeing has formed a serious nuisance.
_Fish-frying_ in small shops is often a most troublesome nuisance.
A hopper over the pan in which the frying is conducted has not been
always successful in carrying the fumes up the chimney. The frying
should preferably be done in a closed outhouse, close to a chimney with
a good up-draught.

The _fellmonger_ prepares skins for the leather-dresser, the chief
operations being taking off the wool, liming the skins, etc. The skins
deprived of wool are called “pelts.” The pelts are thrown into a pit
containing milk of lime, and thence sent direct to the leather-dresser.
Nuisance may arise from (1) the odour of the raw skins; (2) the
ammoniacal odour from the lime-painted skins hanging in the yard; (3)
the emptying and cleansing of the “poke” or tank in which the hides
are washed; (4) the foul condition of the waste lime taken from the
exhausted lime pits; (5) the odour from the dirty unpaved yards.

The _leather-dresser_ only deals with “pelts,” derived from
sheep-skins; the tanner with bullocks’-hides. The skins brought from
the fellmonger to the leather-dresser are first deprived of lime,
and then soaked in a solution of dog’s dung, called “pure,” until
they become soft. In winter this “pure” solution is warmed for use.
The odour is very abominable, both from the “pure” tub, and from the
discharge of the exhausted “pure” liquid into the drain.

At each stage of _tanning_ nuisance may arise unless great precautions
are taken, as when the hides are soaked in lime and water, when the
hair is being removed, when the loose inner skin of the hide is being
removed, and especially when the hides are soaked in pits containing
pigeons’ or other dung. Nuisance may arise again during the passage of
offensive hides through the street. Cleanliness is the great rule. If
every process is carried on with due precaution, including frequent
washing out of receptacles and the free use of disinfectants, little
complaint need arise.

The manufacturers of _glue_ and _size_ boil out the gelatine from
bits of hides and “fleshings” from leather dressers and tanners,
from damaged “pelts,” ox or calves’ feet, horns, and other similar
substances. The raw material is apt to be offensive in collection or
while accumulating on the premises. The process of boiling causes
offence by the effluvia from the steam. The residue remaining after the
process is known as “scutch,” and this, unless frequently removed, is a
most serious source of nuisance.

_Prussiate of Potass_ is manufactured by heating carbonate of potass
with refuse animal matters. In order to avoid nuisance the pot in which
the boiling is done should have a pipe to conduct away the steam, first
running horizontally and then vertically down to the back part of the

_Fat-melting_ and _Dip-candle-making_, as usually carried on, give rise
to nuisance. The fat which is melted down usually comes from butchers
and marine-store dealers in a rancid or even putrid condition, and
it may be stored on the premises for some time before it is boiled.
The vapours from the melting-vat are very offensive. They should
be carried by means of a pipe down until they discharge just under
the boiler-fire. The residue from the fat-melting process (known as
“greaves”) requires frequent removal to avoid nuisance.

_Bone-boiling_, in order to extract the fat and gelatine, is most
offensive, and most difficult to deal with. After boiling, the bones
are apt to give off offensive smells. The vapours from the closed
boiler should be condensed as far as possible in a worm condenser, and
the remainder passed through a furnace fire.

In the manufacture of _artificial manures_ nuisance is apt to arise (1)
from the reception and accumulation of the raw materials, as putrid
fish, putrid blood, scutch (the residue from the manufacture of glue),
recently boiled bones, etc.; (2) from the preparation of the raw
material for use. Thus the drying of condemned fish or meat on open
kilns is very offensive; similarly the drying of sewage sludge. (3)
From the process of mixing the materials of manufacture, irritant and
offensive vapours being evolved, as for instance in the manufacture of
manure by crushing bones, and converting into super-phosphate by the
addition of sulphuric acid. (4) From the removal of the manure from the
hot den, after it has been dried. When sulphuric acid is mixed with
coprolites or other mineral phosphates, most irritant and offensive
vapours are produced, which may be perceived in some cases at the
distance of a mile.

_Blood-boiling_ is now almost obsolete, having been replaced by
albumen-making and clot-drying. Nuisance may arise from the blood
collected from slaughter-houses being in a putrid state; and from the
effluvia evolved during the drying process.

_Gutscraping_, _gut-spinning_, and the _preparation of sausage-skins_
are very closely akin. In gut-scraping the putrid intestines are
deprived of their interior soft parts by scraping with pieces of
wood, and are then, after being cleansed, ready for sausage-skins.
In gut-spinning the prepared gut is twisted into a cord. The small
intestines of hogs and sheep are used for this purpose. The stench from
these establishments is indescribably horrible. Extreme cleanliness is
desirable. Immersion of the guts in common salt is useful; so also the
use of impervious vessels, early removal of all refuse material, etc.

Brick and ballast burning are a frequent source of complaint in the
neighbourhood of towns. _Brick burning_ is conducted either in kilns
or clamps. When bricks are burnt in closed kilns comparatively little
nuisance arises; but when they are burnt in open clamps the effluvia
are very irritating, partly owing to the fact that very commonly
house refuse, containing vegetable and animal matters, is burnt with
the bricks. Clamp burning should be absolutely prohibited in the
neighbourhood of large towns.

In _Ballast burning_ stiff clay is converted by the agency of heat
into a brick-like material, which is of use in road-making. The clay
is usually burnt in heaps, mixed with ashes and breeze from dust-bins.
The process is offensive unless carried on with precautions similar to
those for brick-burning.



There are various methods of ascertaining the quality of the air in
enclosed spaces, of which not the least useful is the information
furnished by the _sense of smell_, on entering a room from the
external air. Besides the evidence given by the senses, _chemical_ and
_microscopical_ examination of the air gives important information,
while the _thermometer_ and _hydrometer_ ascertain the temperature and
degree of moisture.

=Examination by the Senses.=—The dull grey haze hanging over a town,
when it is viewed from a distance, indicates comparative impurity of
its atmosphere, and the presence of a considerable amount of suspended
matter, including smoke.

The _smell_ of a stagnant atmosphere is a good preliminary guide to its
condition. The fact that a room has been occupied for some time without
efficient ventilation can be at once detected on entering a room from
the external air. The sense of smell is extremely delicate; it has
been estimated that the 3∕100,000,000 part of a grain of musk can be
apprehended by it. But nothing is so soon dulled as the sense of smell.
An atmosphere which did not appear to be unpleasant while remaining in
a room, is intolerable when one returns to it after a few minutes in
the open air. It is important not to confound the “closeness” perceived
by the sense of smell, with the oppression due to the high temperature
of a room. The two are easily distinguished (unless the two co-exist)
by a reference to the thermometer, which ought always to be placed in
rooms inhabited during the evening. The remedy for a close room is to
allow free entry of fresh air, and _not_ allow the fire to go down, as
is so commonly done, under the impression that the closeness is due to

De Chaumont has made many experiments, shewing how accurate is the
information given by an acute sense of smell. Carbonic acid is
destitute of odour, but as its amount is usually proportionate to that
of the organic matter producing closeness, it may be taken as an index
of the amount of impurity present in living rooms. De Chaumont found
that the limit of smell is reached when carbonic acid amounts to 6
parts in 10,000 of air, or half as much again as in the external air.
In the following extracts from his experiments, there was a close
accordance between the evidence of his sense of smell and the amount of
carbonic acid:—

  │_At_ 14·8_ per_ 10,000 { _Extremely close   │
  │                       {  and unpleasant._  │
  │ „   10·90     „         _Extremely close._ │
  │ „    9·62     „         _Very close._      │
  │ „    9·21     „         _Close._           │
  │      8·43     „         _Not very foul._   │
  │ „    8·04     „         _Close._           │
  │ „    6·58     „         _Not very close._  │
  │ „    5·68     „         _Not close._       │

He also found that humidity of the air had marked influence in
rendering the smell of organic matter perceptible, even more than a
rise of temperature. The sense of smell is doubtless aided in detecting
impurities in the air, by the _besoin de respirer_, a feeling of
oppression caused by the deficiency of interchange between the blood
and air. The state of cleanliness of the room as well as of the persons
in it influences smell; hence there may not be in particular instances
exact correspondence between excess of carbonic acid and of organic

=Chemical Examination.=—The estimation of nitrogen and oxygen in air
is usually unnecessary, as these vary but little. The oxygen is,
however, reduced in frequently re-breathed air. The ill effects of an
often-breathed atmosphere are due not only to deficiency of oxygen, but
also to the addition of carbonic acid and organic matters, rendering
difficult the interchange between oxygen and the blood.

=The Estimation of Carbonic Acid= is of great importance, as under
ordinary circumstances, its amount is a fairly exact indication of the
amount of contamination in the air.

 =Pettenkofer’s Method.=—A carefully dried glass vessel containing a
 gallon of water is filled with the air to be examined, by emptying the
 water in the room, the air of which is to be examined. Fifty cubic
 centimetres of clear freshly prepared baryta water are then added, and
 the stopper of the bottle then replaced. It is then well shaken, and
 afterwards allowed to stand for an hour. The carbonic acid combines
 with part of the baryta to form barium carbonate; and the baryta
 water remaining is consequently diminished in alkalinity. Given the
 alkalinity of the baryta water before and after the experiment, and
 the difference will give the amount of baryta which has combined with
 carbonic acid.

 The alkalinity of the baryta is estimated by a standard solution
 of oxalic acid, of such a strength that 1 c.c. is the equivalent
 of 0·5 c.c. of CO₂. The indicator used in making this test is
 phenolphthalein, which colours baryta water red, but its colour
 disappears when neutralization is reached.

 The following example is taken from “Pakes’ Laboratory Text Book of
 Hygiene,” p. 292:—

 The jar is found to contain 3,950 c.c.

 As 50 c.c. baryta water were run into the jar, the air experimented on
 = 3,950-50 = 3,900 c.c.

 On titrating 25 c.c. of the original baryta water, 22·50 c.c. standard
 acid solution were required to neutralise it.

 The baryta water in the jar required 19·35 c.c.

 22·50-19·35 = 3·15 c.c. = difference of acid used.

 But 1 c.c. acid = 0·5 c.c. CO₂ at 0° C. and 760 mm. of mercury.

 Therefore CO₂ taken up by 25 c.c. of baryta = 3·15∕2 = 1·575 c.c.

 As 50 c.c. were used the CO₂ absorbed by the baryta = 3·15 c.c. This
 was present in 3,900 c.c. of air. Therefore the CO₂ = 0·80 per cent.

 Correction may be required for variations from the normal pressure of
 760 mm. and normal temperature of 0° C., in accordance with ordinary

 =In Lunge and Zeckendorf’s Method=, the air to be examined is pumped
 through a glass bottle in which is 10 c.c. of a N/500 solution of
 Na₂CO₃ containing phenolphthalein as an indicator. The air is pumped
 by a hand pump through this solution until the phenolphthalein is
 decolourized. The number of times the ball of the pump has been
 squeezed indicates the amount of CO₂ present in accordance with a
 table prepared from separate experiments by Pettenkofer’s method.

 =Dr. Angus Smith’s plan= for the estimation of carbonic acid in air is
 similar in principle to the last calculations. It is based on the fact
 that the amount of carbonic acid in a given volume of air will not
 render turbid a given amount of lime water, unless the carbonic acid
 is in excess.

 TABLE.—_To be used when the point of observation is “No precipitate.”_
 Half an ounce of lime water containing ·0195 gramme lime.


  │  IN THE AIR   │     CUBIC      │      CUBIC      │     OUNCES      │
  │     ·03       │      571       │       584       │      20·63      │
  │     ·04       │      428       │       443       │      15·60      │
  │     ·05       │      342       │       356       │      12·58      │
  │     ·06       │      285       │       299       │      10·57      │
  │     ·07       │      245       │       259       │       9·13      │
  │     ·08       │      214       │       228       │       8·05      │
  │     ·09       │      190       │       204       │       7·21      │
  │     ·10       │      171       │       185       │       6·54      │
  │     ·11       │      156       │       170       │       6·00      │
  │     ·12       │      153       │       157       │       5·53      │
  │     ·13       │      132       │       146       │       5·15      │
  │     ·14       │      123       │       137       │       4·82      │
  │     ·15       │      114       │       128       │       4·53      │
  │     ·20       │       86       │       100       │       3·52      │
  │     ·25       │       69       │        83       │       2·92      │
  │     ·30       │       57       │        71       │       2·51      │

 The foregoing table shows how to apply this method. The first and
 second columns state the ratio of carbonic acid in a quantity of air
 which will give no turbidity or precipitate in half an ounce of lime
 water; the third column gives the corresponding size of the bottle in
 cubic centimetres; and the fourth column gives the same in ounces.
 Thus different sized bottles, each containing half an ounce of lime
 water, will indicate with a fair degree of accuracy the ratio of
 carbonic acid in the air containing them, by giving no precipitate
 when the bottle is well shaken. For instance, if a pint bottle is
 used and there is no precipitate with half an ounce of lime water, it
 indicates that the ratio of carbonic acid does not amount to ·03 per
 cent.; if an eight-ounce bottle be used, and there is no precipitate,
 it indicates that the ratio does not amount to ·08 per cent., and so
 on. The air of a room ought never to contain more than six parts of
 carbonic acid in 10,000 of air, or ·06 per cent., _i.e._ a 10½
 ounce bottle full of the air shaken up with half an ounce of clear
 lime water ought to give no precipitate.

 _Dr. Haldane_ has recently described (_Journal of Hygiene_, No.
 1, 1901) a method of estimating CO_2, which, although it appears
 complicated, is really both simple and convenient. For particulars,
 see the above _Journal_.

 =The Estimation of Organic Impurities= may be accomplished
 approximately by drawing a definite amount of air by means of an
 aspirator, through a dilute solution of permanganate of potassium of
 known strength. The result is stated by giving the number of cubic
 feet of air required to decolourise .001 gramme of the permanganate in
 solution. Sulphuretted hydrogen, sulphurous acid, and other substances
 in air likewise decolourise the permanganate; these ought to be
 separately tested for, and allowance made.

 =The Estimation of Ammonia=, whether free or derived from albuminoid
 impurities, is a matter requiring very delicate processes. It is
 accomplished in the same way as the estimation of ammonia in water,
 the air being drawn through perfectly pure distilled water, and then
 the analysis proceeded with as a water analysis. The mere presence
 of free ammonia may be determined by exposing to the air strips of
 filtering paper dipped in Nessler’s solution, which become brown if
 there is any ammonia in the air.

=Microscopical Examination= is required for the detection of suspended
matters. These are the most potent for harm, containing sometimes
the germs of infectious diseases. The suspended matters scattered
throughout the air may be collected by Pouchet’s aeroscope. This
consists of a small funnel drawn out to a fine point, under which a
slip of glass is placed moistened with glycerine. Both funnel and
glass are enclosed in an air-tight chamber, connected by tubing with
an aspirator, by means of which when water is allowed to escape from
it, air is drawn through the funnel and its particles impinging on the
glycerine are there arrested. Glycerine may be objectionable from the
foreign particles previously contained in it. Various other plans have
been devised, one of which is to draw the air through a small quantity
of pure distilled water and then examine a drop of it. By microscopic
examination large particles can be detected. For the detection of
bacteria and their spores more delicate methods are required.

The =Bacteriological Examination= of air is usually conducted as
follows. Air is drawn through a wide glass tube (Hesse’s tube), which
has been previously sterilised, and on the inner side of which liquid
gelatine has been allowed to solidify. The air as it passes over the
gelatine deposits any germs present in it. The entrance of any further
germs is prevented by closing the tube, and it is then left to stand
for two or three days. Moulds and colonies of bacteria will develop
in the gelatine, and these can be counted and differentiated by their
appearance and by further tests. In closed rooms the number of microbes
(_i.e._, bacteria and moulds) ought not to be more than 20 per litre of
air in excess of those in the outside air; and the ratio of bacteria to
moulds ought not to exceed 30 to 1.

=Examination of Temperature and Moisture.=—The temperature should be
observed at the point most remote from an open fire-place, and compared
with the external temperature. For methods of estimating moisture, see
page 240.

It may be useful to recapitulate at this point the desiderata in an
inhabited room. The temperature should be 60-62° Fahr., the amount of
carbonic acid should not exceed ·06 per cent. and the humidity should
range between 73 and 75 per cent. of the amount required to produce
saturation. The dry bulb thermometer should read 63-65° Fahr., the wet
bulb 58°-61° Fahr., and the difference between the two should not be
less than 4° or more than 8°.



In addition to the artificial measures which will be discussed in the
next chapter, various natural agencies are constantly at work for
the removal of the impurities discussed in preceding chapters. Of
these, the most important are the action of plants, the fall of rain,
natural methods of ventilation, and certain natural constituents of the

1. =Plants=, by virtue of the chlorophyll contained in their green
parts, absorb carbonic acid from the atmosphere, liberating oxygen in
an active condition. In addition, ammonia and nitrous and nitric acids
are dissolved from the air by rain-water, and assimilated by plants.
During the night plants only give off carbonic acid.

2. =The Fall of Rain= clears the atmosphere of any solid particles
contained in it, the impurities being transferred to rain-water which
generally contains an appreciable amount of ammonia as well as other
impurities. Rain not only washes and purifies the air, but by washing
the ground, diminishes dust, and prevents its escape into the air. It
is the great natural scavenger.

3. =Ventilation=—that is, the interchange of pure and impure air,
is constantly being effected. Before entering on the details of
ventilation, we must consider the _physical causes_ at work which
tend to purify the air, apart from all artificial contrivances. These
are three in number—namely, diffusion, winds, and differences of
temperature of masses of air.

(1) =Diffusion= causes the rapid mixture of gases placed together.
Every gas diffuses at a certain rate—namely, inversely as the square
root of its density. In any room which is not air-tight, diffusion
is constantly occurring, air passing in and out at every possible
point. Through chinks and openings in the carpentry-work of a room,
the air diffuses rapidly. Bricks and stone commonly allow air to pass
through them; diffusion occurs to a slight extent even if the wall is
plastered, but very little through paper. Diffusion alone is quite
insufficient to purify a room under ordinary circumstances; and solid
particles including the organic matter evolved from the skin and lungs,
not being gaseous, are unaffected by it. To remove these, the room must
be periodically flushed with air, and washing of all dirty surfaces
must be carried out.

Diffusion sometimes produces evil results, when the sanitary
arrangements of a house are bad. If there is a leakage of sewage under
the kitchen floor, the foul gases from it diffuse upwards; occasionally
foul air diffuses from the dust-bin through the wall into the rooms
of a house. These results are helped by the fact that the internal
temperature of a house is commonly higher than the external.

(2) =Differences of Temperature= cause active movements of air. In fact
winds are caused by movements between large masses of air of unequal
temperature and consequently of unequal density. Light gases ascend, as
familiarly illustrated by the smell of dinner perceived in bedrooms,
or the smell of a cigar lit in the hall perceived in the attic. In
rooms differences of temperature of the air are caused by the heat of
fire, gas, and our own bodies. Currents of air result; the warmer and
lighter air ascends up the chimney or towards the ceiling, while colder
and denser air rushes in under the door or through the floor, etc.
The lighter gases carry with them solid particles in suspension and
thus tend to remove the most important impurities. Assuming that the
external air is colder, if admitted into the lower part of a room, it
produces a draught; if admitted at the top of a room, being heavier, it
falls by its own weight on the heads of those in the room. The problem
of ventilation is to secure a sufficient interchange of air without the
production of perceptible currents.

Movements of air are constantly occurring, so long as the temperature
of the air is subject to changes. This cause alone will suffice to
ventilate all rooms in which the air is hotter than the external air.
It may thus happen that a room with windows and doors closed in winter,
may possess purer air than the same room in summer with these thrown
widely open. The value of diffusion of air through the walls, and the
influence of temperature on this diffusion are well illustrated by some
experiments of Pettenkofer.

 When the difference between the outside and inside temperatures was
 34° Fahr. (66° inside and 32° outside), and the doors and windows were
 shut, an ordinary room in his house, of the capacity of 2,650 cubic
 feet, which was built of brick, and furnished with a German stove
 instead of an open fire-place, had its entire atmosphere changed once
 in an hour. With the same difference of temperature, but with the
 addition of a good fire in the stove, the change of air rose to 3,320
 cubic feet per hour. On lessening the difference between the external
 and internal temperature to 7° Fahr. (64° and 71°), the change of air
 was reduced to only 780 cubic feet per hour. In these experiments, all
 crevices and openings in doors and windows were pasted up.

It is instructive to note the greater amount of ventilation effected
through the walls, etc., than by the draught of the stove.

The amount of ventilation through walls varies with the material of
which they are built. Mortar is exceedingly porous when dry; sandstones
and bricks are easily permeated by both water and air. Limestone is
almost impervious to air, but requires much mortar in building, which
effects a partial compensation (see page 206).

The rise of temperature caused by the bodily heat and by the combustion
of illuminating agents, is well shown by some figures of Dr. Angus
Smith. He found that the rise of temperature of 170 cubic feet of air
in one hour, produced by the bodily heat of one man was 5°·6 Fahr.; by
the combustion of a candle 3°·8 Fahr. Thus, in a room 8 feet high, 4
feet broad, and 6 feet long, a man burning a candle would in an hour
raise the temperature from 60° to 70° Fahr. This rise in temperature
would not only cause currents of hot air towards the upper part of the
room, but would probably make the room uncomfortable, and so lead to
the opening of a door, etc.

(3) =Winds= are of great value in flushing rooms with fresh air. They
ought to be utilised as often as possible, by throwing windows widely
open; without, however, taking the place of constant ventilation in
the intervals. They are especially valuable in getting rid of organic
matters which are unaffected by diffusion.

The wind will pass through wood, and even brick and stone walls. When
it is allowed to pass directly through a room, as from window to door,
it produces a more powerful effect than can be produced in any other
way. The average rate of movement of winds in this country is 10 feet
per second, or about 7 miles an hour. If the surface which a man
exposes to this average wind = 6’ × 1½’ = 9 square feet, then 90
cubic feet of air flows over him in one second, and 324,000 in an hour.
If 3,000 cubic feet were the allowance for each person indoors—a much
greater allowance than is usually given—he only receives 1∕108 of the
air with which he is supplied in the open.

Winds act as a ventilating agent in two ways—=directly by perflation=,
driving impure air before them, or freely mixing with it; and
=indirectly by aspiration=, drawing the impure air along with them. In
the last case, the wind causes a partial vacuum on each side of its
path, towards which all the air in its vicinity flows. Thus, the wind
blowing over the top of a chimney causes a current at right angles
to itself up the chimney. In a spray-producing apparatus we have a
familiar instance of the same principle, the current of air or steam
along the horizontal tube causing the fluid to rise in the vertical
tube till it is scattered in spray. In Sylvester’s plan of ventilation,
both these forces are used (see page 150).

4. =Certain Constituents of the Atmosphere= have an important purifying
effect. Of these oxygen is by far the most important. By its means
organic impurities become oxidised, and thus rendered harmless. It is
probable that much of this oxidation is effected by means of ozone—a
peculiarly active and concentrated form of oxygen. A large part of this
ozone is probably produced during thunderstorms and similar electrical
disturbances of the atmosphere. The ammonia and organic impurities in
air become changed into nitrites and nitrates—chiefly of ammonium—and
being washed down by rain, form an important part of the food of plants.

5. =For Chemical Measures= of purification of the atmosphere see page



=The Amount of Air required.=—Ventilation is chiefly concerned with
the removal of the products of respiration, just as sewage is chiefly
concerned with the removal of the solid and liquid excreta.

In a less degree it is required for removing the impurities produced by
the burning of gas, candles, and lamps. The main problem, however, is
the removal of the respiratory products.

The amount of carbonic acid in air is usually fairly proportional to
that of the other respiratory products. It may therefore be taken as
a measure of the impurity of the air. There are, however, certain
fallacies in this test. In soda water manufactory, for instance, there
would be a comparatively harmless excess of carbonic acid. In dirty
rooms, and in hospitals and other institutions where rooms are not
vacated for a considerable period, the amount of organic matter present
is often in excess of what would have been anticipated, judging by
an estimation of the carbonic acid. This is strikingly shown by some
valuable researches at Dundee, which are summarised in the following
table. If we take the average amount (in excess of outside air) of
carbonic acid, organic matter, and micro-organisms respectively in
houses of four or more rooms as unity, then in one or two-roomed houses
or tenements we have as follows:—

  │                  │    ROOMS     │ HOUSES.  │ HOUSES.  │
  │                  │ AND UPWARDS. │          │          │
  │_Carbonic acid_   │      1       │   1·5    │   2·0    │
  │_Organic matter_  │      1       │   1·6    │   4·4    │
  │_Micro-organisms_ │      1       │   5·1    │   6·7    │

It is evident that in these cases the carbonic acid did not increase in
the same proportion as the organic matter and micro-organisms, and that
it alone does not form a sufficient test of the impurity of any given
atmosphere. The amount of carbonic acid, however, is a valuable and
convenient test of the condition of the air of a room, and the problems
of ventilation, of which examples are given on page 137, are based on
its amount.

The =Standard of purity= is somewhat difficult to fix. The external air
ought only to contain 4 parts of carbonic acid to 10,000 parts; but
it is almost impossible to maintain this degree of purity in inhabited
rooms. The experiments made by Drs. Parkes and De Chaumont showed that
when the carbonic acid is ·06 per cent., or in the proportion of 6
parts in 10,000 of air, the air begins to be perceptibly stuffy (page
125); this may therefore be taken as the limit of impurity. Pettenkofer
has adopted the limit of ·07 per cent.[7]

The problem then is to discover the amount of pure external air
(containing ·04 per cent. of carbonic acid) that will be required to
pass hourly through a room, for every person in that room, in order to
keep the carbonic acid at the ratio of ·06 per cent.

This may be ascertained by actual observation of the air of rooms in
which a given number of persons are placed; or by calculations from
physiological data.

As _the result of numerous experiments_ on the atmosphere of prisons,
barracks, etc., where the amount of fresh air supplied per hour is
exactly known, it is found that in order to keep the carbonic acid at
·06 per cent., 3,000 cubic feet of pure air are required per head per
hour; 2,000 cubic feet keep the carbonic acid at ·07 per cent.; 1,500
cubic feet at ·08 per cent.; and 1,200 cubic feet at ·09 per cent.

For the removal of the products of combustion of gas, an additional
supply of air is required, for the amount of which, see page 116.

Where a number of sick persons are collected, as in hospitals and
workhouses, a much freer supply of air is required. Much depends,
however, on the cleanliness of the wards, and on whether the
ventilation is constant in character. In St. Thomas’s Hospital, the
space allotted to each ordinary patient is 1,800 cubic feet, and to
each patient in the fever wards 2,500 cubic feet. Thus, by changing the
air of the wards twice in the hour, an abundant supply of fresh air is
ensured. The mortality after operations, and in all fevers, is much
diminished by a free supply of air.

Soldiers are allowed 600 cubic feet of space per head in their sleeping
rooms, which involves a change of the air five times per hour, in order
that the carbonic acid may be maintained at ·06 per cent. The limit of
overcrowding for lodging-houses is usually fixed at 300 to 500 cubic
feet, but this is too little.

The amount of pure air required in order to keep the carbonic acid in
a room at ·06 per cent., may also be ascertained from _physiological

An average adult expires 3∕5 (·6) cubic foot of carbonic acid per
hour. Now as the carbonic acid in air to be breathed must not contain
more than two parts in 10,000 (·02 per cent.) in excess of what is
present in external air (·04 per cent.), it follows that if _x_ = the
amount of fresh air required by an adult per hour in order to keep the
carbonic acid in the room down to .06 per cent., then:—

  ·02 : ·6 :: 100 : _x._
  _x_ = 3,000 cubic feet.

=Relation of Air Required to Cubic Space of Room.=—If we accept 3,000
cubic feet of air as the amount required per head per hour, this
may clearly be furnished by having a large room with comparatively
little circulation of air, or by having a small room with frequent
interchanges. Thus, supposing the cubic space allowed to each
individual is 1,000 cubic feet—that is, 10 feet in every direction—the
atmosphere will require changing three times per hour.

Now, it is found that when a current of air, at the temperature of
55°-60° Fahr., is moving at the rate of less than one mile per hour, it
is not perceptible—that is, produces no draught. The rate of a breeze,
which is just perceptible, is 18 inches per second, or one mile per
hour. As draughts are objectionable, ventilation, in the best sense of
the word, means the supplying of abundant fresh air at a rate of less
than one mile per hour, or warmed air at a higher rate. Air moving
at the rate of 2½ miles per hour, or 3½ feet per second, is
perceived as a slight draught by all, at the average temperature of our
climate (about 50° Fahr.)

Where natural ventilation is employed, the difficulties of thoroughly
ventilating a small space, without draught, are very great.

A change of air three or four times in an hour is all that can be
borne under ordinary conditions in this country, and this necessitates
a supply of 1,000 or 750 cubic feet of space respectively for each
individual. And a change of this frequency is commonly not effected;
the ventilating apparatus may fail temporarily, or may be wilfully
stopped up, or there may be no means of ventilation; it is essential
therefore to have as large a cubic space as possible. A large cubic
space, does not obviate the necessity for efficient circulation of air.
It is, however, advantageous, not only on account of the initial longer
time before the air reaches the limit of impurity, but also because
there are less draughts, and there is a larger wall surface and larger
windows for unperceived ventilation.

=Common Errors as to Ventilation.=—(1) In relation to the cubic space
of a room, it is most important to note that a _lofty ceiling does
not compensate for deficiencies in floor-space_. One hears, “lofty”
and “airy” rooms spoken of as though the two terms were necessarily
synonymous. This is by no means the case. The impurities produced by
respiration tend to accumulate about the persons who have evolved them,
although it is true that in rooms heated by gaslight, a large amount
of hot and impure air collects near the ceiling. The necessity of an
abundant floor-space is shown by the fact that a space enclosed by
four high walls and without a roof, will, if crowded, speedily become
offensive. Twelve feet is quite high enough for large rooms in schools,
hospital wards, etc., and nine feet suffices for the rooms of a private
dwelling-house. There is no objection to a greater height, if it is
remembered that in reckoning the _practical_ cubic dimensions of a
room, the height should only be reckoned as twelve feet. Supposing 500
cubic feet is the amount allowed per individual, then the floor-space
should be forty-two square feet, which would be furnished by a room
about 8½ feet long and 5½ feet wide. In barracks, soldiers
are allowed fifty square feet of floor-space. In school-rooms the
Education Code requires that at least ten square feet of floor-space,
and at least 120 cubic feet shall be allowed for each child in average

(2) It is commonly supposed that a large room compensates for a
deficient circulation of air. _The cubic space of a room is really of
less importance than the capacity for frequent interchanges of air._
Even the largest enclosed space can only supply air for a limited
period, after which the same amount of fresh air must be supplied,
whether the space be small or large. Thus, supposing that as large a
space as 10,000 cubic feet per head were allowed, the limit of purity
would in the absence of ventilation be reached in three hours, and
after that time an hourly supply of 3,000 cubic feet of air would be
just as necessary as if the space were only 200 cubic feet.

(3) It must not be overlooked that the _furniture in a room_ must be
deducted from the breathing space, as the amount of air is diminished
by the space occupied by the furniture. About 10 cubic feet ought to
be allowed for each bed, and 3 to 5 cubic feet for each individual in
a room; projecting surfaces must be allowed for by subtraction, and
recesses by addition. The deductions to be made for furniture are not
of any great consequence, if there is a free interchange of air; as the
cubic space is of less importance than free ventilation.

=General Rules respecting Ventilation.=—The two great objects in
ventilating being to remove all impurities from the air, and to avoid
draughts, it is important that—

1. _The entering air should be, if possible, of a temperature of 55°
to 60° Fahr._ Whenever the temperature of a room differs from the
external temperature by 10° Fahr., a draught is certain to ensue. It
is impossible at all times to ensure the incoming air being of the
temperature of 60°, without some artificial means of warming it. In
this country it is seldom necessary to cool the incoming air, but this
may be managed in artificial systems of ventilation by passing the
incoming air over ice, or by using compressed air which becomes cooled
on expansion, or by passing the incoming air through subterranean

2. _The entering air should be pure._ When a room is hotter than
the passages and kitchens, air from the latter, whatever may be its
character, is drawn into the room. Similarly the ground-air under the
kitchen-floor or the air from ash-pits may be drawn into the house,
when no other means of ventilation are provided; and this is often
followed by evil results.

3. _No draught or current should be perceptible_ from the incoming air,
except when it is wished to flush the room with air, by opening the
windows wide. It is a common complaint that a room is draughty, and, to
remedy this, keyholes are stopped up, and mats are placed at the bottom
of the door, etc. The draught can often be remedied by increasing the
size and number of the openings through which air is admitted, so that
the current of air is not concentrated and rapid. When this does not
remedy it, the incoming air should be warmed. A feeling of draught is
very often due to the radiation to and from a window, and disappears
when a curtain or screen is placed between the radiating surface and
the occupant of the room.

4. _The entry of air should be constant, not intermittent._ The
occasional opening of a window or door will not compensate for the lack
of a constant interchange of air, although it forms a very valuable
adjunct, especially in the removal of organic particles which do not
follow the law of diffusion.

5. _An exit should be provided for impure air_, as well as an entrance
for pure air. The chimney furnishes this in most living-rooms, and
diminishes the necessity for other means of exit.

If the openings in a room for entrance and exit are properly regulated,
a rate of 5 feet per second (about 3½ miles per hour) will provide
sufficient air without any unpleasant draught in a room. For instance,
if the opening measure 1 square foot, then a rate of 5 feet per second
will give five cubic feet of air per second, that is, 18,000 cubic feet
per hour. But as only 3,000 cubic feet are required, it follows that
an opening one-sixth this size, _i.e._ 24 square inches, is sufficient
for each individual. Reckoning the same amount for means of exit, 48
square inches is the size of the ventilating orifices required by each

6. _A number of small divided openings are not collectively equal in
ventilating power to one large one having the same area._ Thus, when
a ventilating orifice is divided into four parts, which have the same
collective area as the original orifice, it is found that only half as
much air passes through these as through the original orifice. In order
to obtain as much air, therefore, each opening must be equal in size to
half the original opening. This is in accordance with the rule that the
friction for air passing through openings is inversely to the diameter
of these openings, _i.e._ inversely to the square-root of the area of
the openings.

7. The most important requirements of perfect ventilation may be
recapitulated as follows:—

1st. The maximum impurity of air vitiated by respiration should not
exceed 6 parts carbonic acid per 10,000 volumes.

2nd. To ensure the maintenance of this standard, 3,000 cubic feet of
pure air must be supplied per head per hour.

3rd. In order to supply this amount of pure air, with ordinary means
of ventilation, 1,000 cubic feet at least must be allowed per head in
buildings always occupied.



The following formula enables many problems relating to ventilation to
be solved. Let p = the amount of poison (carbonic acid) in every cubic
foot of fresh air, viz. ·0004 cubic foot. Let A = the number of cubic
feet of fresh air delivered or available, P = the amount of carbonic
acid exhaled, and x = the amount of carbonic acid per cubic foot in the
room at the end of a given time. Then—

  x = p + P/A, whence A = P/(x - p).

_If the carbonic acid in the air of a room is ·75 per 1,000 volumes
(that in the outer air being ·4 per 1,000 volumes), and there are five
persons in the room, how much air is entering the room per hour?_

  Here x = ·00075.
       p = ·0004.
       P = ·6 (_i.e._ number of cubic feet of carbonic acid expired by
                        each person per hour).
   Now x = p + P/A.

     ·00075 = ·0004 + ·6/_A_.

  Therefore _A_ = about 1,700.

Thus 1,700 cubic feet are required for each individual to keep the air
within the given limit, and five times this amount will be required for
five persons = +8,500+ cubic feet.

_A room has been occupied for one hour, at the end of which the total
carbonic acid present was found to be 1·1 per 1,000 parts. The carbonic
acid in the open air amounting to ·0004 per cubic foot, find the
quantity of air supplied per hour._

  Here x = ·0011.
       p = ·0004 and P = ·6.

  Hence ·0011 = ·0004 + ·6/A.

  Therefore A = +857+ cubic feet.

_If six persons are in a room containing 3,000 cubic feet, and there
is a supply of 2,000 cubic feet of air per head per hour; how much
carbonic acid is there in the air of the room at the end of 4 hours?_

  Here p = ·0004.
       P = ·6 × 6 × 4 = 14·4.
       A = 2,000 × 6 × 4 + 3,000 = 51,000.
       x = ·004 + 14·4∕51,000 = ·000682 = 6·82 parts CO₂ in 10,000
                                                            of air.

_The air of a room occupied by 6 persons and containing 5,000 cubic
feet of space, yields 7·5 parts of CO₂ per 10,000 parts of air. How
much air is being supplied per hour?_

  A = P/(x - p) = ·6 x 6/(·00075 - ·0004) = +10,280+ cubic feet.

_In the same room what would be the condition of the air at the end of
4 hours?_

  x = ·0001 + ·6 × 6 × 4/(10280 × 4 + 5,000)

      = ·0004 + 14·4∕46,120 = ·000712 = +7·12 of CO₂+ in 10,000 of air.

_Given two sleeping rooms, Y 10 ft. by 15 ft. and 10 ft. high, Z 15 ft.
by 20 ft. and 12 ft. high, with three adults in each; how much fresh
air would you supply in each? What would be the condition of the air of
each of the rooms after, 1∕4, 1∕2, 1, and 2 hours respectively?_

  Amount of fresh air to be supplied in _Y_—

  A = P/(x - p) = ·6 × 3/(·0005 - ·0004) = _9,000_ cubic feet per hour.

  Condition of air in Y after 1∕4 hour—
                   Here p = ·0004.
                        P = ·6 × 3∕4 = ·45.
                        A = 9,000∕4 + 1,500 = 3,750.
         x = ·0004 + ·45∕3,750 = +·00052+.

  At the end of 2 hours—
         x = ·0004 + 3·6/(18,000 + 1,500) = +·000584+.

  And similarly for Z.

_Suppose two rooms, one 10 feet cube, the other 50 feet by 20 feet and
15 feet high, have continuously admitted into each of them a volume of
fresh air containing ·04 parts carbonic acid per 100 parts, amounting
to 2,000 cubic feet per hour, so as to replace to that extent the air
of the room; suppose also that an average adult be placed in each room:
show by detailed calculation what would be the condition of impurity of
air in each room, as measured by carbonic acid, at the end of 4 hours
and 12 hours respectively._

  In the case of the first room—
        P = ·6 × 4 = 2·4.
        A = 2,000 × 4 + 1,000 = 9,000.
        p = ·0004.
        x = ·0004 + 2·4∕9,000 = +·000667+.

The amount of impurity at the end of 12 hours, and in the second room
may be similarly ascertained.

=Ventilation in relation to Temperature.=—The temperature of a given
atmosphere is a most important factor in determining the ease with
which it is replenished from the external air. Speaking generally, the
greater the difference between the temperature of two masses of air the
more rapidly an interchange occurs.

Air has weight. A column of it one inch square and extending to the
uppermost limit of the atmosphere weighs about 14·6 lbs., and exerts
this pressure on all substances at the surface of the earth. This
pressure is exerted uniformly in all directions; but for this fact our
chests would be crushed in by the external pressure on them, which
amounts to over four tons. If the atmospheric pressure is diminished at
any point, it is evident that the surrounding air will tend to press in
this direction. Now, when air is heated it expands, and consequently
the heavier fresh air flows in from all sides and pushes the lighter
air upwards.

 The expansion of air for every increase of 1° Cent. is ·003665
 (1∕273), for every increase of 1° Fahr. is ·00203 (1∕492). Thus if the
 air in a room is 20° F. warmer than that outside, it will be expanded
 to 1∕25 additional bulk.

 Thus if M = volume of a given air at 32°, with the barometer at 30
 inches, and M₁ = volume at temperature t° above 32°, while _a_ =
 co-efficient of expansion for each degree of elevation of temperature,
 then the dilatation effected by heat will be expressed by the formula—

 M₁ = M (1 + at).

 When the temperature is decreasing

 M₁ = M (1 -at).

If the air in a chimney flue is cooler than the air of the room with
which it communicates, it will flow down into the room. It is the
object of an economical fire-place to cause the chimney to act as
an outlet for the products of combustion and for the impurities of
the air of the room with the smallest possible waste of heat. Short
of producing a down draught of cold air and smoke, the smaller the
difference between the temperature of the air of a room and of the air
escaping near the top of the chimney, the greater the economy of fuel.

The =movement of air in flues and other outlets= is governed by general
laws, like those governing the general movements of fluids, but
allowances require to be made for friction in the channels of entrance
and outlet.

The theoretical velocity, when friction is not taken into account,
may be calculated by a formula based on what is known as the _law of
Montgolfier_, or the law of spouting fluids. According to this law,
fluids pass through an opening in a partition with the same velocity as
a body would attain in falling through a height equal to the difference
in depth of the fluid on the two sides of the partition, _i.e._ to the
difference of pressure on the two sides. Thus, if AB equals the height
of a column of air at, say, 50° F., and AC is the height of the same
quantity of air heated to 60°, then the velocity with which the warmer
air ascends will be that which a body would acquire in falling from C
to B.

[Illustration: Representing the air column lengths]

Now the velocity in feet per second of falling bodies is about eight
times the square root of the height from which they have fallen; and
the formula for determining this is—

 v = c √(2gh) = 8·2c √h.

 In this formula v = required velocity in feet per second;

 g = 32·17 feet per second;

 h = distance fallen through by the body;

 c = a constant determined by experiment, and expressing the proportion
 of the actual to the theoretical velocity.

Adapting this formula to the special circumstances under which
Montgolfier’s formula holds, we find that the force which drives the
warm air up the flue is the force of gravity, _i.e._ of the excess
of the weight of a column of cold air over the weight of a column of
warm air of exactly the same size (represented by BC in the preceding
diagram). The difference of the two weights or pressures is found by
multiplying the distance from the point of escape of heated air out
of the room (fire-place or elsewhere) to the point of escape into the
outer air (top of chimney or other point of exit), by the difference
in temperature inside and outside, and again multiplying this product
by 1∕492 for degrees of Fahrenheit temperature, or 1∕273 for degrees

  Thus omitting c for the present, we have—

  v = √(2g_h_(t - t^1)/492) = 8·2√(h(t - t^1)/492)

  Where t = temperature in the chimney,

  t^1 = temperature of the external air, and

  h = height of chimney.

_Example.—The chief means of ventilating a given room is by its open
fire-place. The temperature in the chimney is 100° F., that of the
external air 40°, and the height of the chimney 50 feet; what is the
velocity with which air is leaving the room?_

  v = 8·2 √((100 - 40) × 50∕492)

  = +20+.

This gives the theoretical velocity, but the real velocity will differ
from the theoretical by an amount varying from 20 to 50 per cent.

It will be evident, from what has been said, that the movements of the
air in a confined space are dependent upon (1) the difference between
the internal and external temperatures; (2) the area and friction at
the apertures through which air enters and leaves the room; and (3)
the height of the column of ascending warm air. The higher the chimney
(assuming it to contain warm air), the greater the draught and the more
efficient the ventilation of the room communicating with it. Hence
ventilation is more difficult in upper rooms of large houses and in
single-storeyed houses than in the lower storeys of large houses.

=Allowance for Friction.=—Practically the friction varies greatly
according to the size, form, and material of outlet for air. A rough or
sooty or angular chimney greatly impedes the outgoing current of air.

It is usual to reduce the theoretical velocity by 20 to 50 per cent.
Apart from the friction which is governed by roughness and length of
channels, that due to bends in the channel may be calculated by the
formula 1/(1-_sin_^2 θ), θ being the angle at any bend in this channel.

  (It may be convenient to note that—

  _sin_^2 90° = 1,
  _sin_^2 60° = 3∕4,
  _sin_^2 45° = 1∕2,
  _sin_^2 30° = 1∕4.)

Thus every right angle in a bent shaft reduces the velocity in it by

The loss by friction in two similar tubes of equal sectional area
varies (1) directly with the square of the velocity of the air
currents; and (2) directly with the length of the outlet channel. In
two similar tubes of unequal size the loss by friction is (3) inversely
as the diameter of the cross-section in each.

When two tubes are of different shapes, the loss by friction is
inversely as the square roots of the sectional areas.

Owing to the variable value of the co-efficient of friction (called
_c_ in the first formula given), it is usually preferable to measure
the actual rate of progress of air through a given flue by means of an
anemometer (wind measure). Then the velocity of the current of air and
the area of the cross section of the flue being given, the volume of
air discharged in a given time is represented by the product of these
two and the time which has elapsed.

 Thus, q = a × v.

Where q = quantity of air discharged in a given time, a = area of cross
section of flue, v = velocity of current.

By means of this formula, the area of chimney required to discharge a
given volume of air at a given average velocity can be ascertained.

  a = q/v.

The application of the preceding principles and formulæ will be
rendered clearer by the following examples.

_How much inlet and outlet area per head will be required to give 10
persons in a room of 5,000 cubic feet capacity, 2,000 cubic feet of air
per head per hour, supposing that the outside temperature is 40°, while
the internal temperature is 60°, and the height of the heated column of
air 20 feet?_

First ascertain the velocity of entrance and exit of air.

  v = 8·2√(h(t - t^1)/492)

           = 8·2√(20(60 - 40)/492) = 8·2 × ·902.

           = 7·3964 = velocity in feet per second.

If we allow one-fourth for friction, then there remains a velocity of
5·5473 feet per second.

  5·5473 feet per second = 19700·8 feet per hour.

  Now, a = q/v

                = 2,000∕19700·8 = ·1015 square feet.

                = +14·6 square inches.+

Thus the size of the outlet required per head is 14·6 square inches.
The size of the room and the number occupying it do not enter into the
question, except for a short time at the beginning. (See page 135.)

The amount of inlet required will also be 14·6 square inches per head.
Theoretically it ought to be slightly less than that required for
outlet, as the outgoing air is more expanded than that entering the
room; but practically no allowance need be made for this fact.

The total amount of inlet and outlet required per head = +29·2 square

_If the mean temperature of a room is 61°, the external temperature
45°, while the heated column of air is 50 feet, and the required
delivery of air 2,000 cubic feet per hour, find the size of inlet and

  v = 8·2√(h(t - t^1)/492)

           = 8·2√(50(61 - 45)/492)

           = _10·55 feet per second._

           = _37,980 feet per hour._

If we make no allowance for friction, then

  a = q/v

                  = 2,000∕37,980 square feet.

                  = 2,000 × 144∕37,980 = 7·58 square inches.

This gives the required size of outlet. The size of inlet and outlet
together = _15·16 square inches._

_If 3,000 cubic feet of air are supplied in one hour through an
aperture of 12 square inches to a room containing 1,000 cubic feet of
space, at what rate does the air enter the room?_

  12 square inches = 1∕12 square foot.

            a = q/v

                1∕12 = 3,000/v

  Therefore v = 36,000 feet per hour.

                     = _10 feet per second._

_If a room is supplied with 3,000 cubic feet of air per hour, through a
single opening, what must be its area, if the rate of movement of the
air is 5 feet per second?_

  5 feet per second = 18,000 feet per hour.

          a  = 3000∕18000 = 1∕6 square foot.

                    = _24 square inches._

As already stated, the difficulties connected with the estimation of
amount of friction greatly detract from the practical value of the
formulæ just given. Even the results given by anemometers are not
always trustworthy, but by comparing the results given by them with
those obtained by the use of Montgolfier’s formula an approximation to
the truth can be obtained.

The ordinary _anemometer_ consists of four tiny vanes fixed to a
spindle, so that revolutions are caused by the current of air the
velocity of which is to be measured. The revolutions are counted by
a mechanical arrangement. The value of the revolutions of the vanes
has to be first determined by direct experiment; a known bulk of air
being forced through a channel of known size at a uniform rate, and
the instrument graduated accordingly. In Fletcher’s anemometer a
modification of the manometer or pressure-gauge has been used for the
same purpose.

=Inlets and Outlets.=—Having given the average velocity of the wind,
the size of a room, and the number of persons occupying it, the size of
inlet opening required can easily be calculated.

_Find the size of inlet for air in a room occupied by one person, the
air moving at the average velocity of 5 feet per second, assuming that
3,000 cubic feet of air are to be supplied per hour._

  Let x = size of inlet.

  Then x × 60 × 60 × 5 = 3,000.

  Therefore x = 3000∕18000 = 1∕6 square foot.

                                  = _24 square inches._

_Given that the air moves at a velocity of 10 feet per second, and that
the area of the inlet aperture into a room is 12 square inches, find
how much air enters the room in an hour._

  Let y = amount of air.

  Then 10 × 60 × 60 × 12∕144 = y.

  Therefore y = 3,000 cubic feet of air.

Calculations as to supply of air in a room founded on the _average_
velocity of air-currents are, however, much less trustworthy than
when the velocity is determined, as previously explained, by means of
Montgolfier’s formula, or, better still, by an anemometer.

The Commissioners on Improving the Sanitary Condition of Barracks and
Hospitals, in their report (1861) recommended for _inlets_, one square
inch for every 60 cubic feet in the contents of the room; or one square
inch for every 120 cubic feet in the contents, if warm air is admitted
round the fire-grate. For _outlet_ shafts on lower floors, one square
inch to every 60 cubic feet, slightly increasing for the higher storeys.

=Amount of Air-space required.=—We may take 3,000 cubic feet of air
as the average amount of air required hourly by each individual, and
inasmuch as the air of a room cannot be changed oftener than three
times an hour without producing an unpleasant draught, it follows that
at least 1,000 cubic feet of space must be allowed per person.

 This may be compared with the amount actually supplied under various

  In the British Army for each soldier—
    In permanent barracks                               600 cubic ft.
    In wooden huts                                      400   „
    In hospital wards at home                         1,200   „
    In hospital wards in the tropics                  1,500   „

    In general hospitals                        1,000-1,500   „
    In fever hospitals                          2,000-3,000   „
    In workhouse hospitals                        850-1,200   „
    In common lodging houses                     300 or 350   „
    Do., if occupied night and day               350 or 400   „
    In workhouses                                       300   „

  In schools—
    London School Board requires per scholar            130   „
    English Educational Code per scholar (minimum), in
      old schools                                        80   „
    Do., in new schools                                 120   „

_Floor-space_ has an important bearing on ventilation. In calculating
the available cubic space of a room, the height over 12 feet should be
disregarded. Thus, if 500 cubic feet is allowed for each individual,
the floor-space should be 42 square feet. In barracks, soldiers are
allowed 50 square feet of floor-space.

In the Government regulations for workhouses it is stated that there
must not be more than two rows of beds, and that the height of rooms
above 12 feet must not be reckoned. This gives a minimum floor-space
of 25 square feet per occupant, or with dormitories 17 feet wide, a
bed-space of about 3 feet.

In hospitals, the question of floor-space is extremely important, as it
regulates the distance between the sick inmates and the convenience of
nursing. Assuming each bed to be 3 feet wide and 6½ feet long, the
distance between any two beds should be at least 5 feet. This makes the
wall-space for each bed 8 feet long, and allows from 80 to 96 square
feet of floor-space per bed. At St. Thomas’s Hospital, London, the
floor-space is 112 square feet, and in fever hospitals it is from 150
to 300 square feet per bed. In regard to the ventilation of hospitals,
it has been well said that nothing less than too much is enough.

=Means of ascertaining Cubic Space.=—Circumference of a circle =
Diameter (D) × 3.1416.

 Area of circle = D^2 × .7854.

 Area of square = square of one of its sides.

 Area of rectangle = product of two adjacent sides.

 Area of triangle = base × 1∕2 height, or height × 1∕2 base.

 Area of ellipse = product of the two diameters × ·7854.

 Circumference of ellipse = half the sum of the two diameters × 3·1416.

 Area of any polygon found by dividing into triangles, and taking the
 sum of their areas.

 Cubic capacity of a cube found by multiplying the three dimensions

 Cubic capacity of a cylinder = area of base × height.

 Cubic capacity of a cone or pyramid = area of base × 1∕3 height.

 Cubic capacity of a dome = area of base (circle) x 2∕3 height.

 Cubic capacity of a sphere = D^3 x ·5236.

 Area of segment of a circle found by adding to 2∕3 of product of chord
 and height, the cube of the height divided by twice the chord.

  (Ch x H x 2∕3) + H^3∕2 Ch

_Give the dimensions of a circular ward for 12 patients, each to have
1,750 cubic feet of available air-space._

Capacity of ward = 1,750 X 12 = 21,000 cubic feet.

If we allow 120 square feet floor-space for each patient, then the
total floor-space will be 1,440 square feet. Consequently the height of
the ward = 21000∕1440 = 14·75 feet.

           Area of circle = D^2 x ·7854.

              1,440/·7854 = D^2.

              Therefore D = +43·2 feet.+

  Circumference of circle = D x 3·1416.

                          = 43·2 x 3·1416.

                          = +135·7 feet.+

The dimensions of the circular ward required are therefore a height of
14·75 feet, diameter of 43·2 feet, and circumference of 135·7 feet.

_Find the cubic capacity of a circular hospital ward 28 feet in
diameter, 10 feet high, and with a dome-shaped roof 5 feet high._

  Area of floor-space = D^2 x ·7854.

                      = 614·8 square feet.

  Cubic capacity of the cylinder below the dome is 614·8 x 10
                                                   = 6,148 cubic feet.

  Cubic capacity of dome = 614·8 x 2∕3 x 5 = 2049·3 cubic feet.

  Total cubic capacity of the ward = 8197·3 cubic feet.

In practical measurements of rooms, deductions must be made from the
cubic space for the furniture contained in it and for its inmates.
About 10 cubic feet ought to be allowed for each bed and bedding, and
2½ to 4 cubic feet for each individual. Projecting surfaces must be
allowed for by subtraction, and recesses by addition.

_A circular ward with a diameter of 36 feet has a dome-shaped roof, the
height of whose centre is 18 feet. The height to the dome is 12 feet.
Find the floor-space and total cubic contents. How many patients ought
the ward to accommodate?_

  Area of floor-space = (36)^2 x ·7854.

                      = 1017·8784 square feet.

  Cubic capacity of cylinder below dome = 1017·87 x 12
                                                  = 12214·5 cubic feet.

  Cubic capacity of dome = 1017·87 x 2∕3 x 6 = 4071·48 cubic feet.

  Total cubic capacity of the ward = 16285·98 cubic feet.

Assuming that 1,500 cubic feet are required for each patient, then
the ward is large enough for 10 _patients_. It is well to test this
conclusion by calculating whether sufficient floor-space has been
allowed for each patient. The floor-space has been found to be about
1,018 square feet, which would give 100 feet for each of 10 patients
and more than the minimum standard previously stated.

_What number of people should be allowed to sleep in a dormitory 40
feet long, of which the accompanying sketch is a section?_

[Illustration: Outline of rectangular space with triangular roof]

The cubic capacity of the quadrilateral space below the roof = 16 x 9 x
40 = 5,760 cubic feet.

Area of floor = area of base of roof = 40 x 10 = 640 square feet.

  Cubic capacity of roof = 640 x 1∕3(13 - 9). = 853·3 cubic feet.

Total cubic capacity of dormitory = +6613·3 cubic feet.+

If we take the low standard of common lodging houses and allow 350
cubic feet of space for each inmate, then 18 _persons_ may be allowed
to sleep in the dormitory.

_How much space would a man occupy supposing him to weigh 175 lbs.? How
much is usually allowed for a man with his clothes, bed and bedding?_

The space occupied by a man is stated by Parkes to be from 2½ to
4 cubic feet (say 3 for the average). He gives the following rule:
The weight of a man in stones divided by 4 gives the cubic feet he
occupies. Thus, a man weighing 175 lbs. would occupy 3-1∕8 cubic feet
of space.

About 10 additional cubic feet must be allowed for clothing, bedding,
and bed for each person.

_What size of inlet and outlet aperture should be allowed per head? How
large should each individual inlet be made? If an inlet aperture 100
square inches in area is divided into four, with apertures of 25 square
inches each, what is the loss by friction?_

A size of 24 square inches per head for inlet and the same for outlet
meets common conditions.

It is desirable to make each individual inlet not larger than 48 to
60 square inches in area, _i.e._ large enough for two or three men;
and each outlet not larger than one square foot, or enough for six men
(Parkes). This ensures more uniform diffusion of the air throughout
a room. On the other hand, the loss by friction is greatly increased
by having a number of small openings instead of one large opening.
This loss is inversely to the square roots of the respective areas.
Thus the square root of 100 is 10; the sum of the square roots of the
four apertures of 25 square inches each is 20. The loss by friction is
double in the second case what it was in the undivided opening. It is
evident, therefore, that in order to get as much air through the four
openings as through the original large opening, each must be equal in
size to half the original opening.

_Why is ventilation more difficult in upper rooms of large houses and
in single-storied houses than in the lower storeys of large houses?_

Cold external air being heavier than the internal warm air presses
downwards to the lowest point, and pushes up the warmer air. If there
were a vacuum in the room, air would rush into it with a velocity
which, as seen before, is represented by the formula—

v = √(2_gs_).

Where g = 32, s = height of column of air, which we may take as roughly
5 miles.

From this formula we obtain v = 1,306 feet per second.

It is evident that in such a case the velocity of entry of air into a
vacuum on the ground floor would be greater than into a vacuum on any
of the higher storeys, owing to the greater velocity acquired through
the increased action of gravity.

And the same increased facility of entry of air into lower rooms must
hold good under ordinary circumstances, inasmuch as by Montgolfier’s
formula (which is founded on the fundamental formula v = √(2_gs_)

v = √(2_gh_(t-t^1)/492)

h = distance between top of chimney and floor of room in question, and
thus the velocity with which air enters is governed by the difference
between the internal and external temperature, and the height from
which the cold air descends in order to take the place of the air which
has escaped.



In most houses no special means of ventilation are provided, windows,
doors and fire-places being trusted for ensuring a sufficient supply
of fresh air. These do not suffice in well-built houses, unless
the inhabitants train themselves into enduring the currents of air
necessarily associated with open windows and doors. They are, however,
aided in the majority of houses by the porosity of walls, by currents
of air through crevices of wood-work, and so on. It is desirable that
adequate special provision for ventilation should be made for every
house when it is built, and that as much care and forethought should
be exercised in this respect as in the laying on of a water-supply or
sanitary appliances connected with drainage.

Whatever the system of ventilation adopted, it is wise to _flush rooms
frequently with fresh air_. This is best effected by throwing the
windows wide open whenever a room is left unoccupied. In this way a
much more thorough and complete purification is effected than by any
other means. This is especially important in the case of bedrooms, in
which organic impurities are most prone to accumulate.

Not only should rooms be ventilated, but likewise _the furniture_ they
contain. This again is most important for bedrooms. Beds should not be
“made” till sometime after using; and in the interval, should be freely
exposed to the air. The same applies to night apparel.

It is well to allow _rooms to lie fallow_ at intervals. Organic matter
accumulates about a room, and devitalises any air which enters. If
the room is vacated, and flushed with air for a continuous period,
it becomes sweeter and purer. The importance of this is now well
recognised in the case of hospital wards. Such temporary disuse of
rooms must not, however, be regarded as sufficient without thorough
cleansing of every surface in them, in order effectively to remove all
organic and other dust.

=An Inlet and Outlet= for air should both be provided. According to
some an inlet only is required, while others would only provide an
outlet; but a perfect system of ventilation requires both. As heated
air expands, the outlets should theoretically be larger than the
inlets; but as the average difference of temperature is only 10°-15°
Fahr., the expansion is only slight, and may be practically neglected.

The necessity for both inlets and outlets may be illustrated by a
single apparatus like that shown in Fig. 11. A taper is burning at
the bottom of the jar, in the stopper of which two tubes, A and B,
are placed. So long as both tubes are kept open the candle will keep
alight, but if A be blocked, the candle goes out.

[Illustration: FIG. 11.


=Inlets= should bring air from a pure source, and should be arranged
at intervals in large rooms. Externally, inlets should be protected
from the wind; and the shorter the inlet tubes the better, as thus a
current is ensured, and they can be easily cleaned. The position of
inlets should not be too near the outlets, otherwise the fresh air
may escape immediately. The best position for inlets is at the floor,
but this necessitates warming the entering air, as otherwise it would
be intolerable, except in summer time. If the air cannot be warmed,
it should he admitted about seven feet above the floor, and directed
upwards. For size of inlets, see page 142.

=Outlets=, under ordinary circumstances, are best placed near the
ceiling. They should be enclosed as far as possible within walls, so as
to prevent the outgoing air being cooled; and should have smooth walls,
reducing friction to a minimum. Where artificial warmth increases the
temperature of the air, the discharge of outlets is much more certain
and constant. The chimney with an open fire forms one of the best
outlets. Gas, again, may be made to heat an outlet tube, which carries
off the products of combustion.

Two forms of ventilation are usually described—natural and artificial.
The former term is used to describe any plan not requiring heating
apparatus or the motive power of steam, or gas, or electricity, while
the latter implies the use of some such motive power or source of heat.
Obviously, however, there is no sharp line of demarcation between the
two. A lighted fire is strictly an artificial plan of ventilation, but
inasmuch as no apparatus intended for ventilating purposes is required,
it is hardly a means of artificial ventilation.

=Natural Ventilation.=—The most important means of natural ventilation
are the window and the chimney; but openings in outer walls and over
the door may form valuable adjuncts.

=The Window= is perhaps the most important agent in purifying a
room—both the light and air it admits being essential for health. The
window is invaluable (1) =for flushing the room= with fresh air at
intervals. Where possible, opposite windows should be opened, or window
and door. Cross-ventilation by opposite windows open at the top forms
one of the best means of natural ventilation, in large rooms, such as
school-rooms. This can, as a rule, be borne without discomfort, while
the room is occupied, unless the wind is very high.

(2) =The Upper Segment= of a window may be made to work inwards on a
hinge, and turned so that the current of air may be upwards. Where this
plan is adopted, triangular pieces of glass should be placed at the two
sides to prevent cold air from falling directly down at the sides of
the opening.

(3) =A Block of Wood=, two or three inches wide, may be inserted at
the bottom of the window sash at =A= (Fig. 12), and then the window
pulled down on this. The consequence is that air is admitted between
the two sashes at =B=, its current being necessarily directed upwards
(Fig. 12). This plan answers admirably in admitting pure air; but it
possesses a disadvantage common to all the plans in which external air
much colder than the internal is admitted into a room. The current of
cold air passes upwards for some distance, but may then fall down on
the heads of those occupying the room.

[Illustration: FIG. 12.


(4) The top sash of the window may be opened, and some =zinc gauze=
fastened across the open part. This is practically the same as the last
arrangement, except that the air is admitted through the apertures of
the zinc, and the amount admitted is greatly diminished (page 136).

(5) In =Louvre Ventilators=, a number of parallel pieces of glass,
each directed upwards, are substituted for a pane of glass. They may
be fixed or made movable, as in Moore’s ventilator. The incoming
current of air may be similarly directed upwards, in an open window, by
arranging Venetian blinds with the laths inclined upwards.

(6) In windows that will not open, =Cooper’s Ventilators= are often
used. Each of these consists of a circular disc of glass, having five
oval apertures in it, which works on a pivot through its centre, close
in front of one of the panes of a window, which has five similar holes
pierced in it. Consequently, when the disc is turned, so that its holes
are opposite those of the window, fresh air is admitted. The amount
thus admitted is necessarily small.

=The Chimney= forms the best means of escape of foul air. No room ought
to be built without a fire-place, which should never subsequently be
boarded up. In bedrooms the chimney forms a most important means of
ventilation. If there is no fire, the chimney occasionally furnishes
an undesirable source of air; but as a rule the current is upwards,
owing to the aspirating action of winds at the top of the chimney.
The downfall of air from a chimney chiefly occurs when there is an
insufficient inlet for pure air. This is the explanation of =smoky
chimneys= in nine cases out of ten; then the cure is easy by laying
on a pipe from the outside of the house to the hearth. When the smoky
chimney is due to the contiguity of higher buildings, the chimney must
be raised, or a cowl placed over it.

(1) The action of the chimney in carrying impure air away from the room
may be considerably increased by =narrowing the two ends=, so as to
produce a more rapid current at the entrance and exit of air.

(2) The heat of the chimney may be utilised by having a =separate
smaller flue= alongside it, with openings from the rooms on each floor.
The air in this being heated aspirates the air from each room in

Openings may be made into the chimney-flue at a higher point than
the fire-place. These are very valuable for carrying off the heated
and impure air resulting from the combustion of gas, as well as
for carrying off the respiratory products, which, in their warmed
condition, tend to rise towards the ceiling.

(3) =Dr. Neil Arnott= first devised a valve for this purpose. An
opening being made through the upper part of the wall into the chimney,
an iron box was inserted, in which was placed a light metal valve
capable of swinging towards the chimney flue, but not towards the room.
The objections to this apparatus are that it is apt to make irregular
clicking noises, and to admit blacks from the chimney when out of order.

(3) In =Boyle’s Valve= these objections are partially obviated. It
consists of an iron frame, across which lie iron rods; and from these
are suspended thin talc plates, only capable of moving in the direction
of the chimney (Fig. 13). Even this apparatus is rather noisy when
there is a strong wind.

[Illustration: View from room. View from chimney.

FIG. 13.


Neither of these plans answers so well as a second flue alongside the
chimney flue, communicating with each room near its ceiling; but the
latter can only be arranged for when the house is built, while the
valves may be inserted at any time.

=The Ceiling= may be utilised for removing foul air; and thus serve to
diminish the draught which is often produced by the currents of air
towards the chimney, when this forms the only means of outlet.

In large rooms (1) a sunlight gas-burner forms an important means of
ventilation. It causes a strong up-current from every part of the room.
If there is a fire in the room, the burner is apt to become an inlet
for air, or the chimney to smoke, according to the relative strength of
the two currents.

(2) Benham’s and other forms of =Ventilating Gas Burners= serve the
same purpose. In each of them the products of combustion are conveyed
by special ducts above the ceiling to the outer air.

(3) =McKinnell’s Ventilator= is useful in single-storied buildings,
like certain barracks. It consists of two tubes encircling one another,
the inner forming an outlet tube, because the casing of the outer tube
maintains the temperature of the air in it. It is made higher than the
outer tube, and is protected by a hood. The outer tube forms the inlet
for fresh air. The entering air is thrown up towards the ceiling and
then to the walls by a flange placed at the bottom of the inner tube.
The air after traversing the room, and becoming heated, passes upwards
to the inner tube. When doors and windows are open, both tubes become
outlets; if there is a fire in the room, they may both become inlets;
but this may be prevented by closing the outlet tube.

[Illustration: FIG. 14.


(4) Various other means have been devised for carrying foul air from
the ceiling through channels between the ceiling and the floor of the
room above. All share the disadvantage that the channels become dirty
and are difficult or impossible of access for cleaning.

(5) Various cowls connected by metal tubes with the ceilings of
rooms have been placed on roofs, and their aspirating effect
used in ventilating these rooms. When a room is furnished with a
chimney such cowls are most undesirable. In large rooms without a
fire-place they are helpful, but much more confidence can be placed
in cross-ventilation by hinged windows. It is doubtful if any of the
advertised fixed cowls produce materially greater aspiration of air
from rooms than a simple open tube of the same size. It is desirable
that the tube should be protected at its upper end against the entry of
rain, and that a grating should be provided to prevent birds building
their nests in the tube.

In the preceding plans of ventilation, the ceiling serves almost
entirely as an outlet for impure air. In the following plan, it is used
as an inlet for pure air.

(6) In =Sylvester’s Method of Ventilation=, the perflating force of the
wind is employed to produce an abundant entry of fresh air. A cowl is
placed, always turning towards the wind; the air received is conducted
to the basement, where it is warmed by a stove or hot-water pipes,
and then passed through tubes into the upper rooms. From these it is
carried by tubes above the roof, these tubes being covered with cowls
turning from the wind, so that in this way the aspirating power of the
wind is likewise used.

Ships are often ventilated in a somewhat similar manner. The tube to
which a windward cowl is attached above, ought to be bent at right
angles, so as to lessen the velocity of the entering air. By covering
other air-shafts with movable cowls, turning from the wind, the
aspirating action of the wind is brought into action to aid the escape
of foul air.

=The Walls= of a room, unless covered with an impervious material, are
constantly traversed by gentle currents of air, which play an important
part in the ventilation of rooms. Special apertures may be made to
furnish a freer supply, and these may be in various forms.

(1) =A Simple Grating=, may be inserted; but this is apt to become
blocked with dirt, and does not allow a large amount of air to enter.
Louvred openings in the walls are objectionable, except for very large

(2) =Sheringham’s Valve= is the most convenient means of ventilating
through the wall. An opening in the external wall is made by a
ventilating brick or grating; into the wall is fixed an iron box, which
has in front of it an iron valve hinged along its lower edge, so that
it can open towards the room. On the sides of the valve cheeks are
attached, which fit into the box when the valve is shut. A heavy piece
of iron pressing against the valve from within the box, tends to keep
it constantly open. By means of a string and pulley, the valve can be
opened or closed at will, or fixed in any intermediate position.

[Illustration: FIG 15.


In a very large room, it is better to have several medium-sized
valves, than a few larger ones, the air being thus more completely
diffused. If there are two valves, they should not be opposite one
another, as the air may then simply pass from one to the other, without
becoming diffused through the room. If there is only one valve, it may
occasionally serve as an outlet when the wind is to leeward. By means
of this form of valve, the air is projected upwards in a diverging
current towards the ceiling. The valve should be placed above the
level of one’s head, but not too near the ceiling; as in the latter
case, the current of air is driven hard against the ceiling, and
falls thence with considerable force towards the floor. A combination
of Sheringham’s inlet and Boyle’s mica outlet into the chimney at
the opposite side of the room ensures efficient ventilation in a
dining-room. Better than the outlet into the chimney is an opening into
a special flue alongside the chimney-flue, if this be available.

(4) =Ellison’s Inlet= consists of a brick pierced with conical holes,
the apex of the cone being towards the external air. By this means
any great draught is avoided, and the air is distributed over a
considerable area. In order that this may prove an efficient means of
ventilation, a considerable number of bricks are required.

The =Floor= of a room is always the source of considerable currents of
air, even when well carpeted. Air mounts up through the crevices of the
wood-work, being aspirated into the room when its temperature is higher
than that of the rooms below. In the case of rooms on the ground floor,
air is often drawn from the subjacent soil, or through dust-bins, etc.

Theoretically, in all measures of ventilation, the floor would be the
best point for the entry of cold air. This, however, is intolerable
when the incoming air is cold, and the floor must therefore be
abandoned as a means of ventilation, apart from heating apparatus.

The floor may be used as a means of entry of fresh air in a modified
manner, by directing the air entering at the floor-level for some
distance up a tube at the side of the wall. This apparatus is known
as =Tobin’s tube=. It consists of a rectangular or cylindrical tube
from 4 to 6 feet high, which communicates at the lowest point with the
external air by means of a perforated brick or grating. The air enters
the room in an upward direction, and is consequently sent towards the
ceiling, where it becomes mixed with warmer air, before diffusing
itself throughout the room. But when the incoming air is very cold, it
may fall more rapidly, causing cold draughts on the heads of those in
the room.

As the air enters directly from outside the house, it often carries
with it particles of dirt, soot, etc. This may be remedied by placing
a pan containing _a shallow layer of water_ at the lowest part of the
tube, or by placing _cotton wool_ at the point of entry of the tube
into the room. The tray of water soon dries up and is rarely replaced,
while the cotton wool diminishes the amount of entering air. It is very
useful however in cold weather, or when fogs occur. A _gauze funnel_ is
sometimes inserted in the tube, or a sheet of gauze arranged diagonally
across the tube from its highest to its lowest point. The gauze does
not keep out minuter particles of dust, and requires occasional
cleaning. All Tobin’s tubes, like other ventilating openings, should be
made to open, so that their interior can be frequently cleaned.

_Summary as to Domestic Ventilation._—Open windows, doors, and
fire-places may be in most instances trusted. If gas is used as an
illuminant, they should be combined with special arrangements for
carrying off the products of combustion from the room. For delicate
people, and especially in small rooms, outlet ventilation into the
chimney breast combined with a Sheringham’s valve on the opposite wall
is desirable.

=Artificial Ventilation.=—Artificial ventilation may include two
important and very different measures. In one of them currents of air
and an exchange of pure for impure air are effected by means of various
forms of heating apparatus. In the other mechanical measures are used
for the same purpose,—the air being either driven out of the room or
drawn out of it. In this chapter we shall consider only the =mechanical
means of artificial ventilation=. There are two kinds, the first being
known as ventilation by aspiration, or the _vacuum_ system; and the
second as ventilation by propulsion, or the _plenum_ system.

In =Ventilation by Aspiration= the foul air is drawn out of the room by
machinery, its place being supplied by fresh air, which may be warmed
before entry or not. This plan and the next have been employed chiefly
in connection with large buildings, such as hospitals, etc., and in

The extraction of foul air may be effected by—(1) _a steam-jet_, which
is allowed to pass into a chimney, and sets in motion a body of air
more than 200 times its own bulk. Tubes from each room of the building
are connected with this chimney, and the strong upward current extracts
the air from them. This plan is useful in factories, where there is a
superfluous supply of steam.

(2) _A fan or screw_ may also be used. The vanes of the fan, when set
in motion by electrical or some other motive power, produce a powerful
current of air, which can be regulated according to requirements. As in
the last plan, the aspirating influence of the fan may be exerted over
a system of rooms, by means of connecting tubes.

In =Ventilation by Propulsion= a fan is used as in the last plan, the
air being propelled along conduits leading from it into the room to
be ventilated. The size of the conduits being known, the amount of
air to be discharged can be regulated by timing the rapidity of the
revolutions of the fan.

This plan is suitable for crowded places, where a large amount of
air is required in a short time. It is excellent for large schools,
churches, and theatres. Its superiority for large elementary schools
has been proved at Dundee by the experiments of Drs. Carnelley,
Haldane, and Anderson, the results of which are summarised in the
following table:—

  Column headings:
  A  No. of Schools.   B  No. of Rooms.   C  Cubic ft. allowed per person.
  D  Carbonic acid in 10,000 of air.   E  Micro-organisms per litre.
  F  Bacteria.    G  Moulds.
  │                       │  A. │ B.   │   C.  │   D.   │      E.      │
  │                       │     │      │       │        ├────────┬─────┤
  │                       │     │      │       │        │   F.   │  G. │
  │_Mechanical ventilation│     │      │       │        │        │     │
  │   by warmed air_      │  6  │  32  │  160  │  12·3  │  17·5  │ 1·0 │
  │_Natural ventilation   │     │      │       │        │        │     │
  │   and hot pipes_      │  17 │  43  │  176  │  16·3  │  96·5  │ 1·1 │
  │_Natural ventilation   │     │      │       │        │        │     │
  │   and open fires_     │  33 │  84  │  145  │  19·2  │ 153·2  │ 4·8 │

The air to be admitted may be warmed by passing it over hot-water or
steam-pipes. In large establishments, as in hospitals, theatres, etc.,
it has been arranged so that the incoming air is passed through a
screen of coarse cloth, which is kept wet by water trickling down each
cord. The air is thus kept moist and freed from dust.

The great advantage of the plan of propulsion, is its certainty. By
it the temperature, moisture, and freedom from suspended matters of
the incoming air can be exactly regulated and controlled. Its chief
disadvantages are that (1) it is somewhat costly, and (2) the apparatus
requires skilled supervision. On the other hand it maintains the air
in crowded rooms in a condition which cannot be secured by any other
method. When combined, as is done in the Houses of Parliament, with
the use of a flue for the extraction of foul air, this plan answers

=The Relative Value of Artificial and Natural Ventilation= scarcely
needs to be discussed. They are both valuable, but under different
circumstances. In dwelling-rooms natural ventilation by doors, windows
and chimney usually suffices, especially if the products of combustion
of gas are removed through a special flue. Natural ventilation is
always occurring, and only needs a little aid in domestic life.
For large rooms occupied by many persons artificial ventilation is
necessary to maintain pure air.

Whatever method of ventilation is adopted, the atmosphere will remain
to some extent polluted, if the room and its occupants are dirty. In
certain experiments made by Carnelley in schools, it was found that
dirty children increased the number of micro-organisms per litre of air
more rapidly than dirty rooms. Thus:—

  │_Children_              │  63  │  99   │ 159  │
  │_Rooms_                 │  85  │  94   │ 139  │
                 _Number of micro-organisms per litre of air._

Hence cleanliness of rooms and of their occupants is quite as important
as a good system of ventilation.



=Ventilation by the Burning of Coal.= In winter and at any time of the
year when the out-door temperature is below 50° Fahr., the warming and
ventilation of a room are necessarily combined. If air is admitted
unwarmed it will produce draughts, unless directed upwards by Tobin’s
tubes or otherwise. In dwelling-rooms such contrivances may suffice;
but in any larger building, in order to ensure sufficient ventilation,
it is necessary to warm the incoming air.

=The Open Fire-place= forms the most common means of ventilation by
heat (see also page 159). The ascent of warm air up the chimney, causes
cold air to rush along the floor to the fire-place from all parts of
the room, especially the door. Part of the air thus approaching the
fire is carried up the chimney with the smoke, while the remainder,
after having been warmed, flows upwards towards the ceiling near
the chimney-breast. It passes along the ceiling, and cooling in its
progress towards the opposite wall, descends, and is again drawn
towards the fire-place. Thus there is a continuous circulation of the
air in a room.

In the experiments of the Barrack Commissioners (1861), it was found
that the amount of air passing up the chimney while a fire was lit,
ranged from 5,300 to 16,000 cubic feet per hour, the mean of 25
experiments being 9,904 cubic feet. We may conclude, then, that with
an ordinary grate, a chimney provides outlet for impure air sufficient
for four or five persons. Its lack of economy as a heat-producer will
be considered later. Its efficiency as a ventilator within the above
limits is evident.

When a fire is burning in the grate, all other openings in the room,
except openings into the chimney, serve as inlets. If the room is
insufficiently supplied with openings, a double current may be
established in the chimney, with the result that occasional down-puffs
of smoke occur.

As a rule the chimney serves only as an outlet for impure air. It
may by appropriate means be made to serve as an _inlet for pure and
warmed air_, the heat which would otherwise escape up the chimney being
utilised for this purpose. =Galton’s stove= is one of the best for this
purpose. At the back of this stove is an air-chamber, communicating
with the external air, and in which the fresh air is heated before
it enters the room. On the back of the stove broad iron flanges are
cast, in order to present as large a heating surface as possible. They
project backwards into the air chamber; and their heating surface is
aided by the iron smoke-flue, which passes through the air-chamber.
The warmed fresh air enters the room by a louvred opening above the
mantel-piece, or by an opening in each side of the chimney breast. By
this stove one-third of the total heat of the fire is utilised, as
against one-eighth in an ordinary fire-place.

[Illustration: FIG. 16.

Vertical Section through Two Rooms, showing—A. Currents of cold air
with an ordinary fire; B. Direction of currents of warmed fresh air
with a Galton’s Ventilating Stove.]

Shorland’s Manchester and other stoves are constructed on the same
principle as Galton’s.

 =The Ventilation of Mines= is effected by lighting a fire at the
 bottom of a shaft. The air for the combustion comes down another shaft
 (the intake shaft), or down another half of the same shaft separated
 by a partition. The consequence is that constant up and down currents
 of air are produced. The air from the intake shaft is made to traverse
 the galleries of the mines, its course being directed by partitions,
 before it is allowed to reach the fire and s be carried up out of the

In addition to, or instead of, an ordinary coal-fire, the power for
extracting impure air may be obtained from =Hot Water or Steam Pipes=.
There are various plans founded on this principle.

When hot-water pipes are used for baths, etc., they may also be
utilised for ventilation, in two ways:—1st. The hot-water pipe may
be made to coil round the tube by which fresh air is admitted into a
room, thus warming the air as it enters. 2nd. The hot-water pipe in
its course upwards may be enclosed in a shaft, which opens into the
external air above. The air in this shaft being heated, the impure
air may be collected and removed from the different rooms by tubes
connected with it. Thus, a hot-water apparatus, when well arranged and
complete, may furnish pure warm air, and carry away impure air. The
ventilation by this plan is found in practice to be somewhat irregular.

 The plan proposed by Drs. Drysdale and Hayward of Liverpool is similar
 in principle:—Fresh air is warmed by a coil of hot-water pipes in the
 basement, and is admitted into the staircase and landings, when it is
 supplied to the different rooms by openings provided with valves. From
 the rooms, special outlets converge to a foul-air chamber under the
 roof. This is connected with a shaft leading from the kitchen-fire,
 the latter, therefore, acting as an extraction furnace.

=Lighted Gas= may be employed to produce a current for ventilating
purposes, as well as fire or hot-water.

=Sunlight and Benham’s Ventilating Gas-burners=, have already been
mentioned in this connection (page 149). They are extremely valuable
means of ventilation, producing powerful currents of air from all
quarters of the room unless they are specially enclosed.

In theatres and similar buildings the =Chandeliers= may be made to
extract vitiated air. Where a number of chandeliers exist, they may be
connected by tubes with a main shaft, and all made to contribute to
the same object. According to the experiments of General Morin, the
discharge of 1,000 cubic feet of air is produced by the combustion of
one cubic foot of gas.

Various forms of gas-stoves are now sold, which act as ventilators as
well as sources of heat. Among these is =George’s Calorigen Stove=
(Fig. 17). It can be obtained in various forms suitable for burning
coal-gas, or coal, or oil. Within its outer case is contained a special
iron tube, which communicates at its lower end with the outer air,
and opens at its upper end into the room. The heat generated in the
stove warms the air in the spiral tube, which accordingly ascends
into the room. The ascent of warm air causes a draught from below,
and the consequence is, that so long as the combustion is going on, a
current of warm air continues to ascend into the room. The products of
combustion are carried out of the room by the pipe =F=. This stove is
free from most of the objections appertaining to gas-stoves; it can be
fixed into an ordinary fire-place, and made to keep the temperature of
a room uniform.

[Illustration: FIG 17.


 =A=—The interior of the room.

 =B=—Exterior of building.


 =D=—The Calorigen.

 =E=—A cylinder.

 =FF=—Pipes communicating with stove and cylinder to supply air for
 combustion, and to carry off the products of combustion.

 =G=—Pipe for passage of fresh cold air to Calorigen. Can be carried
 above the floor between the joists, as may be more convenient.

 =H=—Outlet for air into the apartment after being made warm.]

=Bond’s Euthermic Stove= is similarly constructed to the above, but
is open below so that the air needed for the gas combustion is drawn
from the interior of the room, and the continuous change of air is thus

=Objections to Ventilation by Heating Apparatus.=—When _warmed air_ is
admitted into a room, it is very apt to be _dry_ and irritating. This
can be usually avoided by having water standing in the room, so as to
allow evaporation. A more difficult problem is to ensure the complete
absence of all products of combustion, particularly of the products of
incomplete combustion.



=Physiological and Physical Considerations.=—The warmth of our bodies
is naturally kept up by the oxidation changes constantly going on
in the system. In Chapter XL., p. 265, are discussed the modes in
which heat is lost by the system, and the influence of clothing in
controlling the amount of this loss. Artificial warming of houses has a
similar action to clothing. It diminishes the demand on the system, and
so economises the amount of food required.

The degree to which this diminution of loss of heat by clothing and
artificial warming of houses may be carried varies with circumstances.
There can be no doubt that if food be abundant, exposure to external
cold, if not too extreme, is on the whole beneficial, for vigorous
people. But for old people and young children, means of artificial
warmth require to be more carefully provided. Severe cold is for them
often the harbinger of death.

The =Degree of Temperature= at which living-rooms should be kept will
vary with circumstances.

For _healthy adults_, any temperature between 50° and 60° Fahr., will
be moderately comfortable; for _delicate children and old people_ it
may be 65° with advantage.

For _sick rooms and hospitals_ the temperature of 60° is usually
adopted, but this is by no means always necessary. A temperature of
the room as low as 50°, except for such diseases as whooping cough and
bronchitis, suffices if the patient is well covered with warm personal
and bed coverings.

_Convalescents_ from any acute illness bear low temperatures badly.

=The Different Kinds of Heat.=—Heat may be communicated by radiation,
conduction, and convection. By =radiation of heat= is meant the process
by which heat passes from a fire or other source of heat, through a
vacuum, dry air or any other medium, without heating any of the media
through which it passes, but only the bodies against which it finally
impinges. The solid bodies (including ourselves) which are warmed by
radiant heat, by a process of conduction then warm the surrounding air.
This method is the nearest imitation of the natural warmth of the sun.

=Conduction of Heat= is the passage of heat from one particle to
another, whether it be of a gas or solid. It is an extremely slow
process when air is concerned, and may be practically ignored.

=Convection of Heat= is the process by which a gas or liquid actually
carries the heat in itself from one part to another. The heated
particles are relatively lighter, and ascend to the higher parts of a
room, while colder and heavier particles descend, and are subjected
to the same process. Heat can be carried by convection only by gases
and liquids. It is quite possible, therefore, for a person to be cold
in a room filled with warm air, if the walls, etc., are cold; and on
the other hand, to feel comparatively warm in a room filled with cold
air, if more heat is radiated from an open fire-place or the warm
walls to his body than he radiates to his surroundings. The feeling of
“draught” when sitting near a wall is sometimes caused by radiation of
heat from the body to the colder wall. The ideal arrangement, were it
practicable, would be to have cool air to breathe, but to be surrounded
by warm walls, floors, and furniture. A room warmed by an open fire
is more comfortable than a room warmed by hot air from a furnace,
assuming the temperature of the air is the same in both instances,
because the walls of the room are several degrees lower in temperature
in the latter than in the former. For warming walls as well as the air
high pressure steam pipes are more efficient than hot-water pipes. The
great advantages of radiant heat are that—(1) it heats the body without
appreciably heating the air; while at the same time (2) there is no
possibility of impure gases being added to the air.

It has, however, considerable disadvantages. (1) It is costly, though
its expense may be greatly diminished by a well-constructed fire-place.
(2) It only acts on bodies near it to any useful extent. Its effect
lessens as the square of the distance; thus, its warming effect at
five feet distance, is twenty-five times less than at a distance of
one foot. It is evident, therefore, that for long rooms, and for large
assembly-rooms, a single source of radiant heat is quite inadequate.
The immense loss of heat in our ordinary fire-places is slowly leading
to their modification; and although it is probable that radiant heat
will always be the favourite source of warmth in dwelling-houses, it
will be used for larger buildings chiefly as an adjunct to convection
of heat.

The different sources of heat are employed, either singly or combined,
in the following methods of warming our dwellings and other buildings:—

  1. Warming by the open grate.
  2. Warming by closed stoves.
  3. Warming by hot-water pipes.
  4. Warming by steam in pipes.
  5. Warming by hot air.
  6. Warming by electricity.

=Warming by the open Grate.=—In the open fire-place radiation is the
source of heat chiefly employed.

The =position of the fire-place= is important. It should not be on the
external wall of the house, as thus a large proportion of heat is lost;
but should be placed where the heat from the flue may be utilised in
keeping up the temperature of the house.

The =construction= of a fire-place is commonly faulty in several
respects. (1) The fire-place may be too far included in the wall, so
that the heat at once passes up the chimney. (2) It may be composed
chiefly of iron, which rapidly conducts away the heat, and does not
furnish a surface for radiation. (3) The bars and bottom of the grate
may be so arranged, that coal and cinders fall out in an incompletely
burnt condition.

It has been estimated that with an ordinary fire-place, seven-eighths
of the possible heat is lost, one-half being carried up the chimney
with the smoke, one-quarter carried off in the ascending current
of warm air, and one-eighth of the combustible matter remaining
unconsumed, forming the solid matter of the smoke.

The defects which have been indicated may be remedied by bringing the
fire-place rather further out into the room; by substituting fire-brick
for iron behind and at the sides of the fire, and by having a layer of
fire-brick at the bottom of the grate, or the grate lowered, so that as
in Teale’s stove, it lies on a bed of fire-brick at or below the floor

The =shape of the grate= is important. The width of the back of the
grate should be about one-third that of the front, the sides sloping
out towards the front of the recess. The depth of the grate from before
backwards should be equal to the width of the back. The sides and back
of the fire-place must be made of fire-brick, thus ensuring the heat
being retained in the grate. And finally, the chimney throat must
be contracted so as to ensure more complete combustion. The =chief
objections to an open fire-place= are (1) the great waste of fuel
involved, even after the improvements indicated have been carried out.
(2) The unequal heating at different distances from the fire. (3) The
smoke and dust always produced to some extent, from accidental smoking
of the fire, or from the escape of ashes. (4) The trouble involved in
frequently replenishing the fire. (5) The cold draughts produced by the
currents of air towards the chimney. These travel chiefly along the
floor, when, as is commonly the case, the space between the bottom of
the door and the floor forms the chief place for the entry of fresh air.

Many patents have been brought out for the =introduction of the
fuel at the lowest part= of the fire. The uppermost part of the
fuel being first burnt, and the remainder attacked from above, the
smoke is consumed in passing through the red part of the fire. Thus
a comparatively smokeless fire is produced, and the amount of heat
evolved is greatly increased. So far none of these have been altogether
satisfactory. The production of _a comparatively smokeless fire_ is a
great boon. =Smoke= means so much unburnt fuel, and not only so but the
sooty particles float about in the atmosphere, rendering it impure, and
changing comparatively harmless mists into town fogs, which are loaded
with soot and the products of combustion, and do incalculable mischief
to health and property. The prevention of this =smoke nuisance=
demands more consideration than it has yet received. The Public
Health Acts constitute the emission of black smoke from the chimneys
of manufacturing premises a nuisance; and manufacturers can if they
use proper boilers, especially those in which mechanical stokers are
employed, almost completely obviate this nuisance. The great principle
is to prevent the escape of smoke before it is completely burnt. This
may be accomplished by careful stoking, by keeping the unburnt coal
at the front of the fire, and by ridges exposing the smoke to red-hot
fire-clay before it escapes. In domestic fires, gas is gradually
replacing coal for cooking, with a corresponding reduction of the

=The Utilization of the Heat Produced= in the fire-place to warm the
air on its way into the room, as in Galton’s and other similar stoves
has been already described (page 156).

A larger amount of heat can be obtained out of a given quantity of fuel
by cutting off some of the cold air, which rushes through the fire, and
carries the half-burnt gases and much of the heat up the chimney. This
is effected by having a solid fire-brick bottom to the grate, or by
closing up the front of the open chamber under the grate, by means of a
close-fitting shield or door. These “Economisers,” as Mr. Teale calls
them, appear to answer better than solid fire-brick bottoms, as they do
not prevent the ashes falling under the grate.

=The Fuel= burnt in an open fire-place may be either coal or coal-gas.
Occasionally coke is also employed. Coke and coal-gas have the
advantage over coal, that (1) no smoke is produced. Coal-gas presents
the additional advantages, that (2) it can be turned on at any moment,
without having to go through a tedious process of lighting the fire;
and that (3) the amount of heat can be exactly graduated by regulating
the supply of gas. A gas fire is however, as a rule, more expensive
than a coal fire.

=Open Gas-stoves= are made in various forms. In the common one, small
jets of gas are lit under the grate, which is filled with pieces of
asbestos. These become red hot, and radiant heat is emitted. To obtain
the greatest value from the heat generated by the combustion of gas,
a stove should be chosen in which the heat generated is brought into
contact with a large surface of the grate before the products of
combustion are allowed to escape to the flue.

Gas stoves which are advertised as not needing a flue, should be
avoided. A large amount of carbonic acid is discharged by them into the
room, and the sulphurous acid also produced by the combustion of gas is
not completely absorbed in the water of condensation which collects in
a tray under such stoves.

=Closed Stoves= form the most economical and efficient warmers for
rooms of moderate size, and coal, coke, coal-gas or paraffin may be
burnt in them.

_The advantages_ rightly claimed for coal stoves of this type are that
(1) the amount of fuel consumed is small; (2) by adjusting the damper,
combustion may be rendered as slow as desired, so that but little
heat is lost by the flue or chimney; and (3) heat radiates from all
parts of the stove into the room, and not simply from a small area of

_The chief objections_ to closed stoves are, that (1) they _dry_ the
air excessively, rendering it somewhat unpleasant. (2) They produce a
peculiar _close smell_, apparently caused by the charring of minute
particles of organic matter in the air, coming in contact with the
stove. If the air of the room is not heated above 75° Fahr., no
smell is produced, and the relative humidity is not lessened to any
appreciable extent (Parkes). But when the heat produced by the stove is
excessive, these results do follow. The unpleasantness may be modified
though not entirely removed, by placing shallow pans of water near the

(3) Portions of the _products of combustion_ may pass through cracks
or fissures in the stove, or even through the joints of the stove.
Independently of such accidental cracks, cast-iron stoves, when red
hot, appear to allow gases to pass through them with comparative ease.
Thus carbonic oxide and other gases may find their way into the room,
and it is probable that this rather than the dryness of the air, is the
cause of the unpleasant symptoms sometimes complained of in rooms where
closed stoves are in use. This escape of carbonic oxide does not occur
with earthenware stoves properly encased with fire-clay.

Many modifications of the older closed stoves are now in common use. In
the stove shown in Fig. 18, excessive heating of the air is prevented
by the presence of two air chambers, only the outer one, which brings
external air to be warmed, having its air emptied into the room.

[Illustration: FIG. 18.


Warming by open grates or closed stoves is specially applicable to the
rooms of private houses; warming by hot air or steam, or hot water,
is chiefly used for large buildings. It is quite possible that these
methods will be applied at some future time on a large scale to the
warming of private houses. In some large towns of the United States
this has been already done, blocks of a hundred or more houses being
warmed from the same centre, by the same system.

But apart from such a central system, hot air and hot water lend
themselves to the heating of houses on what may be called the _Whole
House System_ (page 156). We have mentioned in the last chapter some
methods of doing this, and shall now describe others.

=Hot-water Pipes= are probably the best means of carrying heat to
various parts of a large house, and hot water is more thoroughly under
control and less dangerous than either hot air or steam. There are _two
systems_ of heating by hot water.

In the first, which we may call the =low pressure system=, there is
a boiler from which water circulates through pipes to every part of
the building, and as it cools down returns again to the boiler. At
the highest points of the pipes, outlets are provided for air. In
this system the water is not heated above 200° Fahr., and there is
consequently no great pressure on the pipes.

In the =high pressure system= (Perkin’s patent), the pipes have an
internal diameter of about 1∕2 an inch, and have thick walls made of
two pieces of welded iron. There is no boiler, but one portion of the
tube passes through the fire and the water is heated to 300-350° Fahr.,
thus subjecting the pipes to great pressure. In dwelling-houses with
the low pressure system, for every 1,000 cubic feet of space to be
warmed to 50°, 12 feet of 4-inch pipe should be given; with Perkin’s
pipes, probably about two-thirds of this will suffice.

=Steam Distributed by Pipes= may be employed instead of hot water. This
method has been used in factories in which there is a surplus supply of

=Warming by Hot Air= is only applicable on a large scale, and should
only be used in association with a system of ventilation by propulsion
(page 153), in which the temperature, humidity, and freedom from dust
of the entering air are carefully regulated.

=Warming by Electricity= both for cooking food and for warming rooms
has a large future, but in most districts the supply of electricity is
not hitherto sufficiently cheap to be used for these purposes. By its
means the atmosphere will be prevented from becoming impure, labour
will be reduced, and life rendered more pleasant.

=Hot Water Supplies.=—Nearly every modern house is supplied with
a bathroom, and this may be supplied with hot water either from a
geyser or from the kitchen boiler. In a _geyser_ the water is made
to flow over a large heating surface furnished by burning coal-gas,
and with the best varieties a bath of 98° F. can be supplied in from
five to ten minutes. As the bathroom is usually small and unprovided
with an open fire-place, persons have occasionally been suffocated by
remaining in such a room while the gas continues burning. This is due
to the production and in-breathing of carbonic oxide. No geyser ought
to be allowed to be used which is unprovided with a flue passing into
the chimney flue or in its absence through an external wall of the
house. Short of fatal poisoning, violent headaches often occur when
a warm bath obtained by means of a geyser is taken, unless such a
flue is provided. In Ewart’s lightning geyser, additional protection
is furnished by the fact that a dual valve is so arranged, that
immediately the water is turned off or the supply fails from any cause,
the supply of gas is also cut off.

Hot water supplies from =kitchen boilers=, unless carefully arranged,
may be responsible for serious explosions during severe frosts.

 Four plans are in common use. (1) _The worm-boiler system._ This
 system is unsafe unless the supply of water to the boiler is attended
 to; and as the hot water supply to the kitchen is drawn from the
 boiler itself and not from the worm, the hot water supply for the rest
 of the house may be deficient. Usually the small feed cistern for the
 boiler in this system is too near the boiler to freeze.

 (2) _The cylinder system_ is very effective. In this system a metallic
 cylinder, capable of withstanding a pressure of 20 lbs. to the square
 inch, is placed in the kitchen or bathroom between the cold and hot
 supplies, its contained water being heated by circulation from the
 boiler, hot water ascending and cold descending. On the top floor of a
 house is a cistern from which cold water is supplied. Both the supply
 pipe and escape pipe for hot water may become frozen during frost.
 Then the supply of water is stopped, and the boiler and reservoir may
 boil dry. This would not occur without some indication in unusually
 vigorous boiling. Boilers sometimes explode, and cylinders sometimes
 explode. This can be effectually prevented by (3) _A Double-cylinder
 apparatus_ one within another. In this the water in the outer cylinder
 supplied from the main cistern can only be heated to 212° F., and the
 water in the boiler and inner cylinder supplied from a lower feed
 cistern can only be heated to 214° F., on account of the small head of
 water. Two escape pipes give free communication with the atmosphere.
 (4) In the _tank system_, which being cheap, is usually adopted in
 poor houses, the tank is placed high up in the system. The hot water
 branch pipes are usually taken from the flow-pipe between the boiler
 and tank. Hence when the supply fails, as during frost, the tank is
 drained empty, the circulation of water ceases, and the system is
 changed from a circulation system to a high-pressure one.

 Safety valves cannot always be relied on to prevent explosions. If
 they lead to the lighting of fires in frosty weather, when pipes are
 frozen, they may cause explosions. Explosions from frost only occur
 when both pipes are blocked. Incrustation of the boiler and pipes
 increases the danger of explosions; hence the necessity for their
 periodical cleaning.

[Illustration: Cylinder and Tank systems]



=The Removal of Impurities.=—In order that health may be maintained in
any inhabited house, it is essential that the impurities produced by
animal life should be removed. These impurities may be divided into two
classes—the first including the gaseous and volatile products evolved
from the lungs and skin; and the second, the liquid excretion from the
kidneys, and the solid from the bowels. The former are got rid of by
efficient ventilation and by cleanliness; the latter, ought to be as
quickly removed, but require more elaborate arrangements to ensure this.

The =average daily amount= of solid excreta is about 4 ounces, and of
fluid excreta about 50 ounces for each adult male. Taking all ages
and both sexes into consideration, the amount per head is about 2-3∕4
ounces of fæces and 32 ounces of urine. When dried, the daily fæces
amount to 1·04 oz., the daily urine to 1·74 oz., so that the manurial
value as well as the possible polluting power of urine is much greater
than that of the fæces.

After a variable interval urine and fæces begin to decompose, ammonia
and fœtid gases being disengaged in large quantities. Urea the chief
constituent of urine is decomposed into carbonic acid and carbonate of
ammonia. Thus

  CH₄N₂O + 2H₂O = (NH₄)₂CO₃

In addition to the excreta, house-slops have to be got rid of, and
“dust.” =House-slops= vary greatly in quantity, but probably amount to
as much as sixteen gallons per head daily. They consist chiefly of the
water used in cooking and washing and for baths. It would be a mistake
to suppose that only urine and fæces need careful disposal. There
are masses of decaying epithelium from lavatories and baths, organic
matters from soiled apparel, and various organic matters from culinary
operations, all of which may cause serious nuisance unless promptly
disposed of.

The =Dust= consists chiefly of the ashes from fires; but the dust-bin
also forms a favourite refuge for kitchen refuse, composed of various
animal and vegetable matters, as well as for broken pots and tins. It
is dealt with apart from the house-slops and excreta, except in certain
dry methods of disposal of sewage.

Two chief plans of getting rid of the sewage have been proposed, though
there are many varieties of these. They are—

  1. The Water Method, and
  2. The Dry Methods.

For towns the water carriage of sewage is indispensable, and in this
chapter we shall confine ourselves to the part of this system which
relates to the =Drainage of the House=.

The chief sanitary appliances of a house, which empty their contents
into the drain and thence into the street sewer, are—(1) Rain-water
Pipes; (2) Bath-room and Sink-pipes; (3) Water-closets; (4) Soil-pipes;
and (5) The House Drain. We will consider these in detail.

=Rain-water Pipes= collect the water from the roof by means of gutters,
and carry it down to the house drain, except in the few cases in which
the rain-water is collected for use. The rain-water or stack pipe was
formerly joined directly at its base with the underground drain. This
was evidently bad, because the upper end of the pipe was frequently
near windows, and foul gases from the drain might be conducted by it
into the house. It is equally objectionable to connect the rain-water
pipe with the soil pipe and for the same reasons as above.

_The general rule with regard to all pipes carrying away water from the
house, with the sole exception of the soil-pipe, is that they must be
disconnected from the underground drain and discharge into the open air
over a gulley-trap._ This rule applies to

  rain-water pipes, and to
  waste pipes from baths,

  It does not apply to the soil-pipes leading from
                                     water-closets and
  which must discharge directly into the drain.

Overflow or waste-pipes from cisterns for drinking water or from
cisterns for flushing w.c.’s or to safe trays under the seat of
water-closets should all be made to discharge into the open air, where
the leakage can at once be discovered.

The form of gully-trap to be used at the junction with the drain is
described on page 167.

=Other Waste-pipes= as from bath, lavatories, and sinks, must be
similarly disconnected from the drain, and made to discharge over
gully-traps. When the pipe leading from the bath, lavatory basin, or
sink, is long, it is apt to become foul from the accumulation on its
inner surface of slimy matter, consisting of soap, dirt, and other
offensive matter. For this reason it is wise to have a syphon bend in
the waste-pipe near its junction with the sink or basin. Such a trap is
shown in Fig. 19.

The syphon bend alone in the waste-pipe without disconnection from the
drain at its lower end would not suffice to ensure complete absence
of nuisance, especially for sinks and lavatories which may be disused
for a considerable period. Under these circumstances the water in
the syphon trap may become evaporated, and then foul drain gases be
wafted into the house. Furthermore, even if the water in the syphon
trap remained, foul gases may be absorbed from the drain and given out
at the end nearest the house (_a_, Fig 19). Hence it is always best
to disconnect all waste-pipes from the drain, except the soil-pipe
which cannot be treated in this way. The waste-pipe from the upstairs
lavatory or bath may be made to discharge over a hopper-head and thence
into the rain-water pipe, which is disconnected below from the drain.
This plan should only be adopted when the hopper-head is not close to a
bedroom window.

[Illustration: FIG. 19.


Under the bath is usually placed a leaden tray, called a _safe_, to
catch any accidental spillings of water. The overflow pipe from this
safe should discharge direct into the open air. Formerly much evil was
caused by allowing waste-pipes from baths, sinks, and lavatory-pipes,
or overflow pipes from drinking-water cisterns or from the bath-safe,
to be connected directly either with the trap of the w.c., or with the
soil-pipe beyond it.

[Illustration: FIG. 20.



=Sinks= are not uncommonly the source of offensive smells, when made
of wood or stone. A hard glazed sink should be provided; as this is
non-porous and can be kept clean. The sink should be placed against an
external wall, so that the waste pipe can be carried through the wall
to a gully-trap outside the house. Formerly the sink-pipe was joined
below directly into the drain, the only obstacle to the entry of sewer
or drain gases into the kitchen being a bell-trap at the sink. This is
quite insufficient for the purpose. The waste-pipe from the sink should
have a syphon trap under it, with an inspection opening at its lowest
point (Fig. 19), and should discharge in the open air over a gully-trap
(Fig. 20), as in the case of rain-water and bath-waste pipes. It is
usually stated that the waste-pipes from sinks, etc., should discharge
at least 18 inches distant from the grating of the gully. This is
too far, because some of the foul water may become dried up in the
channel, and its solid particles be blown about. They may be allowed to
discharge directly over the grating of the gully (Fig. 20) or even into
the side of the gully below the grating, but above and on the house
side of the water-seal shown at B. Fig. 20.

The gully-trap is connected with the socket of the first drain-pipe,
and the junction is made water-tight by means of a cement joint.
On this account, and because it gives a better water-seal than the
bell-trap or D trap, the gully-trap should be always used. The best
form of gully-trap, the P trap, is shown in Fig. 20 B. This is better
than the S trap (Fig 19), which involves a bend in the drain at its
junction with the trap.

=Water-closets= require to be skilfully constructed and well-situated,
if they are not to become a serious nuisance. In building a house, the
_position_ of the closet should be carefully considered. In all cases
it should be in an out-standing part of the house, against an external
wall, and separated from other parts of the house by a passage,
preferably a passage which is cross-ventilated. Instead of this, one
commonly finds it in any convenient recess, abutting on a bedroom, or
where it cannot be properly ventilated. Usually the closet is placed
at the back of the house; and as the main-sewer is generally situated
in the front street, it follows that the drain must in terrace houses
pass under the house. Hence the importance of having it completely
water-tight. Water-closets in bathrooms are very inadvisable.

The _ventilation_ of the closet should be good—if possible, by two
opposite windows; and where practicable a cross-ventilated lobby should
intervene between the closet and the rest of the house. This is now
always provided in hospitals.

The _water-supply_ to the closet should be abundant. Every flush of
water should be sufficient to carry the contents of the basin through
the soil-pipe and the drain into the sewer. The quantity allowed by the
Water Companies in London is two gallons, which is barely sufficient
for this purpose, unless the form of closet pan is good, and the
down-pipe to it of sufficient diameter. Each closet should have a
separate cistern, the best being the so-called “water-waste preventer,”
by means of which a certain quantity of water, and no more, can be
discharged each time the handle is pulled. One of the best of these is
shown in Fig 21. When the handle of this is pulled, the whole of the
water in the cistern is syphoned out by the syphon and carried down to
the water-closet, whether the handle be held down or not.

The amount of fall from the cistern to the closet should not be less
than four feet, and the pipe should be free from bends in order
to ensure a thorough scouring of the trap and soil-pipe; and the
flushing-pipe should have an internal diameter of not less than 1½
inches. It is commonly supposed that a small flow of water, trickling
continuously down a closet, tends to keep it clean, and prevent
smells; but the water thus used is simply wasted. Others fasten up the
handle of valve-closets so as to allow a large flow of water. This does
not answer the desired end, and renders the offending person liable to
a penalty for wasting water.

Many different forms of water-closet are in use. In all of them the
main requisites are that there should be (1) a good flush of water, (2)
a rapid removal of the excreta, and (3) no possibility of reflux of
gases. The chief varieties of closets are the pan, valve, wash-out, and
wash-down closets.

[Illustration: FIG. 21.


 In Fig. 21 a portion of the bell of the syphon is shown cut out,
 so as to display the movable plug at the bottom of the cistern. An
 objectionable feature in most cisterns is their noisiness in use. In
 the above cistern, the pipe admitting water is carried down to within
 an inch of the bottom of the cistern, thus ensuring noiseless entry of

=Pan-closets= (sometimes called _double-pan closets_) are essentially
bad, though largely employed in the past. The construction is shown in
Fig 22. Below the conical basin there is a metal pan capable of holding
a certain amount of water, the lower end of the basin dipping into
this water. By means of a pull-up apparatus the contents of the pan
can be tilted into a second larger pan or _container_, and the bottom
of the container is connected by means of a short pipe with a leaden
[bowl-shaped symbol] shaped trap, from the side of which the soil-pipe
passes out to be carried down to the drain. The arrangement insures the
production of nuisance. The container and [bowl-shaped symbol] trap
always arrest a certain amount of foul matter; and each time the handle
of the closet is pulled up a puff of foul air comes into the operator’s
face. Occasionally the [bowl-shaped symbol trap becomes corroded by the
filth it contains, and foul gases from the drain escape into the house.


=Valve Closets= differ from the last in having no container, but only
a small box containing a movable water-tight valve, exactly fitting
the lower edge of the basin (Fig. 23). They are much superior to the
pan-closet, but require an overflow pipe in order to avoid accidental
flooding of the closet. The overflow pipe should be made with a syphon
bend in it, and the flushing of the closet should be so arranged that
each time it is performed water enters the overflow pipe. (See Fig.
23.) The trap below the valve should be in the form of a syphon (see
under traps, page 179), as this is not easily fouled. It is preferably
made of lead, securely jointed to the soil-pipe and to the valve box
of the closet. A lead tray or “safe” is required on the floor beneath
a valve closet, in view of accidental spillings or overflow; and this
should be provided with an overflow pipe discharging into the open air.

[Illustration: FIG. 23.


=A—Pan=. =B=—Overflow pipe with syphon trap. =C=—Valve shut.
=C₁=—Valve open. =D=—Valve box. =E=—Floorline. =F=—Water-seal of trap.]

=Valveless or Hopper Closets=, of which the =Wash-out, Wash-down and
Syphonic Closets=, are the chief forms, present certain advantages over
the valve closet. There is less apparatus to get out of order and no
metal to become foul. They do not require an overflow pipe, as water
can escape freely through the trap of the closet. Valveless closets
need not be encased by wood-work, thus ensuring freedom from spillings
of foul water, and they are more easily used than valve closets for the
discharge of bedroom slops, thus obviating the necessity for a special
housemaid’s sink. Valveless or hopper closets are cheaper and simpler
in use than valve closets, and when in use are equally sanitary. If a
house is left empty for a considerable time, the water in the trap may,
however, become evaporated, an event much less likely to occur with a
valve-closet. The latter are furthermore less noisy when flushed. With
a valve to hold up the water in the pan, as in the valve-closet, a much
larger quantity of water can be retained than with a hopper closet.
Hence the importance of the latter having such a shape as shall prevent
fouling of the basin by fæces.

One of the older hopper closets was the =long hopper= shewn in Fig.
25. In this form the pan is conical in shape, its sides necessarily
becoming fouled by its use, and the spiral flush, the point of entry of
which is shewn in the figure is quite insufficient for cleansing the

Of =Short hoppers= the best has a nearly vertical back as shewn in Fig.
24, a rim-flush, by means of which at least two gallons of water are
discharged with the fæces, and the pan is thoroughly cleansed.

[Illustration: FIG. 24.


The =wash-out closet= is shewn in Fig. 26. In it a certain amount of
water is kept in the upper part of the pan by a ridge over which the
fæces have to be driven before entering the trap. The force of the
flush is thus broken. In this closet a large area is liable to be
fouled, and it is now almost entirely disused.

[Illustration: FIG. 25.


=Syphonic water-closets= are wash-down closets, in which the flushing
out is aided by syphonic action. They need to be fitted with a flushing
cistern, giving an after-flush as well as a flush; otherwise the basin
is left untrapped. One of the most elaborate closets of this type
is Jennings’ Closet of the Century. Fig. 27 shows that the flushing
cistern has two connections with the closet, one in the usual manner
with the flushing rim of the pan, the other connected to the long arm
of the syphon (A Fig. 27). B is a puff pipe allowing the escape of air
from this syphon when started. Thus while one part of the flush scours
the basin, the other expels the air from A through the puff-pipe B,
fills both arms of the syphon with water, and thus starts the syphonic
action by which all the contents of the basin are sucked out of it.
In this form of w.c., syphonage is intended to be produced, and the
after-flush prevents the w.c. from being left untrapped.

[Illustration: FIG. 26.


[Illustration: FIG. 27.


Syphonic water-closets appear to me to be unnecessarily elaborate and
complicated, and the only advantage over the wash-down closet is the
deeper layer of water in the basin. With a well-shaped wash-down closet
this is of little importance.

In other forms of wash-down w.c., =unsyphoning= may also occur, for
instance, by pouring the contents of a slop-pail into the pan. This
is particularly apt to occur, when two or three water-closets are
on different floors of a house, one over another. This unsyphoning is
prevented in the case of the highest w.c. by the soil-pipe ventilator,
but not always for the lower w.c.’s. For these it may be necessary to
carry a pipe from the highest point of the trap of the closet, where
it joins the soil-pipe, through the wall into the external air. Such
a pipe is called an _anti-syphonage pipe_ (Fig. 28). It effectually
prevents the water being sucked out of the trap of a lower w.c. when
the w.c. on a higher floor is being flushed.

[Illustration: FIG. 28.

 A—Elevation. B—Section through wall of house, showing connection
 of w.c.’s on three floors, with soil-pipe and anti-syphonage pipe.
 _b_—Junction of closet trap with soil-pipe, _a_ being a P and
 _b_ an S trap. _c_—Junction of soil-pipe with earthenware drain.
 _d_—Anti-syphonage pipe, seen best in elevation A. _e_—Soil-pipe.
 _f_—Anti-syphonage pipe. _g_—Underground drain. _h_—Soil-pipe
 ventilator. _i_—Cage-work protecting top of _h_. _j_—Point at which
 anti-syphonage pipe is connected with soil-pipe ventilator, above the
 highest w.c.]

In the forms of w.c. already described, clean water is used for
flushing, and we have seen that two gallons, the quantity usually
allowed, does not suffice for this purpose, unless the closet pan is
of the best possible shape, and the service pipe sufficiently wide to
project the water by means of a rim-flush forcibly over the pan and
into and beyond its trap. Other forms of w.c. have been employed of
which the most important are slop-water closets, and trough-closets.

In =Slop-Water Closets= the waste water from sinks and baths is
utilised for flushing, and thus a saving of water is effected. This
form of closet is used considerably in manufacturing districts, and is
less liable to freeze than an ordinary w.c. The sink discharges on to
a gully in the usual manner, but the outlet of this gully is connected
with a tilting vessel or tipper, holding 3½ gallons in Duckett’s
closet, which is the best known of this type. The tipper is balanced
on brass bearings, and tips over when full, discharging its contents
into the closet trap, which is thus flushed. The slop-closet is a great
improvement on the privy-middens or pail-closets, which in some towns
it has superseded, but is not so cleanly as an ordinary w.c.

=Trough Closets= are also known as “latrines.” The best type consists
of a glazed earthenware trough under a series of w.c. seats. The trough
is slightly inclined towards the outlet, at which is a weir, beyond
which is a trap. An automatic flushing tank connected with the upper
end of the trough and five to six feet above it, discharges water at
intervals and drives the fæcal matter over the weir and through the
trap. This form of closet is only suitable for factories. It is to
be deprecated for schools, and even for factories, unless there are
exceptional reasons for its continuance, as fæcal matter possibly of an
infectious character may be retained a considerable time in the trough.

The domestic =Slop Closet= or “housemaid’s sink” must not be confused
with slop-water closets mentioned above. The slop-closet or sink
is used for emptying the contents of bedroom pails. These being
necessarily foul and liable to early putrefaction must be treated
exactly like other sewage matters. An ordinary pedestal w.c. with
a lift-up seat answers excellently as a slop-closet; but in large
houses and public establishments a separate slop-sink is desirable
with a larger surface than most water-closets. The slop-closet must be
connected with the soil-pipe, just in the same way as a w.c.


 _A._—Sewer; _B._—Intercepting trap; _C._—Cleaning eye for pipes
 between chamber and sewer; _D._—Inspection chamber; _E._—Inlet
 ventilator; _F._—Gully-trap for forecourt; _G._—Air-bricks
 for ventilation under floors; _H._—Damp-proof course[8];
 _I._—Concrete 6” thick over site of house; _J._—Drain, fall 1 in
 24, imbedded in concrete; _K._—Soil-pipe carried up full size
 above eaves; _L._—Upstairs w.c.; _M._—Gully-trap receiving water
 from _N_ scullery-sink, _O_ bath and _P_ rain-water stack-pipe;
 _S._—Ventilating pipe at upper end of drain; _T._—Pipes leading to

] =The soil pipe= is the vertical pipe carrying the contents of the
water-closets in the drain. It must be distinguished from the drain,
which is chiefly, if not entirely, underground. The exact position of
the soil-pipe and its relation to the drain can be seen in Fig. 28 and
29, which should be carefully studied. The soil-pipe should be made
of drawn lead without seam, of uniform thickness throughout, and of at
least 7 lbs. or better 8 lbs. weight per superficial foot. Any joints
in the lead pipe should be of the kind known as “wiped,” not a “slip”
joint. The outside of a wiped joint is shewn in Fig. 30B. Iron pipes if
used must be 3∕16 inch thick, and have sockets sufficiently wide and
strong to permit of the joints being caulked with molten _i.e._ “blue”
lead, in the same way as water-mains are laid.

The soil-pipe should be throughout its course under observation. It
should not be built into a wall, where it might be accidentally pierced
by nails, nor within the house, allowing foul gases to escape from weak
points in the joints. It should be carried through the wall of the
house immediately beyond the closet trap.

The soil-pipe should not be more than four inches in diameter. It
should be continued from its highest point at the junction with the
closet-trap above the roof by a pipe of the same diameter, with its
end wide open (Fig. 29 K). This _ventilation of the soil-pipe_ is
essential (_a_) to prevent the entry of foul effluvia into the house,
especially when the water in the closet-trap is dried up; (_b_) to
prevent unsyphoning of the upper by the lower water-closets in a house.
(On this point see p. 172).

[Illustration: FIG. 30.



The upper end of the ventilating pipe should be made to open remote
from any window. It may have a cowl attached to it, but it is doubtful
if this materially aids the aspiration of foul gases. It is wise to
cap the upper end of the ventilating shaft with a dome of large meshed
wire-netting to prevent birds building their nests in it.

The connection of the soil-pipe with the closet-pan is its weakest
point, and the most liable to leak. The main difficulty consists in
forming =joints between earthenware and metal=. Socketed connections
are not safe. The use of an india-rubber ring inserted between the
lead and earthenware flanges and bolted together by means of a brass
collar and hooked bolts makes a fairly good connection. Various screwed
connections are made. In another form the earthenware collar is covered
outside with lead, so that a soldered joint can be made between the
earthenware trap and the soil-pipe. In the “metallo-keramic joint”
the earthenware joint is painted over with a metallic solution and
fired. To the metal film thus formed, lead or other metal can be firmly

The connection of the soil-pipe into the socket of the first pipe of
the earthenware drain requires also to be carefully made. This pipe is
curved, and at its upper end has a socket, into which the soil-pipe
enters. A length of brass or copper tubing known as a “thimble” (about
a foot long) should be soldered to the bottom of the soil-pipe; the
rim of this thimble rests in the socket of the drain-pipe and the
space between the two is filled with Portland cement (Fig. 30A). With
the ordinary connection between lead soil-pipe and drain, the former
is apt to become dented by blows, and the latter is very liable to be
partially blocked by the dropping of cement inside the pipe when making
the joint.

=The House Drain= under ordinary circumstances receives waste water
from sinks and baths, rain-water, and the discharge from the closets.

[Illustration: FIG. 31.


We may consider drains under the following heads: material, form,
joints, gradient, ventilation, trapping. The first essential is that
they should be water-tight, so that their contents do not percolate
into the surrounding soil. _Socketed glazed stoneware pipes_ and
_iron pipes_ best fulfil this condition. The best material for making
stoneware pipes is Devon or Dorset, or similar fine clay, which makes
a very strong pipe. Tested pipes free from cracks and flaws must alone
be used. The pipes should be laid in straight lines, each pipe being
arranged with the spigot and not the socket end directed towards the
flow of sewage. The fall should not be less than 1 foot in from 40 to
60. If the fall is less than this amount, artificial flushing from
the upper end of the drain is necessary. Usually branch drains are
made 4 inches in diameter, the main house-drain having a diameter of
6 inches. A larger size than this is seldom necessary. Thus if A, B,
and C be three drains with an equal fall and conveying an equal amount
of sewage, the rate of travel and therefore the flushing force will be
greater, because the depth of the fluid is greater, in A than in B,
and in B than in C. Small drains are more completely self-cleansing
than large drains. The water-tightness depends on the character of the
joints. In this respect _iron drains_ present the great advantage over
earthenware that there are fewer joints and that these can be rendered
permanently water-tight without difficulty by being run with blue lead
and well caulked. To render an earthenware drain water-tight, (_a_) it
must be laid on a solid bed of cement concrete at least 6 inches thick,
so as to prevent sinking, and under the house it should be covered with
an equal thickness of cement concrete (I, Fig. 29). (_b_) The joints
must be made with extreme care, the best Portland cement being used for
the purpose. Clay is inadmissible, as the fibrils of tree-roots easily
find their way through it. The inside of the joint must be raked by the
workmen, before the next pipe is laid, to make sure that no fragments
of hard cement are left projecting in its interior. Such projections
are not uncommon causes of subsequent blockage. Various patent joints
have been used, but they are no better than the above when properly
laid. Just before the drain leaves the curtilage of the house and near
its junction with the sewer, it is trapped, and on the house-side of
the trap (E, Fig. 29) an inlet ventilator is provided. The general
arrangement should be studied in Fig. 29.

=Ventilation of the house drain= from end to end is important, a free
escape of foul gases out-of-doors being induced. The _exit_ is provided
by carrying the soil-pipe up full bore above the eaves, and remote from
windows. One opening alone would not induce a current of air, and the
other end of the drain being trapped from the sewer (B, Fig. 29) it is
necessary to provide an _inlet for fresh air_ at E. This may be placed
a few feet above the ground or at the ground-level. Usually a mica-flap
valve is provided at its upper end, which closes whenever a puff of
foul air attempts to escape from the drain. The necessity for this is
doubtful. Ordinarily air enters at the inlet and circulates through the
drain, escaping at the upper end of the soil-pipe ventilator.

It has been advocated that the soil-pipe ventilator should form a means
of ventilating the sewer as well as the house-drain, the intercepting
trap in the latter (B, Fig. 29) being removed. This is inexpedient, an
element of risk being introduced, in view of the possibility of the
drain or some of the connections of internal sanitary fittings being

[Illustration: FIG. 32.


The drain as ordinarily arranged is trapped from the sewer by an
=intercepting trap=. This is not merely a trap, but a trap provided
with ventilation at its end nearest the house. A form commonly employed
is shown in Fig. 32. B is the junction with the house-drain, at D
is the water-seal, while at C fresh air enters the house-drain. E is
a cleaning eye, through which any chokage can be cleared towards A,
leading to the public sewer. It is important that the intercepting
trap should be accessible in the event of accidental stopping. This is
provided by an =inspection chamber= or =man-hole=. This if close to
the house is provided with an air-tight cover, the inlet ventilator
being conveyed above ground to a convenient point. The man-hole itself
is built with brick set in cement and lined with cement. Note that in
the man-hole itself half-channel pipes convey the sewage instead of
complete pipes.

Sometimes more than one drain-pipe converges to the same man-hole,
and then a more elaborate arrangement than that shown in Fig. 29 is
required, the branch-pipes converging into half-channel pipes in the

=Varieties of Traps.=—Traps are placed at various points of the
house-drainage system to prevent the admission of currents of foul
air into the house. They are all constructed so as to intercept a
water-seal between the drain and the house or yard at the upper end
of the trap. Traps are placed in four positions in connection with
the drainage of a house: (1) near the junction of the house-drain
with the sewer; (2) under the pan of each w.c.; (3) in the open air
at the ground level to receive waste water from bath, sink, and
lavatory basin; and (4) in the waste-pipe close under the bath, sink,
or lavatory, when the waste-pipe is long and apt to become foul; (5)
inside sinks at the upper end of their waste-pipes.

_Intercepting traps_ between the drain and sewer have already been
described. They must always be ventilated (C, Fig. 32 and Fig. 29). A
syphon shape with a water-seal of 3 inches is required, and the trap
should be self-cleansing, that is, whenever the w.c. is used, the fæces
ought to be carried beyond the intercepting trap into the sewer. Other
forms of intercepting trap were formerly used, one of the worst of
which is shown in Fig. 33. With such a trap as this, an accumulation of
filth is inevitable.

[Illustration: FIG. 33.


=A=—Drain entering trap. =B=—Drain leaving trap. =C=—Dipstone.]

=Water-Closet and Slop-Closet Traps= are of the syphon or anti-D type.
The water-seal in these must be at least 3 inches deep, and the trap
must be ventilated by an upright extension of the soil-pipe, otherwise
the water in the trap may be syphoned out when the w.c. is used.
Hellyer’s “anti-D” trap is a lead syphon trap, the calibre of which is
diminished at its bent portion, while the portion of the trap nearest
the soil-pipe or drain is square instead of circular. The constriction
increases the force of the flush of water and thus cleanses the whole
trap, while the square shape impedes the free flow of water, and thus
diminishes the risk of syphonage. Various forms of trap are shown in
Fig. 19 to 34. The most objectionable of these is the old-fashioned
D trap (Fig. 22), the corners and angles of which become fouled, and
consequently the lead becomes corroded.

[Illustration: FIG. 34.



=Gully-traps= are placed in the yard, for the discharge over them of
waste-pipes (Fig. 20). A complete disconnection from the drains is thus
effected. Formerly _bell-traps_ were used for this purpose. In the
Bell-trap not much water can get through, the space A becomes blocked
with dirt, the cover B is often taken off and lost, and then the drain
is untrapped; and even without this, the water-seal is very slight, and
the water quickly evaporates.

=Traps under sinks, etc.=, have been already described (page 166).

Traps were formerly placed at the upper end of the waste-pipe of the
sinks when this was directly connected with the drain. Of these the
Bell-trap and Antill’s trap were most common. The Bell-trap has been
described above. In the Antill-trap the trap is not removable, and the
water-seal is deeper than with a bell-trap. This trap is sometimes used
instead of a gully-trap, but is not so good.

=Efficiency of Traps.=—Eassie has said “honestly speaking, traps are
dangerous articles to deal with; they should be treated merely as
auxiliaries to a good drainage system.”

(1) The trap may have been imperfectly laid to begin with.

(2) It may be emptied by evaporation.

(3) Unless the precautions already mentioned (pages 172 to 173) are
adopted, the flushing of one trap may empty another.

(4) The water of the trap may become impregnated with foul gases, and
these then escape on the house-side of the trap. When a sewer becomes
suddenly charged with a large amount of water, as during heavy rain,
sewer-gases may force their way through the intercepting trap. With a
ventilated drain and soil-pipe these dangers are so small that they may
be ignored.

=Unsyphoning= of traps has been already mentioned. It occurs
particularly when there are several water-closets one over another,
connected with the same soil-pipe. The method of preventing it is shown
in Fig. 28.

=The Examination of Drains and Sanitary Appliances.=—This examination
will involve the detection of (_a_) any deviations from the details
of construction and ventilation of drain and soil-pipe, form of w.c.,
disconnection of waste-pipes, already insisted on; and (_b_) any defect
or leakage in any part of these.

1. _Testing of Water-closet._—The interior of the basin or pan may be
painted with a mixture of lamp-black, size and water. If the usual
flush applied immediately afterwards clears this off, the form of pan
and the flushing power are satisfactory. By removing the wood-work
around the w.c., leakage or spillings of slop-water around the w.c. can
be detected.

2. _Testing of the soil-pipe_ may be effected by one of the volatile
tests named under the next heading. To give the test a fair trial, the
upper end of the ventilating pipe should be temporarily sealed over.

3. _Testing of the drain_ cannot be efficiently carried out unless
access can be obtained to the drain near the sewer. In a properly
constructed house-drain a man-hole is provided for this purpose. Two
chief methods of testing drains and soil-pipes are in use, by smoke or
volatile agents and by water.

The _smoke-test_ consists in filling the drains with smoke, the
assumption being that this will find its way through any faulty joint
or trap, thus indicating the site of the defect. Various arrangements
are employed for pumping the smoke into the drain from the combustion
chamber of a pumping apparatus; or smoke is produced by means of
specially prepared rockets. All outlets or ventilating pipes must be
carefully stopped during the operation, and the place where the smoke
is smelt will then indicate any leaky point.

[Illustration: FIG. 35.


Drain grenades are largely employed for the volatile testing of drains,
the essential constituent being phosphide of calcium. The grenade,
which is attached to a piece of string, is passed beyond the trap of
the w.c., and as the string unwinds the grenade opens and discharges
its contents into the soil-pipe. Or a tablespoonful of strong oil
of peppermint, mixed with hot water, is poured down the highest
water-closet in the house. If this is smelt by another person in the
lower closets, it indicates defective traps or soil-pipe.

All volatile and smoke tests have but a limited utility. They are
useful in detecting defective joints in traps and in the soil-pipe.
They may detect defects in an underground drain; but if no smell or
smoke is perceptible when a drain is tested by this means, the drain
may still be seriously defective. The only absolutely trustworthy
test for drains is the =hydraulic or water test=. The lower end of
the drain is stopped up by a suitable water-tight stopper. Then the
drain is filled with water by means of a tap in the yard, the amount
of water used being approximately estimated by the rate of flow from
this tap. The drain is filled up to the level of the gully-traps in
the yard. If it remains at this level for half an hour, the drain is
sound. More often it leaks so rapidly that it will not fill, or the
level of the water falls quickly after filling, and it is necessary to
strip and repair, or more generally to relay the drain so as to make it

Rats are an important indication of defective drains. The presence of
rats in a house should always lead to a thorough investigation of its



The terms =Sewer and Drain= are used somewhat confusedly. The term
_drain_ should be used to designate the pipes bringing the sewage from
the house into the street-sewer, or any pipes by which the subsoil is
drained; the term _sewer_ being confined to the trunk canals into which
the house drains empty their contents.

Where the water-carriage system of sewerage is adopted, involving the
use of water-closets as described in the last chapter, the sewage may
be carried from the house either into cesspools or into the main sewer.

=Cesspools= are only permissible in isolated country-houses supplied
with water-closets. They should always be situated a considerable
distance from the house, and should be emptied at regular intervals,
the sewage being placed in shallow trenches on the land.

The construction of the cesspool requires careful attention. Its walls
should be of brickwork set in cement, lined inside with cement, and
surrounded by clay puddle. The bottom should have a fall towards one
side, where a pump can be fixed, to remove the more liquid contents.
The depth of the cesspool should never exceed 7 feet. The drain
emptying into the cesspool should be trapped and ventilated, near
its junction with the cesspool; and the cesspool itself should be

In connection with many old houses in towns, cesspools still exist,
sometimes under the basement or near the house, and so built as
to allow soakage in every direction. The surrounding soil becomes
contaminated for a considerable distance, the water in any neighbouring
well is tainted, or leaky water-pipes receive the soakage. The
cleansing of cesspools is always a disgusting process, and even
dangerous to the workmen employed. They incur the risk of suffocation,
and are very subject to ophthalmia. To avoid these dangers a pump and
hose connected with a partially exhausted barrel is employed, but even
with this provision some nuisance arises. In the Bexley cart, which is
used for this purpose, a hose is used to connect the cesspool with an
air-tight cylinder in the cart, into which the contents of the cesspool
are pumped.

A modification of the cesspool system, called the =Pneumatic System=
has been proposed by Captain Liernur. In it the cesspool is not placed
under the house or the courtyard of the house, but under the street
at the angle of junction of several streets. It is made of cast-iron
and air-tight, and is connected with all the houses of several streets
by iron pipes. By means of a powerful air-pump worked by steam, the
cesspool is emptied into barrels in which it is sent directly to farms;
and the barrels being placed on ploughs of peculiar construction, the
manure is discharged from the bung-hole of each barrel and covered over
with earth in the progress of the plough. The pipes tend in this and
similar systems to get clogged with fæcal matter, and large quantities
of water are required to keep them clean, so that the system merges
into that of the use of water-closets, but without the thoroughness of
the latter.

Cesspools have been almost improved out of existence in some
continental towns, by the introduction of movable cesspools,—_fosses
mobiles_,—to which would correspond strictly the tubs and pails used
in some of our large towns. Such movable receptacles have been still
further “improved” by the adoption of _separators_, by which the liquid
parts are allowed to escape into the sewer, while the solid parts
remain comparatively inoffensive. But when this is done, the cesspool
may be as well abolished, as the foulness of the sewage is not greatly
increased by allowing solid as well as liquid excreta to enter it.

=Sewers= are built of glazed stoneware or of impervious brick laid
on a bed of concrete to prevent sinking of any part, the parts being
most solidly put together with cement. Iron and steel pipes are also
used especially when extra strength is required, as when there is some
danger of the pipes sinking. For most small streets circular stoneware
sewers suffice. Oval brick sewers are more suitable for main streets
in which the amount of flow varies greatly. The cross-section of these
should be an egg-shaped oval with the small end downwards, as this
ensures the most rapid current. Sewers should be laid in as straight a
line as possible, and with a fall which will ensure a flow of at least
2½ feet per second. The following rule gives approximately the fall
required for smaller sewers and drains:

 A 4-inch pipe requires a fall of 1 in 40.

 A 6-inch pipe requires a fall of 1 in 60.

 A 9-inch pipe requires a fall of 1 in 80.

For further particulars as to the velocity of flow see page 187.

Where a town is very flat, and a proper fall of sewer impossible,
Shone’s ejectors are sometimes used to raise the sewage. The sewers
are laid in sections, each section falling to a certain point, from
which the sewage is raised by the ejector to a higher level and so
carried to the next section of sewers. Each section has a separate
system of ventilation. The provision of manholes for inspection of
an intercepting trap and of ventilation of the house drain near its
junction with the sewer has already been considered (page 179).

As sewers have commonly to carry away the rain-water in addition to the
waste matter from houses, their size must be regulated accordingly.
The rainfall being very various, the sewers may occasionally become
overcharged and flood the basements of houses. During heavy rainfall
large quantities of road grit are washed into the sewers, the
intercepting gully tanks at the road sides being insufficient to
prevent this.

In addition to the above disadvantages associated with discharging
storm water into sewers, the sewage owing to its increased bulk is more
difficult of disposal, whatever method of disposal be adopted. The size
of the sewers and of storm-outfalls into the nearest river or the sea
must be regulated so that they are equal to these sudden strains on
them; or the =Separate system=, by which the rain is carried in special
conducts to the nearest river, must, in the alternative be adopted. The
objections to this plan are that it necessitates a double system of
sewerage, and does not allow of the useful scouring effect of rain on
sewers. Where it is feasible, and particularly in small country towns,
its adoption is advisable. In such cases the old brick drains are used
for carrying off rain-water, while new _pipe-sewers_ are employed for
carrying the sewage. Such pipe sewers are not liable to become fouled,
and on account of the decreased dilution of the sewage can be made
smaller than brick-sewers.

Sewers being closed conduits containing sewage, it is highly desirable
that the gases resulting from decomposition should be freely diluted.
Such gases in unventilated sewers may find their way through
intercepting traps into the house drain. The danger from this source
has been considerably exaggerated. =Ventilation of the sewer= is,
however, desirable. This has been commonly accomplished by gratings
opening at intervals directly into the middle of streets. In narrow
streets, the stench from street-grids is occasionally a source of
complaint, and may cause malaise and ill-health. Charcoal traps placed
below sewer grids to intercept offensive gases have been found to
be of little use. The best plan is to do away entirely with surface
ventilators, and carry up iron shafts or brick shafts lined with
stoneware pipes above the level of all neighbouring houses. The only
difficulty in adopting this plan is the difficulty in securing premises
to erect such shafts up houses, although no danger attaches to the

Ventilating shafts should be erected at intervals and particularly at
the highest points of the sewage system of a town, the upper end of
these shafts being remote from the windows of any dwelling-house. When
sewers are laid with too steep a gradient, they act as chimneys, the
gases mounting to the higher part of the town, and frustrating attempts
at ventilation on lower levels. Various attempts have been made to
ventilate sewers by artificial means, as by the aspirating effect of
street lamps, etc., but these efforts have not been successful, as the
effect of the up-current only influences a short length of sewer. The
usual method of combined up-shafts and street grids answers fairly
well, but when any complaint of smell from street-grids occurs they
should be replaced by up-shafts. In Bristol and a few other towns
no provision is made for sewer-ventilation, and no ill effects have
apparently resulted. There can be no question that the importance of
sewer-ventilation has been exaggerated. If the sewer has a sufficient
gradient, and is properly laid, and efficiently flushed, so that no
offensive deposits occur, the provision of up-shafts at favourable
points is all that is necessary. Sewer effluvia have been credited with
causing enteric fever, diphtheria, and other diseases. These diseases
rarely if ever owe their origin to this cause. The microbes discovered
in sewer-air have always been those of the outside atmosphere, and not
derived from the sewage. Sewer effluvia might, however, predispose to
such diseases, if exposure to them were frequent or protracted, by
lowering the powers of resistance of the constitution.

=Flushing of Sewers= is required at intervals, in order to remove any
deposits of grit or other solid matter. Flushing is effected by filling
special flushing shafts placed at intervals in the sewers with clean
water and then suddenly releasing this.

_Whenever there is stagnation, a foul odour_ is certain to be emitted.
The cardinal rule with regard to sewage is to keep it in rapid onward
motion, until it has passed the outlet of the sewer. _The introduction
into a sewer of hot water_ or waste steam is an occasional cause of

=The Outfall= of a sewer requires to be large and perfectly free in
order that the progress of the sewage may not be impeded. When the
sewage is discharged into the sea above the low water level, it becomes
backed up in the main sewers when the tide is high. The same condition
of things has occurred when the outfall is into a river below the water
line, or into a tank out of which the sewage has to be pumped. In all
these cases the ventilation of the sewers requires to be perfect, and
great precautions taken to prevent obstruction of the outflow.

In low-lying sewers where the outfall is impeded, mechanical aids are
required to prevent blocking of the sewers. This may be obtained by
pumping at the outfall, to enable sewage to escape at all conditions
of the tide, or to raise the sewage on to land for irrigation. In
the =Shone system= the sewage is raised to the required height by
means of compressed air. In this system the sewage is received into
“ejectors.” These are cylindrical reservoirs, in which is a float on
a counterpoised lever. When a certain quantity of sewage has entered,
a valve opens admitting the compressed air, which forcibly raises the
sewage into a higher length of sewer or to the outfall.



In order to prevent deposit of solid matter, sewers should be
constructed with a sufficient gradient, and of a shape which presents
the least surface for friction in proportion to the amount of liquid to
be conveyed.

All brick sewers should be egg-shaped, with the narrow end downwards.
The egg is formed by two circles touching one another, the diameter of
the upper circle being twice that of the lower.

This shape possesses the great advantage that when the depth of the
stream is diminished the amount of wetted surface of sewer (_wetted
perimeter_) is diminished in equal proportion, whereas in every
other form of sewer it is relatively increased. Thus the friction,
which depends on the extent of the wetted perimeter, is kept down
to a minimum. Where, as in outfall sewers, the volume of sewage is
large, and does not vary greatly in amount, the circular form may be
preferable, as it is cheaper and stronger than the egg-shaped sewer.
Below 18 inches internal diameter, sewers should be circular in
section, and made of stoneware, not brick.

The _velocity of flow_ depends upon (1) the hydraulic mean depth of the
stream, and (2) its inclination or fall.

The _hydraulic mean depth_ means the depth of a rectangular channel
whose sectional area (and therefore the volume of whose current) equals
that of the curved sewer or pipe, concerning which the calculation is
made, and whose width equals the entire wetted perimeter of the sewer
or pipe. It is thus equal to sectional area/wetted perimeter.

In the case of circular pipes, if we take the diameter to be 1, and
assume the pipe to be running full, the sectional area = πr^2, where π
= 3·1416 and r = half diameter.

The wetted perimeter = 2πr, that is, the circumference of the circle
formed by the pipe.

Therefore hydraulic mean depth = h = πr^2∕2πr = 1∕4

Similarly when the pipe runs half full—

h = (πr^2∕2)/(2πr) = 1∕4

The solution of problems where a smaller arc of a circle is occupied by
fluid requires trigonometrical methods, and is not usually needed in

The _quantity of fluid discharged_ in a given time is represented by
the product of the sectional area of the stream into its velocity. The
greater the hydraulic mean depth the greater is the velocity, if the
inclination remains the same.

The _velocity of flow_ is determined by =Eytelwein’s formula=, which
states that the mean velocity per second of a stream of water similar
in form to those now under consideration is nine-tenths of a mean
proportional between the hydraulic mean depth and the fall in two
English miles, if the channel were prolonged so far.

  Thus if f = the fall (in feet) in two miles,
          h = hydraulic mean depth in feet,
           V  = mean velocity per second,
     Then  V  = ·9√(_hf_),
    or if v = velocity per minute, then
          v = 55√(_hf_).

It is more convenient to let f = fall in one mile.

Then the formula becomes v = 55√(h × 2f).

_How much sewage will a circular drain 3 feet in diameter running half
full convey, the fall being 1 in 400?_

Here h = (πr^2∕2)/(2πr/2) = r/2 = 3∕4.

  1 in 400 = x in 5,280 feet (_i.e._ a mile).
       f = 13·2 in a mile.
       v = 55 × 4·4 = 242 feet per minute.
           = 55√(h × 2f).
         S = πr^2∕2 = 3·1416 × 9/(4 × 2) = 3·5343.
   v × S = 242 × 3·5343 = +855·8 cubic feet+, discharged per minute.

_In what way does the size and shape of a sewer affect the velocity
of the sewage flowing through it? If a 12-inch pipe sewer, laid at a
gradient of 1 in 175, gives a velocity of 3½ feet per second, what
would be the velocity if the sewer had a gradient of 1 in 700 (the pipe
running half full in each case); and would this latter velocity suffice
to keep the sewer clear of deposit?_

An elliptical sewer gives greater velocity to flow of small quantities
of sewage than a circular one because it exposes a smaller surface for

  By formula = v = 55√(h × 2f).
         h = 1∕4 ∴ √h = 1∕2.
         f = 1 in 175 = 30 feet in one mile.
         v = (55∕2)√60 = 212·85 ft. per min., _i.e._ slightly over
                                                    3½ ft. per sec.

  In the second case f = 1 in 700 = 7·56 feet in one mile.
                     v = (55∕2)√15·12 = 106·97 feet per minute.

Thus in the first case there is a velocity of 3·55 feet per second,
and in the second case of 1·78 feet per second. The latter velocity
is quite insufficient to keep the sewer free from deposit, 3 feet per
second being the minimum velocity required for that purpose.

_Given a sewer 3 feet in diameter, with a fall of 1 in 1,760, what
would be the relative discharge if the fall were 1 in 5,280?_

  In the first case, 1 in 1,760 = 3 in mile.
                     1 in 5,280 = 1 in mile.
                            h = r/2 = 3∕4.
                            v = 55√(h × 2f)
                                = 55√(3∕4 × 6) = 165/√ = 118.

In second case v = 55√(3∕4 × 2) = 55√(3∕2) = 67·9.

Thus the velocity of the two streams would be as +118: 67·9.+

_Supposing a sewer to have a gradient of 1 in 300, how much would the
velocity and discharge be increased by altering the gradient to 1 in

  1 in 300 = 17·6 in mile.
  1 in 100 = 52·8 in mile.

As h is not given, we must assume it = 1∕4, as it does in circular
sewers running full or half full.

  v = 55 √(h x 2f)
           = 55 √(35·2∕4) = 163 feet per minute.
   v^{1} = 55 √(104∕4) = 281    „       „

The increase in discharge may be similarly calculated.

_Describe the relation existing in a sewer between gradient, volume,
velocity, and size._

  By the formula v = 55 √(_h.f._)
  Where v = velocity in feet per minute.
        h = hydraulic mean depth = (area of cross section of stream)
                                           (wetted perimeter).
        f = fall in feet in two miles.

In circular sewers h = diameter/4.

Thus the velocity varies as the square root of h or f.

The volume discharged varies with the value of the factor v × s where s
= sectional area of stream.

If h remains constant, with a varying volume of s, then the volume
discharged may remain constant. Thus h and v in a circular sewer are
the same, whether the sewer runs full or half full. In a V-shaped
channel the velocity remains the same whatever the depth of the stream,
as its bed and area preserve the same proportions. An egg-shaped sewer
approximates the V shape in form.

Similar volumes of sewage have velocities which vary not only with the
amount of fall, but the size of the sewer. The friction, as represented
by the wetted perimeter, would be much less with sewage half filling
a circular sewer, than with the same amount of sewage forming a broad
shallow stream on the invert of a large sewer.



The water-carriage system of sewage is, as the late Dr. Parkes put it,
“the cleanest, the readiest, the quickest, and in many cases the most
inexpensive method.” But when the sewage is conveyed to the outfall of
the sewer, its ultimate disposal is still one of the most difficult
problems of the present day. Various plans have been adopted, of which
the following are the chief:—

  1. Discharge into running water.

  2. Discharge into the sea.

  3. Separation of solid and liquid parts {By settlement.
                                          {By precipitation.

  4. Filtration through various artificial media or through land.

  5. Irrigation.

  6. Bacterial methods.

=Discharge at once into running water= was formerly the favourite plan,
as it was certainly the most convenient. The sewage was turned into the
nearest water-course, regardless of the facts that this might have to
supply the drinking water of people at a lower point, that the mouth
of the river tended to become obstructed by sewage mud, that valuable
stocks of fish were destroyed, and that the river which had practically
become a sewer was a source of annoyance and danger to all on it or
near it. The enforcement of the Rivers Pollution Prevention Act of 1876
has not been followed by as great improvement as is desirable.

The sewage entering rivers undergoes considerable purification by
subsidence, by oxidation, by the influence of water plants, and
still more by the active work of microbes, causing nitrification of
nitrogenous matter. The vitality of the typhoid bacillus and of the
cholera vibrio when discharged by sewage into a large river is probably
not very protracted; but water from such a river would form a very
dangerous source of domestic supply.

=Discharge into the Sea= is resorted to in seaboard towns. The outfall
must be carried well below the lowest low-water mark, and to such a
point that the incoming tide or wind will not bring the sewage back
upon the shore, or on the shore of neighbouring places.

=Discharge into an Estuary= is only justifiable when the flow of the
river is rapid, when the volume of water passing out to sea is very
greatly in excess of the volume of sewage, and when there is no
possibility of contaminating oyster-layings or beds of mussels or other

Objection has been taken to the above method on the ground of waste of
manure; but modern sewage is so dilute that its profitable utilization
on land still remains a dream.

For a single house or small village, the sewage may be stored in =a
tank, with an overflow-pipe=, out of which the liquid parts escape, and
are systematically used to irrigate land, while the solid parts are
removed at intervals.

A similar subsidence system has been employed on a larger scale, the
liquid parts being irrigated over land, while the solid parts are mixed
with street sweepings, and sold as manure.

If the liquid parts in any such system as this are turned into a
stream, they are as dangerous as the entire sewage, and the legal
prohibition to discharging sewage into streams applies equally to them.

The =precipitation of the solid parts= of the sewage is rendered much
more perfect by the use of =chemical agents=, and at the same time the
dissolved matters are to some extent removed.

Milk of lime has been employed, 6 to 12 grains of quicklime being used
for each gallon of sewage. Secondary decomposition is apt to occur in
the effluent, causing an offensive smell. Salts of alumina, iron salts,
and various combinations of these have also been employed, but with
imperfect results.

The London sewage for some years has been treated by adding 2·5 grains
of sulphate of iron and 3·7 grains of lime to every gallon of sewage;
a reduction of 15 to 20 per cent. in the amount of dissolved organic
matter being secured. Polarite or magnetic spongy carbon is used as a
filter in certain places, the solid and some of the dissolved sewage
being first precipitated by magnetic ferrous carbon (ferrozone). The
Amines process consists in applying a mixture of herring brine and lime
to the sewage. The sewage is stated to be sterilized by this means.
Electrolysis has also been applied to the purification of sewage, as
in the Hermite process. In this process sea-water is electrolysed,
oxygen-yielding compounds and chlorine being produced.

With regard to all the chemical processes hitherto introduced, the
following general statement appears to hold good: they are expensive
and not thoroughly efficient.

=Sewage sludge= is deposited in the tanks in chemical processes
and needs separate disposal. At Birmingham the amount of sludge
produced daily from the sewage of a thousand persons is nearly a
ton. This sludge has been run into rough filter beds and left to
dry or carted away for manure, but in its crude state its manurial
value is very slight. At Ealing it is mixed with house-refuse and
burnt in a destructor. The more modern method is to pass it through a
filter-press, thus compressing it into solid cakes which can be sold
for manure.

=Filtration= of the sewage matter has been accomplished in various

_Intermittent downward filtration_ through a considerable depth of soil
was stated by the Rivers Pollution Commission to be attended with good
results. A porous soil is chosen, and the purified water is received
in drains under it. A large part of the organic matter is removed by
bacterial agency. Frankland’s experiments shewed that upward filtration
through the same media did not purify.

_Filtration through artificial media_ has not been successful with
crude sewage. Precipitation by ferrozone followed by filtration through
polarite is said to be satisfactory.

=Broad Irrigation= purifies the sewage efficiently under favourable
conditions, the possible exceptions being during rainstorms and during
frosty weather. The effluent into the river cannot, however, be
regarded as certainly innocuous, though it is better than the effluent
from most other processes. Sewage farms are not a commercial success.
In such a farm liquid sewage is allowed to flow at intervals over the
land, different fields being irrigated in rotation. Immense crops of
grass are obtained, but the grass is coarse and rank.

The soil to be irrigated should have a gentle slope, and the effluent
be conveyed by subsoil drains about 5 or 6 feet deep into the nearest
water-course. The sewage should be delivered in as fresh condition as
possible, and should be freed from its coarser portions by settlement
or precipitation. The amount of land required is about 1 acre for the
sewage of 100 persons. The irrigation must be on the intermittent plan,
in order that the soil may undergo aeration; as it is only in this
way that the best purifying results can be obtained. The sewage farm
should be well drained by deep-laid agricultural drains. The chief
purification of the sewage occurs in the superficial layers of the
soil. Nitrification ceases at a depth of about 18 inches. The great
point, therefore, is to keep the superficial soil in good condition. A
similar nitrification occurs in earth-closets (page 195). No nuisance
need arise in connection with a sewage-farm, and the supposition that
milk and other products from such a farm are less wholesome than the
same products from other farms has proved to be unbased.

=Bacterial Methods of Treating Sewage.=—Chemical precipitation of
sewage is likely to be completely superseded by _biological or
bacterial_ methods of sewage disposal. When sewage is treated by
filtering through land or by broad irrigation the process is bacterial,
bacteria or microbes in the soil converting injurious organic matter
into innocuous mineral products. The typical process is one of
_nitrification_. The novelty of recent methods is in utilising bacteria
for the whole process of purification, and not only for its final
stages. The object is, in fact, not as in chemical processes to arrest,
but by confining the sewage in tanks to aid and hasten decomposition or
putrefaction. Two kinds of microbes serve in this process; those living
in air, known as _aerobic_, and those living in other gases than air,
called _anaerobic_.

Three biological methods of preliminary treatment of sewage are
employed. (1) Mr. Scott Moncrieff passes the sewage slowly upwards
through a filter 14 inches thick, consisting of successive layers of
flint, coke, and gravel. This is called a “_cultivation tank_.” The
solid sewage becomes liquefied in passing through this medium, the
microbes in the filter dissolving the sewage. (2) In the “_septic tank
method_,” introduced by Mr. Cameron at Exeter, a tank is employed which
is covered in to exclude light, and to a large extent air. The tank
is large enough to hold 24 hours’ flow of sewage. The microbes in the
sewage under these conditions multiply rapidly, attack, and liquefy
the sewage. As in the first process little or no sludge is left. The
ultimate products of the decomposition are water, ammonia, and carbonic
acid, and other gases. The effluent from the tank is comparatively
clear and inoffensive. (3) _Aerobic biological filters_ are employed,
as in Mr. Dibdin’s installation at Sutton, where the filtering material
is coke. The sewage slowly passing through the filtering medium becomes
liquefied, the solid matter being peptonised. This action is in part
at least due to anaerobic microbes. The filtering beds are used
intermittently to allow of aeration, and the liquefaction of solid
organic particles entangled in the filter probably chiefly occurs at
this stage. It is desirable to have small subsidence tanks, for the
removal of large suspended matters and of road debris, etc., before
the sewage is spread over the filtering beds. The material used in the
filter varies. Most commonly coke-breeze has been employed, but coal
slack and other material have also been utilised.

After the preliminary treatment above described, the sewage requires to
be passed over finer filtering beds, in which aerobic microbes complete
the purification by changing the dissolved organic matter into inert
inorganic compounds, by the process known as nitrification. The two
processes run into one another, to some extent going on together.

Hitherto the Local Government Board have required filtration of sewage
through land before any sewage effluent is allowed to pass into a
stream. In view of the successful results now obtainable by bacterial
processes this requirement will be occasionally waived. It is unsafe
to assume, however, that the clear effluent obtained is free from all
disease-producing microbes; and drinking water should not be obtained
from even a very large river below the point of discharge of such an
effluent, without the most efficient sand filtration.



The refuse to be removed from a house consists of fouled water, which
is at least equal in quantity to the water-supply of the house; the
excreta of the inhabitants; and “dust,” which contains, besides ashes,
considerable kitchen refuse; consisting of both vegetable and animal

In dry methods of removing refuse, the “dust” is often added to the
excreta, and the two removed together; or the “dust” may be separately
removed. In either case the foul water, and to a large extent the
urine, remain to be dealt with, and require special drains for their
removal. Thus in large towns, whether dry or wet methods of removing
sewage are adopted, drains for the removal of foul-water and rain-water
will be required, and it is found that they are practically as foul as
if they contained the solid excreta.

The dry methods of removing sewage involve a certain amount of
retention about the house; hence the general name of =conservancy
methods=. Of these the most important are—

 1. The pail system.

 2. The dry-earth system.

 3. The midden or privy system.

=The Pail System= implies in reality the use of a movable cesspool.
The pail may be used alone, or may contain ashes and house refuse, or
some deodorant. Where the pail is used without any admixture of foreign
matter, it should be emptied daily, and care should be taken that the
pails for different houses are not exchanged.

In the =Goux System= the tubs are lined with a composition containing
clay and furnished at the lowest part with some absorbent material such
as chaff, straw, or hay, which serves to absorb the urine and retard
putrefaction. This is, when well managed, somewhat less offensive than
the ordinary pail system.

The pails may be supplied with a deodorant, such as sulphate of iron,
as at Birmingham, Leeds, etc.; they may be packed with absorbent
material, as in the Goux system (Halifax); the ashes and house-refuse
may be deposited in the same pail (Edinburgh, Nottingham); or coal
ashes may be scattered over the excreta (Manchester, Salford); but all
these systems are rapidly being superseded.

Although the pail or tub system is an improvement on the midden
system, it is necessarily a cause of considerable nuisance, and
its replacement by water-closets should be recommended in towns. In
detached country houses it may be retained without nuisance, if the
pail or tub is emptied daily, and its contents at once placed in the
garden beneath a shallow layer of earth. The pails in large towns are
usually collected in specially-constructed closed wagons. In some towns
the pail contents have been burnt in a “Destructor” (page 200) after
having been mixed with ashes. In other towns attempts have been made
to utilise the excreta, either by selling in their crude condition or
after drying and deodorising them by heat. None of these methods repays
the cost of collection. Mixing ashes with the excreta diminishes any
possible value they may possess as a manure.

=The Dry-earth System= is an important modification of the pail system.
In it dry earth or some other material is added to the excreta, thus
converting them immediately into an inodorous mass. Probably the best
contrivances for thus deodorising the excreta, as soon as they fall
into the receptacle, are =Moule’s or Moser’s Earth-Closets=.

It is found that 1½ lbs. of dry earth completely deodorise the
closet each time it is used. Loamy earth is the most valuable material;
a mixture of peat and earth or ashes is very good; sand, gravel, and
chalk are practically useless. It is necessary that the earth should be
very dry, and that it should be finely sifted. If the earth is damp,
decomposition of the excreta speedily occurs. The act of sitting and
rising works a hopper which scatters a supply of earth.

Charcoal and sawdust have also been used in connection with Moule’s
or Moser’s closet, and with good results. Charcoal has been obtained
cheaply for the purpose from street sweepings, and from seaweed,
as in Stanford’s closet, in which 1∕2 lb. of charcoal from seaweed
is used each time. Mr. Stanford found that while dry clay absorbs
only 4 to 5 per cent. of water, dry charcoal prepared from seaweed
absorbs 14·7 per cent. The best material, however, is dry earth, but
it must be thoroughly dry. The microbes in the earth disintegrate the
excreta, converting them into mineral compounds, such as nitrates.
Even the paper used disappears. Hence the same earth may be used over
again after being stored dry for six weeks. Whether the excreta of
an infectious patient are freed from infection by this process is
doubtful; if not, the infection might be scattered by means of dust.

The dry earth system is more expensive in use than the pail system, and
although applicable to villages and isolated houses, is quite unsuited
to large towns, owing to the practical difficulties connected with
the procuring and storing of dry earth. The dry earth closet requires
frequent attention, in addition to not being so convenient as the pail
closet; and there is much less manurial value in the contents of earth
closets than in those of pail closets.

The advantages of the earth-closet as compared with the water-closet
have been thus summarised by the late Sir Geo. Buchanan. “It is
cheaper in the original cost, it is not injured by frost, it is not
damaged by improper substances driven down it, and it very greatly
diminishes the quantity of water required by each household.” These
advantages only accrue when the system is perfectly worked, and do
not counterbalance the immense advantage and greater safety of the
water-carriage system in towns.

=The Privy or Midden System=, involving the use of a fixed receptacle,
is still prevalent in many towns as well as in innumerable villages.
In its worst form, the receptacle consists of a pit with sides of
porous materials, allowing percolation of filth in every direction;
and in this pit the excreta of whole households are allowed to collect
for months. It has been improved by providing a cover to keep out
the rain, and thus retard decomposition; still more by providing a
drain for the excess of liquid; and by making the sides and bottom
of the pit impervious to moisture. The addition of dry ashes to the
excreta tends still further to prevent any smell; and the greatest
improvement of all consists in raising the receptacle above the ground
level, and providing for easy cleaning from the back. The raising of
the receptacle involves a diminution in its size, and so prevents the
retention of putrefying matters near a house for a long time.

The model Bye-laws of the Local Government Board recommend a capacity
for the privy not exceeding 8 cubic-feet, the provision of means for
the frequent application of ashes, dust, or dry refuse; they forbid
any connection between the privy and the drain; insist on its being
at least 6 feet from a dwelling-house (too low a limit); and require
a flagged or asphalted floor at least 3 inches above the level of the
surrounding ground.

The _Nottingham tub-closet_ forms a link between the pail and midden
system. It is really a small movable middenstead, used for receiving
excreta, vegetables and ashes.

Even when carefully supervised, middens are almost certain to be
productive of evil. They possess two great disadvantages as compared
with pails or dry closets. (1) The time between collections of excreta
by the scavengers is much longer; and (2) the receptacle for the refuse
is part of the structure of the building, and cannot easily be renewed
when it has become saturated with excreta.

The use of pails or dry-earth closets is a great improvement on the old
middens, but even these compare very unfavourably with water-closets
in two respects. (1) The excreta require to be retained about the
house for a longer or shorter period, whereas with an efficient
water-carriage system, they are at once projected into the sewer. (2)
In removing the excreta, the weight of the receptacle has to be added
to that of the excreta, while in the water-carriage system, the water
serves as the means of transport.

In villages and isolated houses, where no drains are provided for waste
water, and the dry system of closets is adopted, the =disposal of waste
water= requires special provision. Very commonly the slops are thrown
out of the door, and soak into the ground about the house. They should
be carried by means of a waste-pipe into a water-tight cesspool, remote
from the house, whence they can be pumped into a field, or carried
away by special conduits.

=Relative Merits of Dry and Wet Methods.= No absolute answer can be
given in exclusive favour of either plan. Each is the best under
different circumstances; the dry method being chiefly suitable for
small villages, and for temporary collections of people, as in camps;
and the wet method for towns. The question of value of manure does not
enter into the problem, as it seldom repays for carriage.

The =objections to the water-carriage system= are really due to its
not being carried out in an efficient manner. When sewers are properly
laid; when they, as well as house-drains, are freely ventilated; when
house-drains are efficiently trapped and ventilated near their junction
with the sewer; when the drains are efficiently flushed, and the
outflow from the sewer is unimpeded, the objections disappear.

These objections are that—(1) the sewers, as underground channels,
transfer effluvia and the germs of disease from one place to another;
(2) pipes become disjointed owing to being badly laid, and the ground
is contaminated; (3) the water supply is in danger of receiving
impurities from the sewers. These objections do not hold good in
practice. The contamination of water-mains or of wells from sewers
implies gross carelessness in the method of laying of sewers or pipes.

The only objections which are of any force, are (4) that water-closets
require a large amount of water, and the sewage obtained is greatly
diluted, and consequently diminished in value; while (5) the disposal
of such an amount of water, in the case of a large inland town, is a
problem of the utmost difficulty. Modern engineering enterprise by
bringing water from a greater distance, and by aiding the discharge of
sewage when necessary by pumping, has overcome these difficulties.

There are many =objections to the dry methods= of removing excreta. (1)
Whatever dry method be adopted, the excreta are retained for some time
in or about the house, instead of being immediately removed.

(2) Although the initial outlay in closets and sewers is less than with
the water-carriage system, there is the constantly recurring expense of
removing the excreta, as well as of cleansing the pails, etc.

(3) In the dry-earth closets, the provision of dry earth or other
material involves some expense.

(4) Whatever dry method be adopted, sewers are always required to carry
off the foul water, as well as liquid trade products, and a certain
proportion at least of the urine. It is impossible to supply sufficient
dry earth to absorb all the urine and slops of the population.

Thus, as the Indian Army Sanitary Commission said, speaking of
barracks, “to have two systems of cleansing stations—a foul-water
system, and a dry-earth system—would simply be paying double where
one payment would answer; or, if all the excreta, solid and liquid,
are to be carried away, this must be done at a cost ten times greater
than that which would be necessary, if all the excreta were removed by

With some of the dry methods, as where middens or cesspits are drained
into the sewers, the sewer-water is more offensive than in towns
supplied with water-closets. When a midden or cesspool is drained, the
principle of conservation, which distinguishes the dry system from the
wet, is practically abandoned; and not only so, but the solid matters
still remain to be disposed of, by a tedious process.

(5) The dry systems, involving the retention of excreta about the
house, poison the atmosphere. In all towns where the refuse matters are
not removed immediately, there is a high mortality, especially among

On the other hand, the introduction of the water-carriage system into
large towns, with the abolition of midden-heaps and cesspools, has
been followed in nearly every case by a diminution in the death-rate,
and especially a considerable diminution in that from such diseases
as enteric fever. It has furthermore increased the comfort of life,
and removed those serious nuisances which are inevitably associated
with privies and pail closets, and to a less extent, when care is not
exercised, with earth closets.


In an ordinary household the disposal of ashes from fires, of broken
pots and cans, of waste-paper, and of vegetable and animal debris form
a serious difficulty. The difficulty is one that can be minimised by
the careful housekeeper. Old newspapers, etc., may be sold, though
their value is very small; other waste-paper should be burnt. All
vegetable and animal debris should be burnt. This may be effected
without nuisance if coal-fires are in use, by placing potato-peelings,
cabbage leaves and similar substances under the fire until thoroughly
dried, and then burning them. The careful housewife will not waste
bones, but utilise them for soup. After being boiled they are much less
liable to putrefy in the dust-bin; but should even now be burnt in
the fire. If this plan be pursued, the contents of the dust-bin will
be simply ashes, broken pots and cans, and a few cinders—here again
a sifter is desirable—and no nuisance can arise. _It is only organic
refuse that smells._ If only gas or paraffin stoves are in use, as
during the summer months, any possible nuisance in connection with
the dust-bin is minimised by allowing all refuse to dry before it is
placed in the dust-bin, or by wrapping all putrefiable substance inside
several layers of newspaper.

In _emptying the dust-bin or ash pit_, care must be taken that the
bottom is thoroughly scraped out. It is well to keep some quicklime
(thoroughly dry) for sprinkling on the bottom and sides of the
receptacle each time after it is emptied. This greatly helps in keeping
it dry and diminishing nuisance during summer.

In many households a separate receptacle is kept for what is known
as “hog-wash,” containing waste-food, often in a foul and putrefying
condition. In well-ordered households, except in hotels and similar
establishments, there is no necessity for a “hog-wash” tub, and its
presence argues wastefulness and carelessness. Food which cannot be
eaten because it has “gone bad” should be burnt.

Two forms of receptacle are used for house-refuse, an ash-pit or a
dust-bin. An =ash-pit= is a fixed receptacle for the reception of
house-refuse. In many towns the same receptacle is used for excreta.
Then we have a privy or privy midden, according to size (see page 196).
Ash-pits for household refuse alone should be small, so as not to hold
more than a week’s refuse. No part should be below the ground level.
The floor and walls should be lined with impervious smooth cement, and
the ash-pit should have a hinged cover to keep out rain, and a door on
one side to facilitate emptying. The ash-pit should be at least six
feet distant from any wall of the house. Even the best constructed
ash-pit is as much worse than a dust-bin, as a privy is worse than a
pail closet. A fixed is always less easily cleansed than a movable

A =dust-bin= is usually made of galvanized iron with a tight-fitting
lid. This receptacle can be kept clean, and can be carried without any
transference to another tub direct to the cart.

The =removal of house refuse= constitutes an important part of
municipal work. In most towns it is carried out weekly, sometimes less
frequently, while in some towns removal twice or three times a week is
secured. A daily removal is carried out in a few towns, and this is by
far the best plan, as decomposition and the dangers associated with it
have then no chance of becoming serious. The house refuse should always
be conveyed through the streets in covered carts.

The =disposal of house refuse= constitutes a problem of increasing
difficulty. Unfortunately in the suburbs of many towns it is deposited
on low-lying land in disused quarries and brickfields. When land has
been thus levelled, it often next appears as “an eligible building
site.” A very common practice has been to excavate gravel and sand upon
the site of proposed dwellings, and allow the excavation to be filled
with dust-bin refuse. Before building on such a soil it is necessary
to excavate down to the virgin earth, and to render it impervious by a
layer of cement concrete.

A second method is to _sift and sort the refuse_, separating by
means of sieves the finer ash and dust from the coarser parts. This
is usually carried out in a large dust-yard adjoining a river or
railway-siding. The “breeze,” consisting of cinders and coals, along
with the fine ash, are sold to brickmakers; the “hard core,” consisting
of clinkers, broken crockery, etc., is used for road making; and the
“soft core,” consisting of animal and vegetable refuse, to which is
often added stable manure, is sold for manure. Iron, tin, paper, rags,
bottles, and corks are separately collected and sold. This disgusting
process, often carried on by women, is now gradually being disused.

A third method is to _cremate the house refuse_. This has been done
to a large extent by burning the house refuse for making bricks
(page 124). This method of slow and imperfect combustion necessarily
involves a nuisance. A more elaborate means of securing the same
end is by the modern =Destructor=, which has been gradually brought
towards perfection. A destructor is a large furnace, in which, after
the fire has been first lit, the combustible matter in the house
refuse suffices to keep it alight. Various mechanical devices are in
use for emptying the trucks of house refuse on to the fires without
handling it, for clearing out of the fire the inorganic refuse, and for
ensuring sufficiency of draught. The amount of draught has in the older
destructors been dependent upon the height of the chimney. In some
more recent destructors the same end has been more efficiently secured
by injecting a steam blast into the furnaces. A temperature of about
2,000° F. is reached in certain parts of the destructor, the rapid
draught ensuring enormous heat. In view of the possibility of a portion
of the smoke not being completely burnt, a second “fume cremator” is
often provided, through which the products of combustion in the furnace
are passed. The fuel in the “fume cremator” is coke. Besides incomplete
combustion of combustible material, which is rare when the fume
cremator is provided, the escape of fine dust up the chimney requires
to be guarded against. This is partially prevented by ledges near the
bottom of the chimney. In a destructor the house refuse is reduced
to about one-third of its original bulk, the residue being innocuous
clinker, metallic refuse, and dust. This material can be utilised for
making roads, and in the manufacture of mortar. The waste heat of the
destructor has been partially utilised for various purposes. This
method of disposal of house refuse is usually the best available for
large towns, and offers the additional advantage that no nuisance is
caused by the deposit of offensive material in neighbouring districts.



Lord Bacon said: He who builds a fair house upon an ill seat committeth
himself to prison.” The first considerations, therefore, in choosing
a house are those of aspect, surrounding objects, and soil. On the
first of these considerations, that of =aspect=, Thomas Fuller’s quaint
remarks give the essential points. He says:

 “Light (God’s eldest daughter) is a principal beauty in a building;
 yet it shines not alike from all parts of heaven. An east window
 welcomes the beams of the sun before they are of strength to do any
 harm, and is offensive to none but a sluggard. A south window in
 summer is a chimney with a fire in it, and needs the screen of a
 curtain. In a west window in summer towards night the sun grows low
 and even familiar, with more light than delight. A north window is
 best for butteries and cellars, where the beer will not be sour from
 the sun shining on it.”

A workroom or study requiring steady light, should point north or some
point between north-east and north-west. A breakfast room should face
north-east to south; while one aspect of a drawing-room should be
south-east to north-east. Store-rooms, dairies, larders, should have
a northerly aspect. It is preferable, as a rule, for the house not to
face in the direction of the four points of the compass, but diagonally
to these.

=Surrounding Objects= of an objectionable character, as factories,
noisy or offensive trades are to be avoided. The possibility of
neighbouring cesspools contaminating the water supply must be
considered. _Trees_ close to a house are objectionable, rendering it
damp, and preventing the free access of sun and air. More remote from
the house they form a useful shelter, especially when to the north or

The banks of _water courses_ are to be avoided for similar reasons. If
there is a choice, the _slope of a hill_ should be selected; and it
is essential that no part of the dwelling should rest against sloping
ground at a higher level. Rank vegetation indicates a damp clayey soil.

The main point is to secure that the house shall receive ample =light=
and ventilation. In calculating the =amount and intensity of sunshine=
which a house built on a given site will secure the variations
according to season must be remembered. The direction (orientation)
of the sun is the same all the year through; but the altitude of the
sun varies with the latitude. Thus in a house facing directly south in
the latitude of the south of England the sun’s altitude at noon on the
21st of December is 15° 4´, on the 21st of June 62° 4´. A ray of light
entering the highest point of a window facing south at each of these
seasons will illuminate a much larger part of the room in summer than
in winter. Not only so, but inasmuch as it enters the room more nearly
vertically it is more powerful than when entering at an angle more
nearly approximating a horizontal direction, in accordance with the
general law that the intensity of illumination falling on a horizontal
surface (as the floor of a room) is inversely as the square of the
width of the area embraced within the same angle of incidence of light.

In houses in a street the angular aperture through which light enters
is greatest in the upper stories. It may be increased (_a_) by
increasing the height of rooms; (_b_) by carrying the window heads
nearly to the level of the ceiling; and (_c_) by avoiding the proximity
of other buildings which would impede the access of light. Fig. 36
shows the importance of the last consideration. This represents a
three-storied house in a street, of which the opposite house L is of
the same height. It will be observed that each room is divided into
two regions of different degrees of illumination by a plane Lm, formed
by a line connecting the ridge of the roofs of the houses on the
opposite side of the street with the interior surface of the rooms and
touching the uppermost point of the window in transit. Below this line
there is “sky-light” sufficient in quantity; above this line light
is insufficient in amount and is diffused and reflected. The area
receiving sufficient light increases from the ground floor upwards. We
have already seen that its intensity similarly increases in the higher
stories, the rays of light being more nearly vertical in these.

[Illustration: FIG. 36.


 The amount of sky-light visible can be expressed in terms of the
 _angle of aperture_, i.e. the arc of sky visible at any given point
 _a_ in the room. Thus in Fig. 36 the triangle of aperture _bac_ is
 greater than _b´a´c´_, and this greater than _b´´a´´c´´_. The sides of
 the angle of aperture, it will be seen, are formed by drawing one line
 from the point a to c, which, if prolonged, would touch L, and another
 line to _b_, which passes through the highest point of the window.

The amount of light received in a dwelling-house is largely determined
by the =width of the street= and the distance between the backs of the
houses in adjacent streets. The model Bye-laws of the Local Government
Board insist that no new street shall be less than 36 feet wide if it
exceeds 100 yards in length or is intended to be a carriage road, not
less than 24 feet in any case. Furthermore, a new house must have in
the rear an open space exclusively belonging to the house, at least
150 square feet in area, and free from any erection above the ground
level. This must extend along the entire width of the house, and must
never measure less than 10 feet from every part of the back wall of the
house; the distance must be at least 15 feet, if the house is 15 feet
high; 20 feet if 25 feet high, and 25 feet if 35 feet high or more.

[Illustration: FIG. 37.


Streets should never be less in width than the height of the houses in
them; and a line drawn from the ridge of the roof to the foot of the
wall of the opposite houses (Fig. 37) or in the rear to the foot of the
wall or fence dividing the back yards of contiguous houses, should not
make an angle of more than 45º with the ground (Fig. 37). This is the
angle required for new buildings in the residential parts of Liverpool,
and was proposed for London, but unfortunately not made obligatory.
The size of windows is discussed on page 216. The light received in
a given house is often diminished at corners of streets by contiguous

The =Soil= has an important influence on the healthiness of a site.
The relative merits of the different kinds of soil are discussed on
page 219. Undrained soils of whatever kind are bad, and made-soils are
always to be regarded with profound distrust.

The =planning= of a house should be carefully considered. The
principle is that the sun should enter every living room at some time
of the day. The relative positions of fire-place, window, and door
in each room are important. With the sole window of a room in the
same wall as the fire-place the area ventilated is the least, with it
situated on the opposite wall the area ventilated is the greatest.
The door should be as remote from the window as possible, in order
to secure occasional perflation of air; the two being preferably on
opposite walls. Staircase windows are indispensable to secure through
ventilation of a dwelling. Houses constructed “back to back” cannot be
properly ventilated as no through current of air is possible. Hence the
necessity for open yards at the area, as well as air-space in front of
the house. (Fig. 37).

In the =construction= of a house, apart from access of light and air,
the main problems are to secure dryness and equability of temperature.
We shall consider in this connection the materials used in the
construction of walls, floors, and roofs.



In this country walls of houses are usually built of brick, stone,
timber, or concrete, of which the first two are the most important.
Timber is, owing to its inflammability, only allowed to be used in
towns under special restrictions. Bricks and stones are bonded together
and imbedded in mortar or cement.

There are several kinds of =bonds= in brickwork, of which the strongest
is the _English_. This consists of alternate courses of “headers” and
“stretchers,” the former being bricks carried through the wall from
face to back, the short end showing on the face, and the latter bricks
laid lengthwise along the face of the wall. Hence the wall is held
together in every direction. A _Flemish bond_ consists of alternate
headers and stretchers in the same course. It is used where a specially
smooth wall is desired, but is not so strong as the English bond.

=Bricks= are generally of a uniform size, of 9 inches in length by
4½ in width and 2-3∕4 inches in thickness. Those bricks which are
heaviest and hardest are generally the most durable; bricks of good
quality when knocked together give a clear ringing sound.

The relative conductivity for heat of brick as compared with other
materials, is shown in the following table, from Galton, which gives
the units of heat transmitted per square foot per hour by a plate 1
inch thick, the two surfaces differing in temperature 1° Fahr.:—

  _Stone—ordinary free stone_  13·68
  _Glass_                         6·6
  _Brickwork_                    4·83
  _Plaster_                      3·86
  _Fir planks_                   1·37
  _Brick dust_                   1·33

It is evident that in this respect, brick walls compare very favourably
with stone walls, and are much more economical of heat. Increased
conductivity of a material may be counteracted by increased thickness.

Brick is very porous, as shewn by its power to absorb moisture. A good
brick can absorb from 10 to 20 per cent. of its weight of water; while
good granite only takes up 1∕2 per cent., sandstone usually from 8 to
10 per cent., marble only a trace, and Portland limestone 13½ per

Being porous, brick allows the passage of a considerable amount of air,
unless its pores are occupied by moisture. The following table, from
Galton, shews the number of cubic feet of air which every hour pass
through a square yard of wall-surface of equal thicknesses, built of
the following materials, there being a temperature of 72° Fahr. on one
side the wall, and of 40° on the other:—

  _Wall built of brick_                7·9 _cubic feet_.
        „       _quarried limestone_   6·5      “
        „       _sandstone_            4·7      “
        „       _limestone_           10·1      “
        „       _mud_                 14·4      “

=Mortar= should consist of clean sharp sand and slaked lime, usually in
the proportion of three of the former to one of the latter. Grouting,
or liquid mortar, is merely ordinary mortar to which a larger quantity
of water has been added. It is used for filling up the crevices between
the brickwork about every fourth course, and is required to a greater
extent in stone work, owing to the difficulty in filling up spaces left
by inequalities in the stone.

The sand used in mortar should be free from small stones. It should not
contain any earthy or clayey matters, as these greatly diminish the
adhesive quality of the mortar, which depends on the combination of the
sand and lime. All the sand used in a building should be washed, unless
it is perfectly clean, in order to remove impurities. Many builders use
an inferior mortar, in which other materials, such as “road scrapings,”
are substituted for sand. Sand taken from the sea-shore is unfit for
making mortar, as the salt contained in it is apt to deliquesce and
weaken the mortar.

=Lime= is obtained by burning chalk or limestone in a kiln. Thus CaCO₃
= CaO + CO₂. There are three kinds of lime: (1) Fat or quicklime, used
for internal plastering, (2) stone lime, used for ordinary building
work, and (3) hydraulic lime, used for building in damp situations. The
last named contains a quantity of silicates, and sets under water.

Common mortar crumbles away, if laid under water before it has had time
to harden.

=Portland cement= is an artificial cement, of a dark grey colour. It
is made by grinding chalk, mixing it with blue clay or river-mud in
certain proportions, and then burning it in a kiln and afterwards
grinding it to a fine powder. It is used, mixed with sand, for external
plastering (“compoing”) of walls, for making concrete, or instead of
lime for making mortar if extra strength is required.

=Compo= consists of Portland cement and sand, and is used for covering
walls when an impervious smooth surface is required, and for keeping
out rain. It is laid on in two coats. The first or rough coat 3∕4 inch
thick, is composed of one part cement to 5 parts compo sand, _i.e._
coarse sand mixed with fine beach. The outer or fine coat is composed
of two parts fine or washed sand to one part cement. To “render”
or “compo” a wall is to cover it with this material. The internal
plastering of a chimney flue is called “pargetting.”

=Concrete= is of two kinds, lime or cement concrete. It is composed of
three parts broken ballast or large beach, two parts of sand, and one
part of lime or cement. Lime concrete has no resisting strength, and is
only used for surrounding drain-pipes, or where no great strength is

=Stone= varies very greatly in character. It is uncommon for the whole
thickness of the walls of a house to be built of stone; usually there
is merely a facing of stone and a backing of brickwork. If good stone
is not available, the less it is used the better.

The stone chosen should be durable, and able to resist the action
of the sulphuric, sulphurous, and carbonic acids absorbed from the
atmosphere, and brought in contact with it by means of rain. The stone
of which a considerable part of the Houses of Parliament consists is
dolomite, a double carbonate of lime and magnesia. The acid fumes in
the air produce on its surface sulphate of magnesium, which is washed
away in successive layers.

If the stone presents any stratification, it should be laid in the
wall in the same position as that in which it was originally deposited
in the quarry. Thus, any planes of stratification will be horizontal,
and the scaling off by the action of frost and rain is minimised.
Comparatively homogeneous stones, such as granite and millstone-grit,
can be laid in any position. In testing the character of any stone, the
least porous, densest, and most resistent to crushing, will as a rule
be the most durable.

The chief difficulty in the use of stone for the walls of houses, is
that of keeping out the wet. To obviate this, stone-houses are often
built of great thickness, and are consequently cooler in summer and
warmer in winter.

In and near large towns brick is chiefly used for walls of houses,
and stone employed only for window-sills, columns, steps, etc. It is
even more important in these cases to carefully select the stone, as
the parts where it is placed are those most exposed to the weather. If
a soft, friable freestone is used, after a sharp frost large scales
are seen falling off in flakes, owing to the freezing and subsequent
thawing of the moisture in the stone.

_Portland stone_ is the best-wearing stone to be had in the
neighbourhood of London. _Bath stone_ is also considerably used, but it
varies greatly in quality, and should be very carefully selected. For
landing-steps and paving, _Yorkshire stone_ is extensively used, but
artificial cement pavings are replacing it to some extent. Most kinds
of stone can only be economically used near the quarries from which
they are derived.

The _Slate_ used for roofs is an altered form of clay, possessing a
laminated structure. The ease with which it splits along the planes,
renders it peculiarly suitable for this purpose. The Welsh slates are
considered the best.

=Terra-cotta= is made from certain kinds of clay, mixed with glass,
pottery or sand; then ground up, strained, and kneaded; and lastly
thrown into moulds and baked in a kiln.

=Iron and Wood= have occasionally been employed alone in building
houses. The former, owing to its good conducting powers for heat, is
cold in winter and hot in summer; while the latter becomes rotten
from exposure to wet, and is also very combustible. Corrugated
iron buildings lined with wood are also employed, but are not very

For roofs, slates or tiles are the materials most frequently employed;
but occasionally lead and corrugated iron are used, also thatch in
country places, and tarred felt for temporary buildings.

=Lead= is the most suitable metallic covering for roofs, as it
is durable and easily worked. It is, however, heavy and demands
considerable strength in the timbers by which it is supported.
=Galvanized iron= has also been largely used. It is cheaper and lighter
than lead. Both lead and zinc require very careful laying if they are
to be weather-tight.

=Thatch= protects the interior of a house well from extremes of heat
and cold.



In preparing to build a house, or in entering into a house already
built, the following requisites should each receive careful attention:—

1. The site of the house should be healthy, and its relation to
surrounding objects in accordance with the laws of health. (See page

2. The house should be warm in winter, and cool in summer.

3. It should be always dry.

4. There should be an abundant and uninterrupted supply of air.

5. The water supply should be abundant, conveniently arranged, and pure.

6. The excreta and waste-water should be immediately removed from the
house and its annexa.

The three last requisites have already received consideration. Of those
still to be considered, =dryness= is the most important. A damp house
is certain to be an unhealthy one. It is this for two reasons:—1st, it
is a cold house, as damp walls, like damp clothes, conduct the heat of
the body away much more rapidly than dry walls; 2nd, if the pores of
the bricks are occupied by water, air cannot pass through, and thus the
ventilation and purification of the house are greatly impeded. Damp may
arise from the ground on which a house stands, or from the rain beating
against the walls, or from a defective roof. Unless special means are
taken to prevent it, moisture rises by capillary attraction through
brick after brick.

The =Foundation= requires to be solid and substantial, otherwise
sinking occurs, with cracking of the walls, resulting in an unsafe
condition, and an exposure to rain and wind.

In making the foundation for a house, the ground should be excavated,
so as to secure a solid bed of earth or rock not liable to be affected
by the weather. A continuous bed of the best cement concrete should
then be laid, not only under the walls, but covering the entire site
of the house, and extending on every side at least 6 inches beyond the
footings of the wall; and for footings it should never be less than 18
inches thick. The concrete serves two purposes: it, to a large extent,
cuts off the entrance of the ground-air through the basement floor
into the house; and prevents the entrance of damp into the house from
below. To further ensure dryness where the floor is below the level of
the adjacent ground, a _dry area_ is frequently provided, that is, a
closed chamber lined with stone or cement below the ground level of
the house, and surrounding the underground part of its four walls, or
a hollow wall is built below the ground-level, as shown in Fig. 38.
Neither a dry area nor a hollow wall constitutes the best arrangement,
as the cavity is usually inaccessible, and rather aids than hinders the
entry of the ground air into the house. The best plan is to provide a
solid wall, impervious to both moisture and air. A vertical layer of
roofing slates is sometimes used for this purpose; or, still better, a
narrow cavity about 1∕2 to 3∕4-inch wide is provided in the body of the
wall, and this is run full with molten asphalte.

The =Walls= of the house must be provided with a “=_damp-proof
course_=” carried through their whole thickness, slightly above the
highest point at which the ground is touched. It may be formed by (1)
sheet lead, which possesses the disadvantage of being costly; (2) two
layers of ordinary roofing slate, set in cement, with broken joints,”
_i.e._ the joints of the upper layer over the centre of the slates
below them; (3) a layer of good asphalte, about ¾-inch thick; (4)
perforated glazed stoneware slabs; or (5) two or three courses of hard
blue Staffordshire bricks, laid without mortar. The use of asphalte is
an excellent plan, and is now commonly adopted in good buildings.

[Illustration: FIG. 38.


 _a_, _a_—Damp-proof courses. _b_—Level of neighbouring ground.
 _c_—Floor-boards. _d_—Floor joist. _f_—Vertical space in wall.
 _g_—Concrete under foundation and over site of house.]

This suffices when there is no basement. If there is a basement an open
area around the house is desirable. Where for a given wall this cannot
be secured, the vertical damp-proof course already described must be
made to extend from the foundations well above the ground level. The
open area, however, should be insisted on whenever practicable. The
damp-proof course protects the walls from damp proceeding from the soil
around or beneath the house.

It is necessary also that the walls above the level of the ground
should, as far as possible, be kept free from damp. =_Damp walls_=, not
due to ascent of moisture, =_may be caused by_=

(1) Rain falling on window-sills which do not project beyond the walls,
and consequently do not throw the water clear of them. This is remedied
by constructing the window-sills so as to project beyond the walls, and
“throating” them to prevent rain from running along the bottom of the
sill. The throat is shown at _a_, Fig. 39.

(2) Rain falling on cornices and other projecting portions of the wall
itself. The evil from this source may be diminished by sloping the top
of the projection, downwards from the face of the wall.

(3) Parapet walls, gables, etc., not being properly covered with
coping. All such walls should be topped with a projecting slab of
stone, or with a damp-proof course under the top course of bricks,
which should be laid on edge.

(4) Overflow from defective roof-gutters or rain-water pipes. In this
case, either clearing out, repairing, or renewing is required.

(5) Rain beating against the walls. This as a rule produces no great
harm, if the walls are well constructed. Most of the water runs off as
it falls on the surface. It is advisable, however, to protect a much
exposed wall by a coating of Portland cement, or in extreme cases with
slate. Various impervious paints have also been employed.

[Illustration: FIG. 39.


 Showing stone sill “weathered” at _i_, and “throated” at _a_.
 _b_—Wall. _c_—Inside plaster of room. _d_—Window-board. _e_—Oak sill.
 _f_—Beading and _g_—bottom rail of window-sash. _h_—Window. _j_—Iron
 tongue let into slot in _i_ and _e_ to prevent rain driving in.]

If it is not proposed to coat exposed surfaces of brickwork, the
wall may be formed of two parallel walls, two inches apart, and tied
together by a sufficient number of bonding-ties of iron or glazed
stoneware, or some other non-absorbent material. This arrangement is
shown in Fig. 40.

An excellent plan is to fill in the narrow space between two such
walls, as the building proceeds, with asphalte or slab slate, thus
forming a _vertical damp course_, in the same way as below the ground
level. The evils arising from damp can be avoided in every new house
by proper methods of construction. In an old house, however, they are
much more difficult to remove. The dampness is indicated on entering,
by a peculiar mouldy smell, and by the discolouration and destruction
of wall-papers, and dry rotting of floor timbers. In such a case a damp
course may, with care and patience, be inserted in the wall, and the
soil under the basement may be covered with concrete, and a dry-area
excavated around the basement. Free ventilation under the floor-boards
of the lower floors also helps in keeping the house dry.

[Illustration: FIG. 40.


_a_—Cavity. _b_—Tie. _c_—Floor-joist. _d_—Wall-plate. _e_—Concrete
foundation of wall.]

The _thickness_ of the walls of a house requires to be sufficient to
ensure stability, to keep out the damp, and to prevent a too rapid loss
of heat from the walls. The relative merits of the different materials
employed for these purposes have been already considered. A thin-walled
house is hot in summer, and cold in winter. The upper stories of houses
are often built with too thin walls, the result being chilly bedrooms.
A single-brick wall (9 inches thick) will rarely keep out the weather
effectually, and frequently a brick-and-a-half wall (14 inches thick)
is insufficient for this purpose. The bricks should be so interlaced
as to “bond” or tie the wall together in all directions. The strength
of walls may be increased by the introduction of hoop-iron between the
courses of brickwork.

In the construction of fire-places and chimneys, it is important to
avoid the proximity of timber and wood-work to the inside of flues, as
this is a common cause of fires.

Inside Coverings of Walls.

=Plaster= is made of lime mortar, or cement mortar; the former is
generally preferred for domestic dwellings because it remains porous
and moisture does not condense on it.

In houses built by speculative builders, the plaster commonly used
consists of a mixture of lime with road scrapings. The result is a
composition which unless supported by the wall-papering, is soon

Ordinary plaster consists usually of three layers. The first is laid on
with a mixture of about equal parts of lime and sand with long ox-hairs
if required for ceilings. The second coat consists of slaked lime,
mixed to the consistency of cream. The last or setting coat consists of
a thin layer of slaked lime called plasterers’ putty. Some plaster of
Paris (gypsum) may be added, to ensure rapid setting, but it should
only be used in small quantities. For the internal plastering of rooms
_serapite_ (a form of cement) is now commonly employed. This is not so
absorbent as mortar, but is sufficiently so to prevent condensation
of moisture on the walls. Its chief advantage over plaster is that
it hardens quicker and is smoother, and can be used in a single thin
layer. This, however, diminishes the impermeability of ceilings for

Keene’s cement and Parian cement are mixtures of calcined gypsum and
other substances; Keene’s cement being the hardest, and capable of
receiving a high polish.

Selenitic cement contains a small proportion of plaster of Paris
ground along with lime. Lime may also be selenised by the addition
of any other sulphate, or of sulphuric acid. The presence of the
sulphate causes the lime to set rapidly. Selenitic cement is useful in
plastering, as a backing of cements, such as Parian.

The treatment of the =internal wall-surface= of a room differs
according to circumstances. =Lime-washing= is suitable only for
stables and other outbuildings. It is made by the addition of water
to quicklime, no size being added. It is an excellent germicide and
insecticide. =Whitewashing= is quite different from limewashing.
“Whiting,” _i.e._ finely-ground chalk, to which a certain proportion of
size and alum had been added is mixed with water. The size and alum are
added to prevent the whitewash from being rubbed off. =Distempering=
is identical with whitewashing, except that pigments are added. It is
distinguished from =painting in oils=, by the fact that the pigments
are mixed with size, instead of with linseed-oil and turpentine.
Painting in distemper is practically limited to plaster, which should
first receive a coat of whitewash to diminish its porosity. Oil-paints
are impervious, distemper is as absorbent as plaster or whitewash.
Various =washable distempers=, as duresco, are made, which are more
durable and non-absorbent. =Water-glass= consists of silicate of
potash, which in the gelatinous form is soluble like size in hot-water,
but when allowed to dry forms an impervious film. It can be used for
protecting porous stone from the effects of weather; and renders
internal surfaces of walls non-absorbent and washable.

=Oil-painting= renders wall-surfaces impervious, and enables them
to be easily washed. The importance of this in the event of any
infectious disease occurring, is obvious. The question arises whether
distempered or papered walls, which are porous, or painted walls,
which are non-porous, are preferable from the standpoint of health.
The difference between the two is seen during damp weather, when
moisture condenses and runs down the latter and is invisible in the
former. In practice in domestic dwellings the former are preferred;
but although some advantage is thus secured in ventilation through the
wall-substance, there is the serious disadvantage that particles of
dirt accumulate and may seriously interfere with the purity of the air
of a room. Hence the importance of rubbing down the internal surface of
a room, whether distempered or papered, at intervals with bread crumb
or dough (see page 332). This effectually removes all accumulations of
dirt. A painted wall presents the enormous advantage that it can be
frequently washed; while the loss of ventilation may be ignored, if
windows and doors be properly utilised for this purpose. The presence
of poisonous pigments in oil-paints is of importance to the workman,
but not to the householder except during the painting, as paint, unlike
distemper, does not rub off the wall. Lead is the chief poison present,
as white lead (carbonate of lead). Various substitutes for lead paints
have been introduced.

Painting wood or iron-work is valuable, not only as a preservative from
the effects of the weather and the oxidising action of the air, but
also because it tends, to a large extent, to prevent the absorption of
organic matters; and its surface can be frequently cleansed.

=Paper= is the material most commonly employed for covering walls. It
is more absorbent and retentive of moisture than distemper.

Light-coloured papers should be chosen, as they are more cheerful,
and are not so likely to harbour dust. Glaring patterns are
objectionable, as they tire the eyes. The paper should not present any
surface-projection for the lodgment of dust.

In bathrooms and water-closets, the wall-surface should be
non-absorbent. Paper, unless varnished, should therefore be avoided.
The best covering for these places is glazed tiling, or painted cement.

Not uncommonly, a new paper is pasted over an old one; and this may
be repeated several times. Under these circumstances dangerous dirt
accumulates. Before new papering is put on, the walls should be cleared
of all vestiges of the old, thoroughly washed down, and subsequently
coated with size (that is, “clear coloured”). The sizing diminishes the
absorptive power of the wall, and gives a good surface for applying the

Bed-room papers require to be more frequently changed than those of
other rooms. Bed-rooms in regular use should be re-papered at least
every two years. It is still better to use distemper for such rooms,
as this can be washed off in a few hours with comparatively little
expense, and can be made of any tint desired.

Rooms in the basement should not be papered, as the walls require
frequent washing down and cleaning. Here also a washable distemper
colour can be used.

Various kinds of sanitary paper are now sold which are washable, and
relatively non-absorbent. Some of them require varnishing; others do
not. Such papers are certainly cleaner than ordinary paper; but it
would not be safe to trust to their non-absorptive character. Lincrusta
Walton is non-absorbent, and can be scrubbed with soap and water; but
it is expensive. Other cheaper materials possessing the same properties
can now be bought.

=Arsenic in Wall-Papers and Paints= has until a few years ago been a
not uncommon source of prolonged ill-health—the cause of which has
possibly not been detected until the illness disappears, when the
offending room is vacated for a period. Arsenical pigments are now
only rarely used for wall-papers. The symptoms produced vary greatly,
and may closely simulate those of different diseases. In some cases
repeated attacks of diarrhœa and abdominal pain occur. Or there may
be nausea, headache, frequent griping pains, and loss of appetite.
In other cases restlessness, loss of sleep, and general malaise are
the chief symptoms, with the occasional addition of conjunctivitis
(superficial inflammation of the eye). Out of 100 cases collected and
reported on by a Committee of the Medical Society of London, diarrhœa,
nausea, and intestinal mischief occurred in 85; severe depression in
16; conjunctivitis in 19; and cough, asthma, etc., in 9.

The severity of the symptoms produced will vary with the amount of
arsenic contained in the paper, and the length of time daily that the
patient is exposed to the fumes.

Some persons again are much less susceptible to the influence of
arsenic than others. This will explain why some escape while occupying
the same room in which others suffer severely. More commonly, however,
the exemption is due to shorter exposure.

The most dangerous preparation occasionally employed in wall paper
printing is Scheele’s green (arsenite of copper). Emerald-green—an
aceto-arsenite of copper—is sometimes used to produce more delicate
tints. Aniline dyes, especially the red, may contain much arsenious
acid (white arsenic). The arsenic compound is made to adhere to the
paper by size or some other material. When dry, it cracks and peels
off, and minute particles get into the air as dust. In addition,
arsenic compounds easily volatilise, and become diffused in a
gaseous condition throughout the atmosphere of a room, even when its
temperature is not greatly raised. The virulence of the arsenical
colouring is in proportion to its volatility. Arsenic seems to be
much more dangerous when associated with size. It has been shown
that a mixture of white arsenic and starch paste, or other organic
substance, leads to the formation of gaseous arseniuretted hydrogen,
while this does not occur when no organic matter is present (Dr.
Fleck). Distemper frequently contains arsenic, and as it also contains
size, arseniurretted hydrogen is liable to be given off at any time.
Size is largely used for fixing colour; thus, the proper conditions
for the development of arseniurretted hydrogen—the most dangerous
compound of arsenic—are present. As much as 17 grains of arsenic have
been discovered in each square foot of a wall-paper. Now, arsenic is
sometimes given internally for certain skin and other diseases, but the
dose is only from 1∕60 to 1∕12 grain; the capacity for poisoning of
such a paper as the above will therefore be evident.

Papers of other colours than green have been found to contain
dangerous quantities of arsenic; thus blue, mauve, red, and brown
may contain large quantities; the delicate greys often yield a
considerable amount, and some white papers are heavily loaded with
it. Arsenic is occasionally present in stockings and other wearing
apparel, artificial flowers, toys, etc. In these cases, it may produce
irritation of the skin, and even eczema.

The presence of =arsenic may be detected= by the following tests:—

 (_a_) _Reinsch’s test._ A portion of the suspected paper (two or three
 inches square) is cut into small pieces, and placed in a good-sized
 test tube; water is added until the tube is about a third full and
 then one or two teaspoonfuls of pure hydrochloric acid, and a small
 piece of pure copper foil. If the test tube is now heated for a few
 minutes over a spirit lamp, arsenic, if present, will be deposited as
 a black or dark steel-coloured coating on the copper. A mere tarnish
 of the copper must not be accepted as evidence of the presence of
 arsenic, but an almost complete obliteration of the colour of the

 (_b_) Take the copper covered with arsenic, dry it, and then heat it
 in a perfectly dry test tube. Crystals of white arsenic, which may be
 identified under the microscope, will be deposited higher up in the

 (_c_) _Marsh’s test._ The ordinary apparatus for developing hydrogen
 by the action of diluted sulphuric acid on zinc is employed, the
 suspected paper being inserted in the bottle. The hydrogen coming off
 is burnt, and a clean porcelain surface is applied to the flame. If
 there is arsenic in it, it is deposited on the porcelain in a black

=Windows= are required to open directly into the external air in every
habitable room. The window area according to the model bye-laws of the
Local Government Board and the London Buildings Act of 1894, must be at
least one-tenth of the floor area, and half of this at least must be
made to open. The following rules have also been given. (B = breadth, L
= length and H = height of room.)

  _Area of window_
      (B × L)/10         _London Building Act_

      (B × L × H)/100    _Gwilt_

      √(B × L × H)       _Morris_

In a room measuring 15 × 20 × 12 feet, the preceding rules would give
a superficial area of window space of 30, 36, and 60 square feet
respectively. Plate glass dissipates heat less quickly than sheet glass.

Objection may be taken to plate glass windows, in passing, especially
for shops, banks, etc., in view of the fact that they are commonly made
without any arrangement for ventilation (see also page 148).

The hygienic necessities of =Floors= are that they shall be impervious
to moisture and to dust. On the =ground floor= the ordinary arrangement
is to provide a joisted and boarded floor raised about a foot above the
ground. Dry rot is one of the dangers in connection with such =boarded
floors= on the ground floor. The chief causes which tend to induce
rotting, are damp walls, lack of ventilation, contact with mortar, damp
earth, or vegetable mould, and worst of all, alternations of damp and
dryness, or wet along with heat.

In order to avoid these dangers in connection with boarded floors, the
ends of all timbers resting on walls should have a clear air-space
around them, and communicate with the external air by means of
perforated bricks. The larger timbers, girders, etc., should rest
on stone templates, and the smaller joists on hoop-iron bonds. In
all cases, the timber used should be well seasoned, and properly
ventilated. The ends of oak posts, which are to be driven into the
ground, should be charred, if the timber is old, or steeped in a
solution of chloride of zinc.

The ends of the joists should be trimmed, so as not to come too near to
chimney flues.

The best plan for flooring is to place an impervious flooring resting
on the solid ground. This is more secure against rot than the boarded
floor, and affords no space for dirt and vermin to lodge. Such an
impervious floor may be formed of concrete over a layer of asphalte,
as in the well-known terrazzo flooring. This is very suitable for
corridors, pantries, etc. For living-rooms =wood-block flooring= is
placed over the cement, molten pitch connecting the two. The blocks
are 2 to 3 inches thick. If the wood is soft, as deal, it must be kept
clean by washing; if hard, as oak or teak, it can be wax-polished.
_Parquetry_ consists of small pieces of hard woods carefully fixed and

For =upper floors= the ordinary flooring is of floor-boards supported
on wood joists, beneath which are wood laths and plaster. The
floor-boards should be thoroughly seasoned, otherwise they will shrink,
and the joints be filled with dirt. This dirt may accumulate for years
between the floor and the ceiling of the room below, vitiating the air
and helping to increase the stuffiness characteristic of dirty houses.
Various plans are adopted for uniting the edges of floor-boards and
preventing dust from dropping between the boards.

[Illustration: FIG. 41.


The one most commonly employed is the _ploughed and tongued floor_
(Fig. 41). In this, both edges of the floor are grooved so as to
receive strips or tongues of iron or wood, an equal half of each strip
being in the groove of each of two boards when they are in place.
A less expensive method than the above is to _splay_ the ends of
the boards so that they slightly overlap each other. This is not so
efficient as the above, but is much better than simply placing the
boards side to side as is commonly done.

_Solid wood floors_ resting on a bed of concrete are free from the risk
of harbouring dust, and are relatively fire-proof.

Oak or teak in narrow boards, made with close joints, and then
oiled and beeswaxed and rubbed to a polish, makes a good and almost
non-absorptive floor. One of the best floors is made of concrete, with
iron joists, and oak boards laid above this.

=Carpets= are commonly made to cover the entire floor of rooms. This
cannot be too much deprecated. Carpets, like curtains, are mere
dirt-traps, which become loaded with filth of every description. This
is abundantly proved when a carpet is swept, and the dust allowed to
settle on all the articles in the room. Such dust, if examined, will
be found to consist not only of mineral matter, but also of every
description of vegetable and animal impurities. The inhalation of such
dust, which may contain particles of fæcal matter, as well as the dried
expectoration from consumptive or other infectious patients, is a not
infrequent cause of infection to healthy persons.

The substitution of a central carpet, for one covering the entire
floor, is a great improvement.

The carpet should be easily removable, in order that it and the floor
may be thoroughly cleaned at intervals.

In bedrooms, the less carpet the better. Good Chinese or Indian
matting is serviceable, as it does not retain the dust and other
impurities which are apt to become fixed in the woolly texture of the
carpet. Oil-cloth, linoleum, and similar materials are in common use
for covering halls, passages, etc. They are particularly useful in
preventing dust from gaining access to the spaces between floor-boards.

The =prevention of dust= should be the great aim of the householder,
as dirt frequently carries infection. =Sweeping= as ordinarily done
scatters dirt over the room, and =dusting= with a dry cloth fails to
remove it. Mechanical sweepers, in which the dirt is collected in a
box are valuable. The best plan is to have movable carpets, roll them
up for shaking or beating at a distance from any house, and wipe the
boards with damp cloths. All wooden and leather furniture, picture
frames, etc., should be wiped down with cloths rung out of water so as
to be just damp.



=The Varieties of Soil.=—The following facts summarise what is
regarded as the relative healthiness of various sites for dwellings.
The differences between different sites may, however, be reduced to
a minimum by having the dwelling well above the ground-level and by
protecting it from dampness.

1. =Granitic=, =Metamorphic=, and =Trap Rocks= usually form healthy
sites for houses. The slope is generally great, and the ground
consequently dry.

2. =Clay Slate= resembles the last in its effects on health. Water is,
however, often scarce, owing to the impermeability of the rocks, and
for the same reason occasional floods occur.

3. =Limestone= and =Magnesian Limestone Rocks= resemble the last in
possessing considerable slope, so that the water passes away quickly.
The hard oolite is the best formation under this head, and magnesian
limestone the worst.

4. =Chalk= is a healthy soil when unmixed with clay, and permeable.
Goitre is not so common as in limestone districts. If the chalk be
mixed with clay, it is often damp and cold.

5. =The Sandstones= are healthy, soil and air being dry. If mixed with
clay, or if clay lie under a shallow layer of sand-rock, the site may
be damp. The hard millstone grit is a healthy formation.

6. =Gravels= of any depth are healthy, unless they are water-logged, as
near rivers. Then a house on impervious clay may be drier than one on

7. =Sands= are healthy when of considerable depth; they may be
unhealthy when shallow, and lying on a clay basis; or when the ground
water rises through them from ground at a higher level.

8. =Clay=, =Dense Marls=, and =Alluvial Soils generally=, are apt to
be cold and damp. Water is retained in them, and is often very impure.
Thorough drainage improves a clay soil, and a house on a clay soil may
be so constructed, as not to be damp.

9. =Cultivated Soils= are not necessarily unhealthy; but

10. =Made Soils= are always to be carefully avoided, as sites for
houses. The materials with which inequalities have been filled up are
commonly the contents of dust-bins, or some other refuse. The gradual
putrefaction of organic matters renders the air about the houses
impure. Such soils require free subsoil drainage, in order to keep
them dry. It appears that the organic matters in soil are gradually
removed by oxidation and bacterial purification. At least three years
should be allowed before any such site is built on.

The following table places different geological formations in their
order of healthiness for the purposes of a site (Parkes):—

  │                                          │PERMEABILITY│ EMANATIONS  │
  │                                          │ OF  WATER. │  INTO AIR.  │
  │1. _Primitive rocks, clay slate, millstone│            │             │
  │     grit_                                │  Slight.   │    None.    │
  │2. _Gravel and loose sands, with permeable│            │             │
  │     subsoils_                            │  Great.    │   Slight.   │
  │3. _Sandstones_                           │ Variable.  │   Slight.   │
  │4. _Limestones_                           │ Moderate.  │     ──      │
  │5. _Sands with impermeable subsoil        │Arrested by │Considerable.│
  │                                          │ subsoils.  │             │
  │6. _Clays, marls, alluvial soils_         │  Slight.   │Considerable.│
  │7. _Marshes, when not peaty_              │  Slight.   │Considerable.│

The general geological conditions have an important bearing on the
choice of a site for a house in so far as they affect the local
climate, and the difficulty of keeping the house warm and dry.
Pettenkofer expressed this in his dictum, that we take holiday for
change of soil, rather than for change of air. The character of a soil
has an important influence on humidity, radiation, evaporation, and
in fact most of the factors going to make up “climate.” The immediate
local surroundings of a house (page 201) have an even greater influence
on its salubrity than the underlying geological formation.

The soil consists of mineral and organic matters. On the amount and
character of the animal and vegetable matters (along with the condition
of moisture and aeration), the healthiness of a given soil depends.
The presence of vegetable matter, subject to alternate wettings and
dryings, and to heat, has until recently been regarded as the condition
on which malaria depends; but it is now known that malarial places
owe their character to their being favourable to the growth of the
larvæ of certain mosquitoes (page 307); and that drainage of the soil
cures malaria by removing the ponds in which these develop. The two
chief agencies at work to rid the soil of organic impurities, are
nitrification and the influence of growing plants. The organic matters
become oxidised into ammonia, nitrites, and nitrates, and these are
eagerly assimilated by vegetation.

=Nitrification= is effected by micro-organisms in the soil. Ordinary
garden mould and agricultural humus contain large numbers of
micro-organisms. Their number diminishes with the depth of the soil,
and below 12 to 15 feet there are few. Apart from the occasional
presence of pathogenic (disease-producing) micro-organisms, the most
important are those producing oxidation of organic matter, especially
_nitrification_. This occurs at a less depth than 4 feet from the
surface of the ground. The operation of these micro-organisms is
necessary to convert sewage and other impurities into harmless
nitrites and nitrates, and it is regularly going on in all normal
soils. That the power of purification of sewage by soil is due to the
micro-organisms in the latter, can be proved by the fact that when the
soil is baked, it loses for a time its purifying power.

=The Air contained in the Soil= varies greatly in amount with the
character of the soil, and with the level of the ground-water. As
the ground-water rises, the ground-air is driven out. Thus, after
a heavy rainfall a large proportion of this air will be displaced.
Variations in barometric pressure, and a rise or fall of temperature,
cause movements in ground-air. A house artificially warmed is liable
to receive air from underground, unless means are adopted to make
the floors impervious. The warmth of the house acts as an air-pump,
aspirating the colder air into its interior. The air from cesspools or
defective drains may be similarly aspirated into the house; and the
same cause particularly explains the unhealthiness of houses built on
“made soils”. Coal gas has occasionally made its way into houses when
not laid on to them, by the gas escaping from leaky pipes in the street
often following the track of water or drain-pipes until it is aspirated
from beneath the house into its interior. This has resulted in one
instance in an explosion, and in others in poisoning by the gas.

[Illustration: FIG. 42.]

The occurrence of currents of air in soil may be illustrated by a
simple experiment. In Fig. 42 B is filled with fine sand in which is
imbedded the tube A with its open end F at the bottom of the sand
C. The upper end of A is connected by the rubber tubing D with the
U-shaped tube E, in which is inserted some coloured water. When the
experimenter blows on the surface of the sand at A, the impulse passes
through the sand up the tube from F, and deflects the water in the
syphon bend at E.

The _amount_ of ground-air varies greatly. Loose sands often contain
40 to 50 per cent., soft sandstone 20 to 40 per cent., and loose
surface-soil many times its own volume.

The _nature_ of the air is not accurately known. It is, however,
extremely rich in carbonic acid, of which it contains from 1 to 10 per
cent. or even more. The carbonic acid is derived from the organic
matter in the soil, by the action of bacteria, in a manner analogous to

=The Water contained in the Soil= is divided into moisture and ground
or subsoil-water. When air is present in the soil as well as water,
the soil is merely moist. Pettenkofer defines the ground-water as that
condition in which all the interstices are filled with water, so that,
except in so far as its particles are separated by solid portions of
soil, there is a continuous sheet of water.

The =Moisture= in the soil varies in amount. Open gravel will absorb
from 9 to 13 per cent. by weight of water; gravelly surface soil 48
per cent.; light sandy soils from 23 to 36 per cent.; loamy soil 43
per cent.; stiff land and clay soils from 43·3 to 57·6 per cent.;
sandy and peaty soils from 61·5 to 80 per cent.; peat 103 per cent.
(B. Latham). The moisture being derived from the rainfall on one side,
and the ground-water on the other, will vary with the amount of these.
Some soils are practically _impermeable_ to water, such as trap or
metamorphic rocks, unweathered granite, hard limestone, and dense
clay; while others, such as chalk, sand, sandstone, vegetable soils
are _permeable_. Commonly the metamorphic rocks and hard limestones
present fissures, which render them pervious. The rainfall which does
not penetrate the soil flows into the streams and rivers at once, or
is re-evaporated. The amount of _percolation_ of rainfall is estimated
by an artificial soil-gauge. Most percolation and least evaporation of
rainfall occurs from October to March inclusive. The difference between
the percolation and rainfall is the loss caused by evaporation and

The =Ground-water= forms a subterranean sheet of water, which is in
constant motion. There is first of all, an irregular rise and fall of
the water, according as it receives new additions from the rainfall, or
loses a certain amount of its substance by percolation and evaporation;
and there is, secondly, a constant movement towards the nearest
water-course or the sea. Many towns derive their drinking-water from
the ground-water, especially that in the chalk. Thus in Brighton there
are no streams; but wells are dug in the South Downs about 150 to 180
feet deep down to the level of the subterranean water. Then long adits
are tunnelled, parallel to the coast at or near the level of this
water, which is thus intercepted on its way towards the sea, and pumped
up to supply the town. In Munich, Pettenkofer reckoned the rate of
movement of the ground water towards the outlet as 15 feet daily. It is
impeded by impermeability, or a deficient slope of the soil. The roots
of trees also greatly impede its flow.

_The level of the ground-water_ is constantly changing (see Fig. 7).
The alteration in level may be only a few inches either way, while in
some parts of India it is as much as 16 feet. The level is generally
lowest in October and November, highest in February and March.

A _fall_ in the level of the ground-water may be due to a dry season,
or to improved subsoil drainage. A _rise_ in its level is due to
an increase in the rainfall, or some obstruction in the outflow,
as from a swollen river. The tide may influence the level of the
ground-water at a great distance. A sudden alteration in the level of
the ground-water is a common cause of floods in mines.

The distance of the ground-water from the surface may be only two or
three feet, or several hundred feet, the difference being due to the
varying level of the nearest impervious stratum of soil. Its distance
below the surface of the soil can easily be measured by ascertaining
that of the water of a shallow well in the neighbourhood. It should
preferably not be nearer the surface than five or six feet. Sudden
changes in the level of the ground-water from inundations render any
soil unhealthy, and are even more objectionable than a persistently
high level. This is especially true in the case of permeable soils.
A sudden rising of ground-water expels the air in the soil, together
possibly with particles which may comprise infectious material; it also
washes similar impurities out of the subsoil, and carries them into
neighbouring wells. Numerous epidemics have been traced to this source.

=The Temperature of the Soil= varies greatly with its geological
character, as well as with the temperature of the atmosphere. The
daily changes in the temperature of the atmosphere do not affect the
soil beyond a depth of about three feet. The annual changes in the
atmosphere will affect the soil in a varying degree, the amount being
dependent on the character of the soil as regards conductivity and
retentiveness for heat. Such annual variations do not penetrate below
forty feet, and are very small below twenty-four feet. The temperature
of the earth increases with its depth, the rate of increase in England
being stated to be about 1° Fahr. for every 54½ feet.

In England the water of permanent springs has a fairly constant
temperature of 49° to 51° Fahr., which is the temperature of the deeper
part of the subsoil. The method of taking the daily temperature of the
subsoil at a depth of 4 feet is described on page 240.

Although the average temperature of any soil depends on the climate,
soils conduct heat in a very varying degree, and therefore absorb
unequal quantities. This has an important bearing on the comfort of
those living on a particular soil. Schübler’s experiments give the
absorbing power of the chief kinds of soil, 100 being taken as the

  │ _Sand, with some lime_  100·0 │
  │ _Pure sand_              95·6 │
  │ _Light clay_             76·9 │
  │ _Gypsum_                 73·2 │
  │ _Heavy clay_             71·1 │
  │ _Clayey earth_           68·4 │
  │ _Pure clay_              66·7 │
  │ _Fine chalk_             61·8 │
  │ _Humus_                  49·0 │

It is evident from this table that sand is very retentive of heat,
while clays and humus are very cold. Green vegetation lessens the
absorbing power of the soil, and radiation of heat is more rapid,
evaporation occurring constantly from the herbage. The influence of
trees on the temperature of the soil is considered on page 228.

Damp soils are colder than dry soils because of the evaporation going
on. Buchan finds as the result of drainage of the soil, that (1) the
mean temperature of arable land is raised 0·8° Fahr.; (2) cold is
propagated more quickly through undrained land; (3) drained land loses
less heat by evaporation; (4) the temperature of drained land is more
equable, and (5) in summer is often 1·5° to 3° above that of undrained

DISEASES ARISING FROM THE SOIL.—The soil may be a cause of disease:
(_a_) indirectly and (_b_) directly.

_Indirectly_ a damp soil may cause disease by acting as a means of
lowering the vitality of man and diminishing his resistance to disease.
It is in this way that it has been credited with causing such diseases
as neuralgia, catarrhs, and rheumatism. It is one of the elements in
producing a climate unfavourable to health. As to rheumatism, see page

_Directly_ the soil may transmit the actual contagia (micro-organisms)
of disease either by means of the subsoil water or its air. In the
former case the disease-causing material gains access to the drinking
water of wells, springs, or rivers; in the latter case it may be borne
to the surface of the soil by currents of the ground-air or by insects,
and then inhaled as dust, or gain access to food.

Certain disease-producing micro-organisms have been proved to be
capable of living for some time in the soil. The chief of these found
in the soil are the bacilli of tetanus (lockjaw), of anthrax, of
malignant oedema, and of enteric (typhoid) fever. There are reasons for
thinking also that the micro-organisms causing diphtheria, rheumatic
fever, and epidemic diarrhœa, and possibly some other diseases, may
occasionally live in the soil. In some diseases as enteric fever,
cholera, dysentery and anthrax, the contamination of the soil can be
shown to be derived from a patient suffering from the same diseases.
In others, and particularly in tetanus, the same chain of evidence is

(1) The conditions favourable to the production of =malarial diseases=
have been generally considered to be the presence of a certain
proportion of dead organic matter, the exposure of the soil to
alternations of heat and moisture, with a limited access of air, and a
temperature of at least 65°F. Though most common in marshy districts,
and in recent alluvial soils, malaria may develop in connection with
any geological formation. That it may be removed by drainage of the
subsoil, is well known. The true nature of the connection between soil
and malaria is stated on page 220.

(2) According to observations made by Pettenkofer in Munich, attacks
of =enteric (typhoid) fever= are connected with fluctuations of the
subsoil-water. He states his conclusions as follows:—

 “Between the fluctuations of subsoil water and the amount and severity
 of enteric fever there is an unmistakable connection in this wise,
 that the total number of cases of and deaths from enteric fever falls
 with a rise of the subsoil water, and rises with fall of it; that
 the level reached by the disease is not in proportion, however, to
 the then level of the subsoil water, but only to the variation in it
 on each occasion; or in other words, that it is not the high or low
 level of the subsoil water that is decisive, but only the range of

His observations have not been confirmed in this country; and the
coincidence between excess of enteric fever and lowness of ground-water
has been explained by the fact that under these circumstances the water
in wells is low, and the area of drainage and the consequent risk of
contamination are proportionately increased. There can be no doubt
that the most common origin of enteric fever is from the infection of
water or milk by infective matter from a recent case of the disease.
This does not exclude the fact that enteric fever in this country is
more prevalent in hot dry autumns, in which the ground-water is low.
Probably under such conditions the contagium of the disease multiples
more rapidly in the soil, in privies and other polluted places, and
consequently the risks of infection of water and food as well of
infection by dust carried from the contaminated spot are greatly

(3) In regard to =cholera=, Pettenkofer holds similar views. He
believes that the contagium of cholera can only be developed when
there is a damp porous subsoil to receive the infected stools from a
cholera patient; the damp porous subsoil forming a second host in which
the poison of cholera must pass through one stage of its existence,
before it is again capable of producing the disease. Such an essential
relationship of the soil is not borne out by observations in India; and
in England cholera has been repeatedly shown to be due to contamination
of food (_e.g._ oysters) or water by the stools of preceding cholera
patients, without the intervention of any agency of the soil.

(4) It has been repeatedly stated that a damp soil favours the
prevalence of =diphtheria=. I have shown elsewhere, however, that
this is not true, and that the greatest epidemics of diphtheria have
occurred in exceptionally dry years, especially when several years
of exceptionally small rainfall have succeeded each other; and have
suggested that this may be associated with an intermediate stage
in the life-history of the diphtheria-bacillus in the soil. A low
ground-water and a comparatively high temperature of the soil go along
with deficient rainfall, and would probably favour the multiplication
of this bacillus in the soil.

(5) In =rheumatic fever= I have similarly shown that the supposed
connection between damp soil and this disease is erroneous, the disease
being most prevalent, both in this and other countries, in years of
exceptional drought.

(6) =Epidemic or Summer Diarrhœa= has been supposed to have a special
relationship with soil-temperature, Ballard having found that the
summer rise in the mortality from this disease does not commence until
the mean temperature recorded by the four-foot earth thermometer has
attained somewhere about 56°F. The soil-temperature may be accepted as
a convenient index of the conditions causing this disease. The disease
I have elsewhere shown occurs most severely with a high temperature
of the air and a deficient rainfall, and its fundamental cause is an
unclean soil, the particulate poison from which infects the air, and is
swallowed most commonly with food, especially milk.

(7) The close connection of =consumption= (phthisis) with a damp soil
has been independently stated by Drs. Buchanan and Bowditch. Buchanan
found that in the districts where improved sanitary arrangements had
led to a drying of the soil, the death-rate from phthisis diminished;
but where with sanitary improvements the soil was not dried, the
death-rate from phthisis remained in one or two instances almost
stationary. In Salisbury, Ely, Rugby, and Banbury, the death-rate from
phthisis fell from 141 to 49 per cent. The amount of reduction in the
death-rate from phthisis did not appear to be consistently proportional
to the amount of drying of the subsoil. In a later investigation into
the incidence of deaths from phthisis in the south-east of England,
Buchanan came to the further conclusions that (_a_) there was less
phthisis among populations living on pervious soils than among
populations living in impervious soils; (_b_) less phthisis among
populations living on high-lying pervious soils than among populations
living on low-lying pervious soils; and (_c_) less phthisis among
populations living on sloping impervious soils than among populations
living on flat impervious soils. He, therefore, concluded that _wetness
of soil is a cause of phthisis to the population living upon it_. (See
also page 313).

=Drainage of the Soil.=—There are two chief plans for rendering the
soil drier—deep drainage and opening the outflow.

=Subsoil Drainage= should always be carried out by drains, separate
from those for sewage. If the sewers are utilised for this purpose,
their contents when full contaminate the surrounding soil. The subsoil
drains should be composed of agricultural, _i.e._ unglazed, drain-pipes
laid in towns in the same trench, but above the sewers, and they should
discharge into the nearest water-course. If it is necessary to join
them with a sewer, they should not pass directly into it, but into a
disconnecting man-hole.

=Opening the Outflow=, in order that water may not remain stagnant
in the soil, is occasionally required. This may be done by clearing
water-courses, removing obstructions, and forming fresh channels.

The provision of sufficient =surface-drains= to carry off ordinary
water and storm-water helps in drying the soil of urban districts.

=Vegetation= tends to diminish dampness of soil by causing rapid
evaporation, and at the same time uses up the organic matter in the
soil. Certain plants are more active in producing these effects than
others: the _Eucalyptus_ genus, including many species, and represented
by the well-known _blue-gum tree_ of Australia, is noted for its power
in this respect; and the common sun-flower, which is very easy of
cultivation, has a powerful influence in the same direction.



=The Climate= of a country has an important influence on the health and
character of its inhabitants. The character of a climate depends on
four main conditions:—

  1. The distance from the equator.
  2. The height above the sea.
  3. The distance from the sea.
  4. The prevailing winds.

There are other conditions which are of subsidiary importance, but
which have great influence in modifying the climate of any given
locality. Thus:—

5. The nature of a surface—its aspect, shelter, slope; the colour of
the soil or rock, the reflection from rocks or sheets of water, and the
influence of vegetation.

6. The cultivation of the soil.

7. The drainage of marshes and damp soils.

8. The planting and clearing away of forests.

=The Distance from the Equator= is the most important factor in
relation to climate. The sun’s rays become less powerful as they fall
more obliquely, in travelling from the equator. This primary factor
in producing climate is largely modified, however, by the relative
distribution of land and water, and by the character of the prevailing
winds of a district.

=The Elevation= of a locality affects the temperature and the
barometric pressure, both falling as the height is increased. The
amount of fall varies with the latitude of the place, with its
situation in regard to surrounding districts, the degree of moisture of
the air, the presence of winds, the hour of day, and the season of the
year. It is usual to allow 1° Fahr. for every 300 feet of ascent above
the level of the sea, and one-thousandth part of an inch depression of
the barometer for every increase of one foot in height.

=Hills, Plain and Valley.=—The law of decrease of temperature
with increase of altitude, is liable to great modifications, and
even subversions, from various causes. The chief cause producing
such modification of the law is the _elevation in relation to the
surrounding district_. Thus, in the case of rising ground, the higher
parts become rapidly cooled by radiation. The air here is likewise
cooled by contact, and becoming heavier in consequence, flows down
to low-lying ground. Hence places on rising ground are not so fully
exposed to the intensity of frosts at night as places in the valley.

Valleys surrounded by hills and high grounds, not only retain their own
cold and heavy air, but serve as reservoirs for the cold air falling
from neighbouring heights. One finds, in consequence, mists in low
situations, while adjoining eminences are quite clear.

The =air of mountains= is (1) cooler than that of lower districts
with the exception already named. (2) It is less dense in proportion
to the altitude; its pressure at the height of 16,000 feet being only
half that at the sea level. (3) Its absolute humidity is decidedly
diminished; there is some difference of opinion as to the relative
humidity. (4) The air is as a rule purer. It is generally free from
dust, and to a large extent aseptic (that is, free from microbes).
(5) The amount of ozone is commonly greater than in lower regions. In
addition to these characters, (6) the light is intense, and (7) the
direct heat of the sun is greater, and the difference between sun and
shade greater than in lower regions.

Owing to these peculiarities of mountain air, it is of great value
as a restorative. The circulation of blood is increased, nutrition
is improved, the chest expands, and the increase in its size may be

The presence of =forests and sheets of water= counteracts the effects
of radiation from the earth. Thus if a deep lake fills the basin of a
valley, the cold air descending from higher levels cools the surface
water, which sinks and is replaced by warmer water from below. In this
way deep lakes are sources of heat in winter, and places on their
shores are free from the severe frosts which are peculiar to other
low-lying situations.

If the slopes of a hill are covered with trees the temperature of its
sides and base are considerably increased, as the trees obstruct the
descending currents of cold air. The frosts of winter are felt most
severely in localities where the slopes above them are destitute of
vegetation, and especially of trees. It follows that in any given
locality, the best protection against the winter cold is ensured by
a dwelling situated on a slope a little above the plain or valley
from which it rises, with a southern exposure, and sheltered by trees
planted above it. Such local conditions should always be carefully
enquired into, when a choice of site is possible, as the temperature of
one part of a neighbourhood may differ by several degrees from that of
another part near at hand. This is particularly important in the case
of invalids.

=Forests= tend to modify a climate, and mitigate its extremes, whether
situated on the slopes of mountains or on plains. In America, as
elsewhere, the effect of destruction of forests has been to produce
greater variation in the annual rainfall, to lengthen periods of
drought, and to increase the power of floods and cloud bursts. Trees
are heated and cooled by radiation like other bodies, but from their
slow conducting power, the periods of their maximum and minimum
temperatures are not reached for some hours after the same phases of
the temperature of the air, and the effects of radiation are not
confined to a small surface on the soil, but distributed to the level
of the tree-tops. For these reasons, trees make night warmer and day
cooler, thus giving to forest districts something of the character
of an island climate. Evaporation occurs slowly from the damp soil
beneath trees, as it is screened from the sun, and the trees prevent a
free circulation of wind. Hence the relative humidity and rainfall are
increased. At the same time forests mitigate the disintegrating effect
of the rainfall on the soil.

=Ground covered with Vegetation= has a more uniform temperature than
bare soil, the effect being much the same as that of forests, though on
a smaller scale.

All growing vegetation evaporates a large quantity of water. A plant
evaporates 200 pounds of water while it forms one pound of woody fibre;
the effect of a forest must, therefore, be enormous. At the same time,
vegetation, and especially trees, retain moisture in the soil. The
water-supply of barren regions may be greatly increased by planting

_The absence of vegetation_ leads to extreme fluctuations of
temperature. An extent of sand, for instance, raises the temperature of
the air greatly during the day, as it is a bad conductor; but at night,
radiation is very great, and the temperature falls accordingly.

=Relation of Sea to Climate.=—Water has the greatest specific heat of
any known substance, being four times greater than that of the earth’s
crust. On this account it takes longer to heat and to cool than the
earth. Unlike the earth, likewise, it allows free penetration of the
sun’s rays,—in clear water probably to a depth of at least 600 feet;
consequently, the surface of the water becomes less rapidly heated.
The freezing point of fresh water is 32°, while that of sea-water is
27·5°-28·4°. Thus, the sea remains open at a temperature at which
inland lakes freeze, and has, therefore, a greater influence in
moderating winter cold and summer heat. Another factor rendering it
more competent to mitigate extremes of temperature than lakes, is the
presence of currents, causing admixture of the water of different
climates. Of these currents the most important for this country is the
Gulf Stream, an immense stream of water which, when it leaves the Gulf
of Mexico, is travelling at the rate of four to five miles an hour, and
has a surface temperature of 88° F.

It is important to distinguish between the _surface_ temperature and
the _deep-sea_ temperature, the latter being fairly constant. The
whole of the depths of the sea is filled with water at or near 32°
Fahr., which in the tropics is 40°-50° below the temperature of the

The influence of seas on climate is so great as to lead to a
classification of climates into oceanic, insular, and continental.

An =oceanic climate= is least liable to violent changes of temperature.
It can only be obtained by a sea-voyage.

An =insular climate= presents smaller differences between the
temperature of summer and winter than the interior of great continents,
especially when the island is small and in the midst of the ocean. In
the British Islands, the prevailing winds being westerly, places on
the east coast are less truly insular than similarly situated ones on
the west coast; and their climate approaches more nearly that of inland

A =continental climate= is drier and more subject to extreme
alternations of temperature than insular and oceanic climates.

=Isothermal lines= (lines of equal mean temperature) around the world
bend up and down, the bendings being determined by the relative
position of continents and oceans. New York has the same mean
temperature as London, though New York is as far south of London as
Madrid. This fact illustrates the fallacy in judging of the climate
of a locality by the annual mean temperature. Means, it has been well
said, are general truths but particular fallacies. One should know the
extremes of temperature, and the extremes for each month of the year,
as well as the amount and distribution of the rainfall, and the amount
of sunshine, before judging of a local climate.

=Winds= are due to differences in atmospheric pressure caused by
changes in temperature and moisture. Inasmuch as the temperature
and degree of moisture of air vary with the prevailing winds, their
consideration becomes very important. Winds bring with them the
temperature of the air they have traversed: thus, in England, south
winds are warm, while north winds are cold. Winds coming over an ocean
cause less variation in temperature than those which have passed over
an extensive tract of country. Thus, moist ocean winds are accompanied
by a mild winter and cool summer, while dry continental winds cause the
reverse conditions. The amount of moisture capable of being carried by
a current of air increases with its temperature; therefore, equatorial
winds become moister as they proceed, while north winds become drier.
The south-west winds, in the British Isles, being both oceanic and
equatorial, are very moist, while the north-east winds, being both
northerly and continental, are peculiarly dry and parching.

Owing to the atmospheric pressure diminishing from the south of Europe
northwards to Iceland, south-west winds are the most prevalent in Great
Britain; and as this diminution of atmospheric pressure is greatest in
the winter months, south-west winds are most common at this season. The
result is that the temperature of these islands is higher than that
due to mere latitude, and the temperature on the west coast is fairly
uniform from Shetland to Wales.

_Mountain ranges_ have an important bearing in determining the
character of the prevailing winds. If the range is perpendicular to
the direction of the winds, the latter lose the greater part of their
moisture, and the places to leeward being exposed more completely to
solar and terrestrial radiation (from comparative absence of aqueous
vapour), winter becomes colder and summer hotter. The difference
between the climates of the west and east parts of Great Britain is
largely due to this cause. In Ireland, the mountains are not grouped
in ranges running north and south, but in isolated masses, and the
difference in climate between the east and west coasts is consequently
less marked.

The =prevailing winds= have a great =influence on the rainfall=.
(1) Thus if the wind has traversed a considerable extent of ocean,
the rainfall is moderately large. (2) If a wind reaches into a
colder region, its saturation point is lowered, and the rainfall is
greatly increased; and if a range of mountains lies across its path,
the rainfall on the side facing the wind is greatly increased, but
diminished on the opposite side of the range. (3) If a wind after
reaching land proceeds into lower latitudes or warmer regions, the
rainfall is small, or absent. This accounts for the rainless summers of
California, North Africa, and South Europe.

The =Barometric Pressure= varies daily, being at its maximum at about 9
a.m. and 9 p.m. The average range in the tropics amounts to 0·1 inch,
but in this country does not usually exceed 0·02 inches. During the
year the minimum barometric pressure usually occurs about the end of
October, while the maximum is usually at the end of May or early in
June. The ordinary variations in barometric pressure with changes of
weather have little apparent effect on health; but more extreme changes
produce marked effect. In mountain-climbing faintness and nausea may
be caused at great altitudes. At the opposite extreme, in pier-driving
and laying the foundations of bridges, men have to work in air-chambers
at a pressure of from three to four atmospheres. Then what is known as
“caisson disease” may be produced. The usual symptoms are discomfort or
pain in the ears, giddiness, bleeding at the nose, vomiting, or even
temporary paralysis. In such occupations it is most important that on
leaving the air-chambers the atmospheric pressure should be gradually

The use of the barometer as a weather indicator is based on the fact
that moist air is lighter than dry air. Hence, if the air is moist and
rain imminent, the barometer falls rapidly. The maximum daily range
in this country is rarely greater than 3 inches. Weather observations
can be based on records kept at one spot. Their value is greatly
enhanced, when such observations are compared with others distributed
over a wide area. The wider the area from which such observations are
collated, the more accurate the deductions that can be secured. If
observations of places at which the barometrical pressure is identical
be recorded on a map, we have a _synoptic map_, and the lines of equal
barometrical pressure connecting these points are called =isobars=.
The modern development of meteorology, enabling forecasts of weather
to be made with approximate accuracy, is based chiefly on telegraphic
communication of information, enabling isobars to be constructed.

It is found that =isobars= arrange themselves into seven chief forms
(1) Cyclones. (2) Secondary cyclones. (3) V-shaped depressions. (4)
Anti-cyclones. (5) Wedge-shaped isobars. (6) Cols. (7) Straight isobars.

Each of these varieties is shown in Fig. 43, which embraces the
conditions in Europe, the eastern part of the United States, and over
the North Atlantic on a certain day.

The closeness of the isobars, _i.e._ the rapidity of changes in
atmospheric pressure determines the _barometric gradient_. The steeper
this gradient, the greater the velocity of the wind in any given place.
The distance between two isobars is equal to a change of a tenth of an
inch in the mercury in the barometer. The direction of the wind in a
given place is from the higher to the lower isobars. This is expressed
in _Buys Ballot’s law_, which states that in the northern hemisphere,
if you stand with your back to the wind, the lowest pressure is to your
left and in front.

[Illustration: FIG. 43.


=Cyclones= or depressions are areas of low barometric pressure. A
cyclonic system (Fig. 43) is formed by circles of concentric isobars.
The differences between cyclones and anti-cyclones are as follows:—

            _Cyclones._               │        _Anti-cyclones._
  Wind moves in the opposite          │  Wind moves in same direction as
    direction to the hands of a watch.│    the hands of a watch.
  Barometer is lowest in the centre.  │  Barometer is highest in the
                                      │    centre.
  Area comparatively small.           │  Area comparatively large.
  Gradient from centre to             │  Gradient not steep.
    circumference steep.              │
  Short duration.                     │  Long duration.
  Velocity of wind great.             │  Air comparatively quiet.
  Weather bad; much rainfall.         │  Weather fine.
  Cool in summer; warm in winter.     │  Hot in summer; cold and frosty
                                      │    in winter.

Cyclones usually travel from west to east, and are always associated
with bad weather. The essential point in determining the character of
the weather, both in cyclones and anti-cyclones, is the barometric
gradient. Thus, according to the gradient, a cyclone may mean mild wet
weather, a gale, or a hurricane. The turning point of a cyclone, just
before the barometer begins to rise again, is called the _trough_.
Cyclones are usually oval in shape, except in the tropics, where they
are smaller and circular. The ordinary course of events in a cyclone is
shown in Fig. 44, reading it from left to right.

In =Secondary Cyclones=, bad weather is usually associated with a
stationary barometer and no wind. They are incompletely circular looped
concentric isobars, with the lowest pressure in the centre. They
frequently follow primary cyclones.

=V-shaped Depressions= are angular areas, with the lowest pressure in
the centre, frequently forming between adjoining anti-cyclones (Fig.
43). In the northern hemisphere the tip usually points south. They
usually move with great rapidity from east to west, and are always
associated with squalls or thunderstorms. Their movement is very
uncertain, and their forecast therefore more difficult than that of
cyclones and anti-cyclones.

[Illustration: FIG. 44.

WEATHER SEQUENCE IN A CYCLONE (_after Abercrombie_).

 The tracing indicates the line which a self-recording barometer would
 have marked. The arrows mark the shift of the wind, and the number of
 barbs denote the varying force of the wind.]

=Anti-cyclones= are associated with calm and cold in the centre, while
on the borders the wind blows around the centre, spirally outwards
in the direction of the hands of a clock. An anti-cyclone is usually
accompanied by a blue sky, dry cold air, a hot sun, a hazy horizon, and
little or no wind.

=Wedge-shaped Isobars=, unlike V’s, usually point north. They are
areas of high pressure moving along between two cyclones, being really
projecting parts of an anti-cyclone. The fine weather accompanying them
is only temporary, because they are never stationary, and are generally
followed by cyclonic disturbances. At the narrow end of the wedge
thunderstorms or showers often occur, and at the wide end fog is common.

=Cols= or necks of relatively low barometric pressure occur between
two anticyclonic areas. Like straight isobars they are intermediate
systems. Over cols the weather is dull and gloomy; in summer they may
be associated with thunderstorms.

=Straight Isobars= obviously do not enclose any area of high or low
pressure. They form an intermediate condition, preceding the formation
of a cyclone; and are usually associated with a blustering wind and
hard sky.

=Weather forecasting= is necessarily somewhat difficult and uncertain.
If one is dependent on _observations at a single point_ the following
rules are useful:—

 (_a_) If the barometer falls slowly and steadily bad weather will

 (_b_) The barometer falls for rain with S.W., S.E., and W. winds.

 (_c_) When the barometer falls rapidly, heavy storms may be expected.

 (_d_) The barometer rises rapidly for unsettled weather.

 (_e_) The barometer rises gradually for fine, settled weather.

The _Thermometer_ also is of great value as a weather indicator,
especially if one knows what is the average temperature at the place of
observation for each day of the year. Thus:—

 (_a_) A temperature continued for some time above or below the
 average, indicates a probable change.

 (_b_) Electric storms follow unusual warmth in summer.

 (_c_) A low thermometer and almost steady barometer are succeeded in
 winter by gales from N.N.W. or N.E.

The veering of the wind in England is also useful as an indicator.

 (_a_) When the wind, in shifting, goes round in the same direction as
 the hands of a clock—_i.e._, from N. by E. to S., or from S. by W. to
 N.,—favourable changes of weather may be looked for.

 (_b_) When the wind _backs_—that is, veers round in the opposite
 direction—bad weather generally follows.

The direction of the wind is an important factor. Thus:

 (_a_) Settled N.W. winds bring cold and fine weather.

 (_b_) Continued W. and S.W. winds are followed by rain.

Clouds give useful indications. Thus:—

 A _mackerel sky_, that is, one covered with lines of cirrus clouds,
 causing halos around the sun and moon, presages rain in summer and
 thaw in winter. By degrees the light clouds descend and pass into
 either masses of cumulus, or into dense, horizontal stratus, which
 form at sunset and disappear at sunrise. Both these kinds pass into
 the grey, shapeless nimbus, which soon covers the entire sky and is
 followed by rain.

When numerous observations can be _synoptically studied_, forecasting
becomes much more nearly certain. For this purpose telegraphic
communications are indispensable. The continent of Europe is better
placed than England for accurate forecasting. Areas of high pressure
coincide usually with large areas of land, of low pressure with large
surfaces of water. Thus England is placed near the boundary of the
usual anticyclonic and cyclonic systems, and its chief disturbances
come from the Atlantic from which early communication is impracticable.
Furthermore cyclonic disturbances may be diverted from their course
by a coastline or mountains or by the formation of an anticyclonic
area. In view of these uncertainties, the large proportion of correct
forecasts is somewhat surprising.

The =Moisture of the Air= depends upon the amount of vapour present in
it, and the ratio of this to the amount which would saturate the air at
the actual temperature. The former is called the _absolute humidity_,
the latter the _relative humidity_. The _dew point_ is the point at
which condensation of some of the vapour in the atmosphere occurs,
either as dew, rain, snow, or hoar-frost. The amount of moisture which
the atmosphere can retain before such condensation occurs, varies with
the temperature (see page 101). Thus the air is drier at noon than at
midnight, though the amount of vapour present in the two cases be the
same; and it is for the most part drier in summer than in winter. This
refers to the relative humidity, which is highest in cold weather. The
absolute humidity is higher in summer than in winter; it varies more
in continental than in maritime and insular climates; and there are
daily variations according to the state of the sky, the movements of
air, etc. The relative humidity is expressed as a percentage of what
would be required to produce saturation at the given temperature. The
usual relative humidity is 50 to 75 per cent. A moist air prevents
excessive changes of temperature due to radiation. It protects the
earth from too great intensity of the solar rays by day and from too
rapid loss of heat by radiation at night. The inhalation of a dry air
plays an important part in the cure of consumption. When the air is
almost saturated with moisture, evaporation from the skin and lungs is
diminished, and there is a feeling of oppression and disinclination to
work caused by the interference with the tissue changes of the system.

=Rainfall= is caused by over-saturation of a column of moist air. This
may be due to the contact of the air with a cold surface, as the ridge
of a mountain or a large surface of water, or to the impact of a colder

The amount of rainfall varies greatly. In some parts there is no rain,
as in the desert of Sahara; while on the south-east slopes of the
Himalayas, which are exposed to winds laden with moisture, it may be
several hundred inches.

The _latitude_ of a place has a great influence. As a rule the rainfall
decreases with increasing distance from the equator; but local
conditions may produce great modification, or even alterations of this

The _elevation above the sea-level_ has a varying influence. In the
Swiss Alps it is said that the rainfall increases with the elevation;
but this rule does not hold good in America.

The _nearness of large surfaces of water_ in summer tends to increase
the rainfall, when water is colder than its surroundings, while in
winter it has the opposite effect. The neighbourhood of the sea is for
the west of England and islands adjacent, a cause of increased rainfall.

The _influence of winds_ on the rainfall has been already considered.
In Great Britain south-west winds more especially increase the
rainfall. In their course they have travelled over the Gulf Stream
and the general equatorial current, and have thus received warmth
and moisture. The condensation of their moisture liberates a large
amount of latent heat, thus raising the temperature of this country.
In summer, however, south-west winds are _cool_ and moist, as the
Atlantic is not so hot as the continents of Asia and Europe over which
other winds have travelled.

In England the average rainfall is about 33 inches, in Scotland 46,
and in Ireland 38 inches. In the east of Great Britain, the rainfall
is from twenty to twenty-eight inches. On the west coasts of Scotland
and Ireland it is from 60 to 80 inches; and in some parts of Cumberland
may be about 150 inches per annum. The annual rainfall varies greatly
from the average for a number of years. In this country it has been
estimated that the maximum annual rainfall exceeds by one-third, and
the minimum annual rainfall is less by one-third than the average
rainfall of a series of years.

The _number of rainy days_ by no means corresponds with the amount
of rainfall. There are fewest rainy days at the equator, where the
rainfall is greatest. The rain diminishes the relative humidity of the
air, and purifies it from dust.



The Royal Meteorological Society recognises stations for the making and
recording of observations of three kinds: (1) _Second Order Stations_,
at which observations are taken twice daily at 9 a.m. and 9 p.m.; (2)
_Climatological Stations_, at which the observations are taken once
daily, at 9 a.m.; (3) Stations at which _one or more elements only_,
_e.g._ rainfall, _are observed_. All instruments used should have been
previously verified at Kew Observatory, so that the corrections for
index error may be known.

The =Barometer= used should be of a standard kind. Five chief kinds
of barometer are in use, only the last two of which are sufficiently
accurate for scientific purposes.

 1. _The Dial or wheel barometer_ consists of a bent tube A B, the open
 end of which supports an ivory float B. This, as it rises and falls
 with the mercury, by means of the rack C turns a wheel, in the axle
 of which a needle is fixed. The needle turns in one direction, or the
 other as the mercury rises or falls (Fig. 45); the dial is divided by
 comparing it with a standard barometer. As the ordinary variations of
 the barometer are from 28 to 31 inches, the circumference of the wheel
 is made exactly 1½ inches, and thus the float B will rise or fall
 1½ inches for a rise or fall of 3 inches in the barometer.

 [Illustration: FIG. 45.]

 2. The ordinary _syphon barometer_ (Fig. 46) consists of a bent tube
 attached to a piece of wood, and furnished with a screw _v_. The
 atmospheric pressure acts on the mercury at _d_, and the difference
 between the level of the mercury in the two arms of the syphon is the
 height of the barometer. To find the true height of the barometer the
 screw is turned till the shorter column stands at _a_ opposite zero.

 3. The _aneroid barometer_ is made by exhausting the air from a small
 round metal box. This box is closed by a flexible lid of metal which,
 being elastic, yields to changes in the atmospheric pressure. To the
 lower end of the lid a spring is attached which runs downwards to the
 floor of the box and resists the atmospheric pressure. The movements
 thus produced by variations in pressure are magnified by a rack
 and pinion, and so communicated to a long index which moves over a
 graduated scale.

[Illustration: FIG. 46.]

The standard Kew and Fortin barometers are both cistern barometers,
the mercury in the inverted tube communicating with the mercury in a
cistern below.

 4. The _Kew pattern barometer_ has a closed cistern below, the area
 of which being accurately known, the inches on the scale are not
 real inches, but inches of pressure, _i.e._ inches so shortened
 as to compensate for the rise of the mercury in the cistern. This
 compensation is necessary inasmuch as changes in atmospheric pressure
 affect the level of the mercury in the cistern as well as of that in
 the tube.

 5. In the _Fortin barometer_ (Fig. 47) the cistern has a pliable
 base of leather, which can be raised or lowered by means of a screw.
 The upper part of the cistern is made of glass, a piece of ivory
 indicating the zero of the scale. Before taking a reading, the level
 of the mercury must always be set exactly to this point by means of
 the screw. The Fortin is the most sensitive form of barometer, and the
 adjustment required in order to take a reading is easily performed.

To ensure more accurate reading of the barometer, a secondary scale or
=vernier= is used, which slides upon the principal scale. This vernier
is so graduated that 25 of its divisions correspond to 24 of the
divisions on the fixed scale. The fixed scale is divided into inches,
tenths (·1), and half-tenths (·05). Each division of the movable scale
or vernier is therefore shorter than each division of the scale by 1∕25
of ·05, _i.e._ ·002 inch. Consequently the vernier shows differences of
two thousands of an inch.

[Illustration: FIG. 47.


 _a_—Attached thermometer. _b_—Screw of vernier. _c_—Screw for setting
 level of cistern.]

 _Method of reading Fortin’s Barometer._—First note the reading of
 the attached thermometer; next turn the screw at the bottom of the
 cistern, so that the ivory point just touches the surface of the
 mercury. Next adjust the vernier by means of the rack and pinion at
 the side of the barometer (Fig. 47) so as to bring its two lower
 edges exactly on a level with the convex surface of the mercury. In
 reading the barometer, first read off the division next below the
 lower edge of the vernier. In Fig. 48 this is 29·05. Then the true
 reading is 29·05 _plus_ the vernier indication. Next look along the
 vernier until one of its lines is found to agree with a line on the
 scale. In Fig. 48 this is at the fourth division on the vernier. But
 each of the figures marked on the vernier counts as 1∕100 (·01), and
 each intermediate division as 2∕1000 (·002); hence the reading of the
 vernier will be ·008 inch, and the reading of the barometer 29·05 +
 ·008 = 29·058 inch. If two lines on the vernier are in equally near
 agreement with two on the scale, the intermediate value should be

Certain _corrections_ are required in the actual reading for (1) index
error; (2) temperature; and (3) height above sea-level.

The _index error_ is found by comparison with a recognised standard
at Kew. Correction for _temperature_ is required. Every barometer has
a thermometer attached, and the reading is reduced to the standard
temperature of 32° F, by means of tables such as are given on page 32
of Marriott’s _Hints to Meteorological Observers_.

The height of the _cistern_ of the barometer above _sea-level_ should
always be exactly obtained.

The correction necessary to reduce observations to sea-level (_i.e._
mean half-tide level at Liverpool), depends on the temperature and
pressure of the air, as well as on the altitude. The data for this
correction are given in Table III. of Marriott’s _Hints_.

[Illustration: FIG. 48.


=Thermometers.=—The =maximum thermometer= may be on Negretti and
Zambra’s, or on Phillips’ principle. In the former (Fig. 49) the bore
of the tube is reduced in section near the bulb (A) in such a way that
while the expanding mercury forces its way into the tube, the column
of mercury breaks off on contraction, so that its upper limit shows
the highest temperature that has been reached. The thermometer is set
by holding it bulb downwards and shaking to make the mercurial column
continuous. It is mounted in the screen horizontally (Fig. 51).

[Illustration: FIG. 49.


The =minimum thermometer= chiefly used is Rutherford’s. It contains
spirit in which is an immersed index (A, Fig. 50). With a falling
temperature the spirit draws the index along with it; but on rising
again, the spirit passes the index, leaving it at the lowest point to
which it has been drawn. Thus the end farthest from the bulb registers
the minimum temperature. The instrument is set by raising the bulb and
allowing the index to slide to the end of the column of spirit. The
thermometer must be firmly fixed and mounted quite horizontally.

[Illustration: FIG. 50.


=Thermometer Screen.=—The above thermometers, as well as the dry and
wet bulb thermometers are mounted in a Stevenson’s screen (Fig. 51).
This is a doubled-louvred box through which the air can pass freely,
but the sun cannot enter. The horizontal position of the maximum and
minimum and the vertical position of the dry and wet bulb thermometers
are shown in Fig. 51.

Three additional thermometers are usually included in a well-organised
meteorological station.

A =minimum thermometer= placed on the grass gives the lowest
temperature on the grass, which is often considerably lower than that
of the neighbouring gravel walk. This record is chiefly useful for
agricultural purposes.

The =earth thermometer= chiefly used is shown in Fig. 52. It consists
of a sluggish thermometer mounted in a short weighted stick attached
to a strong chain, and of a stout iron pipe which is drawn out at the
bottom to a point and driven into the earth, usually to a depth of 4

=Solar radiation= is measured by black-bulb and light-bulb thermometers
in _vacuo_, which are mounted on a post 4 feet above the ground and
record the maximum temperature.

=Humidity= in the air is measured by direct or indirect hygrometers.
Of the former Dines’, Daniell’s, and Regnault’s are the best known,
but as they are not used in observations acknowledged by the Royal
Meteorological Society, the reader may be referred to their description
in books on physics. The indirect hygrometer which is universally
employed in this country is that furnished by the =dry and wet bulb
thermometers=. In frosty weather they require much attention, and then
a Saussure’s hair hygrometer may be used as supplementary. The general
arrangement of the dry and wet bulb thermometers is shown in Fig. 53.

[Illustration: FIG. 51.


The wet bulb is covered with a single layer of soft muslin, while a
noose of six to eight strands of darning cotton connects the neck of
the wet bulb with a covered water receptacle 2 to 3 inches distant,
below and at its side. This receptacle is kept filled with rain-water.

[Illustration: FIG. 52.


[Illustration: FIG. 53.


From the readings of the dry and wet bulb thermometers three deductions
can be made:

1. The temperature of the dew point.

2. The elastic force of aqueous vapour.

3. The relative humidity.

The =dew point temperature= is that temperature at which the outside
air at the time the observation is taken will deposit the moisture
contained in it. It is the temperature at which the air is saturated
with moisture. It is calculated from the readings of the wet and dry
bulb thermometers

 (_a_) by Glaisher’s tables; (_b_) by Apjohn’s formula.

Glaisher’s tables are based on a series of numbers called Greenwich
or Glaisher’s factors, which he determined by comparison between
observations made with the dry and wet bulb thermometers and with
Daniell’s hygrometer. The formula for using the factors is as follows:—

  d = D - {(D - W) × f}

where d = dew point, D = dry bulb temperatures, W = wet bulb
temperature, and f = factor.

The following examples are from Glaisher’s table of factors.

  │THERMOMETER FAHR.  │       │
  │        55°        │ 1·96  │
  │        56°        │ 1·94  │
  │        57°        │ 1·92  │
  │        58°        │ 1·90  │
  │        59°        │ 1·89  │
  │        60°        │ 1·88  │

             Thus, if D = 60°,
                      W = 55°,
  then dew point = 60 - {(60 - 55) 1·96}
                 = 50°·2.

The dew-point may also be obtained by Apjohn’s formula; which for a
pressure of about 30 inches is F = f-(D-W)/87

 D being dry and W wet bulb temperature,

 F elastic force of vapour corresponding to dew-point, and

 f, elastic force corresponding to wet bulb temperature (ascertained
 from a table of tensions).

The _elastic force of aqueous vapour_, _i.e._ the amount of barometric
pressure due to the vapour present in the air is dependent upon the
temperature of the dew-point. It is given for every tenth of a degree
of temperature in Table VI. (p. 42) of Marriott’s _Hints_.

The _relative humidity_ is a term expressing the percentage of
saturation of the air with water vapour. It is obtained from Table VI.
(above) as follows:—

               Elastic force of water vapour at the temperature of the
  Relative }                  dew-point
           } = ——————————————————————————————————————————————————————————
  Humidity }   Elastic force of water vapour at the temperature of the air
                  (_i.e._ the dry-bulb reading.)

  Thus elastic force with dry bulb  = 55° is ·433 in.}  in the table.
          „          „    dew-point = 46°·5 is ·317 in.}

  ·317/·433 = ·73.

  If saturation = 100, relative humidity is 73.

In Table VII. of Marriott’s _Hints_, a table is given which enables
the relative humidity to be found by mere inspection. Thus if the dry
bulb temperature is 58°·5, wet-bulb 51°·7, and the difference 6°·8, the
relative humidity given in the table is 62.

The =Rain-Gauge= is best made of copper in the shape of a circular
funnel, usually 5 or 8 inches in diameter, leading into a bottle
underneath. It must always be set in an open situation away from trees,
walls, and buildings. According to Scott no object ought to subtend
a greater angle with the horizon than 20° in any direction from the
gauge. The rain is measured by pouring the contents of the bottle into
a glass measure, which is graduated to represent tenths and hundredths
of an inch on the area of the gauge, the measure holding half an inch
of rain on this area. Snow is melted before being measured.

[Illustration: FIG. 54.


A. Copper Upper Part of Gauge. B. Funnel. C. Bottle. To the right is
shown the glass measure inverted.]

Observations of =wind= should include its direction and force. The
direction is observed by means of a well-oiled and freely exposed vane.
There are 32 points to the compass, but a reading to eight points
suffices. The force of the wind should be estimated by Beaufort’s
scale, from 0 to 12. Thus:—

  0.  _Calm_            3
  1.  _Light air_       8
  2.  _Light  breeze_  13
  3.  _Gentle_         18
  4.  _Moderate_       23
  5.  _Fresh_          28
  6.  _Strong_         34
  7.  _Moderate gale_  40
  8.  _Fresh_          48
  9.  _Strong_         56
  10. _Whole_          65
  11. _Storm_          57
  12. _Hurricane_      90

_Robinson’s anemometer_ is also employed, but it is not altogether

=Sunshine= is recorded by the Campbell-Stokes burning recorder, and the
Jordan photographic recorder. Of these the former is the more easily
worked and gives more uniform results. It consists of a sphere of glass
4 inches in diameter, supported on a pedestal in a metal zodiacal frame
(Fig. 55). The setting of the recorder should be due south, level from
east to west, and with the axis of the ring inclined to the horizon
at an angle equal to the latitude of the place, and so that the image
of the sun, when the sun is due south, shall fall on the meridian
line marked on the ring. The sun burns away or chars the surface of
the cards inserted in the proper groove, and so gives a record of the
duration of bright sunshine.

[Illustration: FIG. 55.


The amount of =Cloud= should be estimated daily, according to a scale
ranging from 0 to 10, _i.e._ clear sky up to completely overcast.
The form of cloud should also be stated, as cirrus, cirro-cumulus,
cirro-stratus, cumulus, cumulo-stratus, stratus, and nimbus.



Certain personal factors are very important in relation to health. The
chief of these are constitution, temperament, heredity, idiosyncrasy,
age, sex, and habits.

=Constitution.=—Health may vary in degree without the presence of
actual disease. This fact is expressed by the use of such terms as
“perfect,” “strong,” “feeble,” “delicate,” in speaking of the health
of the same person at different times, and also as distinguishing
one person from another. The constitution is an important factor in
resisting disease, and a robust constitution may determine recovery
from a severe illness, while the patient with a feeble constitution
falls a victim to it.

The constitution of an individual is partly _acquired_, partly
_inherited_. A feeble or delicate constitution may be acquired by
unhygienic conditions, such as deficient exercise, the prolonged
breathing of impure air, unhealthy occupations, some imperfection in
diet, or dissipation.

But while many a robust constitution is enfeebled by such conditions,
a weak constitution may happily be strengthened by careful and
prolonged attention to the laws of health. This is especially well
seen in the case of those who strengthen their muscular system by
carefully-graduated and not excessive exercise.

=Heredity= has a great influence on health. As a rule the children of
healthy parents are robust, and on the contrary, any “weak point” in
the parents’ constitutions is liable to be participated in by their
children. Both _mental_ and _physical_ conditions may be inherited. A
peculiar habit of mind, as well as the same expression of features, may
be inherited.

As regards physical diseases, the influence of parents is not less
remarkable. The son of a gouty father requires to be particularly
abstemious in order to avoid his father’s disease. Certain specific
febrile diseases, _e.g._, enteric fever, diphtheria, and still
more rheumatic fever, are hereditary in the sense that the members
of certain families are more prone to them than others. Insanity,
epilepsy, asthma, neuralgia, and hysteria are also hereditary in the
same sense, and it is noticed that they occasionally alternate in
different generations. Cancer, consumption, certain skin diseases, and
a tendency to the early onset of degenerative diseases, appear also to
occur more often in certain families than in others.

In most cases it is the tendency to disease which is transmitted,
and not the disease itself. When an actual disease is inherited, as
happens very rarely in tuberculosis and often in syphilis, the actual
infection is transmitted before birth from the parent.

A peculiarity of form, character, or tendency to disease has been known
to disappear in one generation and re-appear in the next; this variety
of heredity is termed _atavism_. The evidence showing the inheritance
of acquired characters, _i.e._ those which arise in consequence of the
effect of external forces on the organism is not conclusive. Weismann
believes that only those forces that influence the germ-plasm are
inherited. It must be admitted that the instances of inheritance of
acquired characters can be better explained otherwise. Thus the long
neck of the giraffe was formerly explained on the supposition that the
neck became gradually lengthened owing to the efforts made generation
after generation in reaching food; but is better explained by Weismann
on the supposition that those giraffes which, during times of famine
were able to reach higher and obtain food from the twigs of trees would
survive and pass on their characteristics to their young, while shorter
necked giraffes would be exterminated.

The inheritance of proclivity to or immunity from attacks of infectious
diseases is a problem of great difficulty; but there is no substantial
reason for thinking that the efforts being made to diminish the
prevalence of these diseases (including consumption) are likely to
produce a weaker race or one more likely to suffer with excessive
severity from these diseases should they be introduced after a long
absence. (See also page 309).

=Temperament= indicates a peculiarity in constitution, causing a
liability to particular diseases, or to a special character in any
disease to which a person becomes subject. Four temperaments are
usually recognized—the sanguine, phlegmatic, bilious, and nervous, but
unmixed specimens of these temperaments are rarely seen.

By =idiosyncrasy= is understood a peculiarity limited to a
comparatively small number of individuals. Four varieties of
idiosyncrasy may be described.

The first consists in an extreme susceptibility to the action of
certain things, or an extreme lack of susceptibility. Thus most people
at some time or other inhale the pollen of grasses, but only in a few
cases does it produce that troublesome and distressing complaint—hay
asthma. In certain persons a very minute dose of iodide of potassium
produces distressing symptoms; in most cases these symptoms arise if
the drug is taken for a prolonged period; but in a few cases it may be
taken for an indefinite period without troublesome result. The case of
a physician at Bath is very curious. The smell of hyacinths in bloom
always made him faint away; so constant was this result, that before
entering a room during the hyacinth season, he always asked the servant
if there were any hyacinths in it.

The second form of idiosyncrasy consists in the production of poisonous
results by common articles of diet. Thus some people cannot partake
of shell-fish or lobsters without having severe nettlerash. In rare
instances the smallest amount of egg, or in other cases mutton, or
pepper, or some other substance will produce severe indigestion or

The third form consists in an inversion of the usual effects of certain
substances, especially drugs. Thus opium in rare cases produces
convulsions; while the aperient Epsom salts have been known to produce

A fourth form, that of mental idiosyncrasies, may be added, as where
there is a strange preference or aversion for objects usually regarded
as indifferent. Many cases of mental peculiarity, short of actual
insanity, will come under this head; as will instances of depraved
appetite for food, etc.

=Age and Sex.=—According to the period of life, danger arises from
different sources. In _infancy_ and old age extreme changes of
temperature are especially dangerous, and additional protection is
required (see also page 271). Thousands of deaths occur in the first
year of life, from substituting starchy foods for milk, the natural
food for infancy and childhood (see page 303). In _childhood_ the
danger from bad feeding is still present, and is evidenced by the
frequency of rickets (page 28); infectious diseases claim their
thousands; and the disorders associated with dentition are common. In
_youth_ rapid growth is proceeding, and so the food must be abundant
and nutritious. A proportionately larger amount is required than by an
adult, as the functions of the body not only require to be carried on,
but material is necessary to build up the growing tissues.

_Manhood_ is the period of greatest stability of health. The health now
depends on the use made of the previous periods of life, and on the
habits acquired.

With the onset of _old age_ come various degenerative diseases. The
tendency is to death by gradual decay—a _euthanasia_ or easy death,
which is too seldom seen. Commonly, bronchitis or apoplexy or kidney
diseases bring the scene to a somewhat premature end.

The mortality of man is greater than that of woman at all ages except

=Habits.=—The immense power of habits in the formation of character is
perhaps duly appreciated; but their influence on physical health is not
so well appreciated; though it would be difficult to exaggerate it.
The laws of health are as inexorable and unaltering as all other laws
of nature; and whether broken through carelessness or ignorance, the
Nemesis of disease inevitably follows. Whatever a man sows he reaps, in
health as in other matters.

Habits are easily formed; but, when once formed, not so easily broken.
They ought to be our servants; very commonly they become our masters.

In reference to _eating and drinking_, habits regular as to time and
moderate as to quantity are especially important. The habit of eating
hastily and masticating the food imperfectly, is certain, sooner or
later, to produce disease. Over-eating, again, is a fertile source of
disease, especially when the excess is in animal food. The amount of
stimulation produced by a given dose of alcohol, gradually diminishes
with its repetition; the consequence is, that in order to produce
the amount of stimulation to which the system has become habituated,
the stimulant requires to be gradually increased. The craving for
stimulants is often a sign of ill-health, owing to disregard of
hygienic laws or actual disease. Not infrequently it is due to
badly-ventilated rooms or long hours of work without food, producing
a sense of depression which food does not immediately allay. When the
cause is unknown, recourse should be had to competent medical advice,
and not to the brandy bottle.

=Attention to the Action of the Bowels= is a matter which is commonly
neglected. The importance of a regular habit in this respect cannot be
exaggerated; the bowels should always be relieved at a particular time
each day. Where this does not occur the condition of _constipation_
results. Owing to the retention of the fæces in the intestines beyond
the normal period, the stomach and higher parts of the intestines do
not perform their functions normally; indigestion and “dyspepsia,”
accompanied by headache, flatulence, and other symptoms follow.
Hæmorrhoids (piles) are another frequent consequence. At the junction
of the small and large intestines is a dilated sac (in the cæcum).
This becomes distended when constipation occurs; inflammation may
be set up, and an operation required, or the condition is fatal.
Powerful purgative medicines are injurious to the bowels, and they tend
afterwards to increase constipation. It is better to take slow-acting
aperient remedies, and better still not to take any at all, but relieve
the condition by means of such articles of diet as stewed fruit, pears,
figs, olive oil, or brown bread. As a rule more exercise is required in
this condition, and always a prompt attention to the calls of nature.



=Physiological Considerations.=—In the strict sense of the word,
exercise signifies the performance of its functions by any part of
the body; thus, digestion is exercise of the stomach, respiration is
exercise of the lungs, thinking is an exercise of the brain. But the
term is usually applied chiefly to muscular contraction, and restricted
to contraction of voluntary muscles. Involuntary muscles, which are
concerned in the carrying on of the unconscious organic functions of
life, are not directly controllable, and so their growth and state
of nutrition cannot be regulated. There are two sets of involuntary
muscle, which are of special importance—the heart and the muscles of
respiration. The heart contracts at least sixty times per minute; the
respiratory muscles contract about seventeen times per minute; and this
amount of exercise goes on throughout the whole day. But although we
cannot make our hearts beat quicker by a direct volition, and cannot
breathe more rapidly than usual beyond a few seconds, yet a brisk walk
will cause increased action of the heart and respiratory muscles,
as well as a vigorous contraction of the muscles directly concerned
in walking. Going uphill is a valuable exercise for the heart. The
vermicular contractions of the intestines are to some extent also
increased by voluntary exercise, through the indirect excitation of the
whole system; thus, exercise is an important element in the treatment
of constipation.

The muscles contain about a fourth of the whole blood of the body, and
a very large share of the metabolism (page 4) of the body occurs in

Hence the importance of keeping them in a healthy condition by
exercise. The great danger is of not equilibrating the muscular and
nervous functions. The ideal condition is where neither mental nor
muscular culture is neglected, but both are co-ordinated to the
production of a healthy man.

=Effects of Healthy Exercise.=—1. _The Nutrition of the Muscles_ is
improved. The volume, density, and energy of the muscles are increased.

2. _The action of the lungs is increased._ Dr. E. Smith found that if
the air inspired while lying down be represented by unity, the amount
inspired when erect is 1·33; when walking at the rate of one mile
per hour, 1·9; at four miles per hour, 5; at six miles per hour, 7;
riding on horseback, 4·05; swimming, 4·33. Or, putting it in another
way, under ordinary circumstances a man inspires 480 cubic inches
per minute; if he walks four miles per hour, he inspires 2,400 cubic
inches; if six miles an hour, 3,260 cubic inches.

At the same time the amount of carbonic acid expired is increased.
Its amount bears a nearly constant relation to the amount of muscular
exercise, and consequently the amount of carbonic acid eliminated in
various forms of exercise affords a just estimate of their relative
value. The increased elimination of carbonic acid, the corresponding
increased absorption of oxygen, and the absence of increase of
elimination of urea are shown in the following summary of observations
by Pettenkofer and Voit:—

  │          │    OXYGEN   ├──────────────┬──────┬─────┤
  │_Work day_│     955     │    1284      │ 2042 │ 37·0│
  │_Rest day_│     709     │     912      │ 828  │ 37·2│

The above amounts are for the entire day. During actual exercise the
excess of elimination of carbonic acid is much greater. Thus, Dr.
E. Smith experimentally found that if the amount of carbonic acid
eliminated during rest be represented by one, the amount walking at two
miles an hour and carrying 7 lbs = 1·85, the amount walking at three
miles an hour = 2·64.

Alcohol diminishes the excretion of carbonic acid, and should therefore
be avoided during muscular training.

By muscular exercise the size of the lungs is increased, and their
_vital capacity_, that is, the amount of air capable of being expired
after a forced inspiration, is considerably increased. Corresponding
with this increase of vital capacity, exercise, especially that in
which the arm and chest muscles are systematically developed, increases
the size of the chest. A perceptible difference in the circumference of
the chest may be noticed after only a few weeks’ methodical exercise.

3. _The action of the skin is increased._—Sensible perspiration is
commonly induced, but less readily in those habituated to hard work.
Insensible perspiration is always increased.

4. _The temperature of the body_ is not increased, so long as
perspiration occurs. Every muscular contraction involves the production
of heat; but this is counteracted by increased evaporation from the
skin, and by the circulatory current carrying the hotter blood to every
part of the body, and so rapidly equalising its temperature. Chilblains
are due to the defective circulation of the blood, and can in most
cases be cured by active exercise aided by warmer clothing and an
abundant supply of oxidisable food.

5. _The Heart and Blood-vessels._—By exercise the heart’s action is
increased in frequency and force. The pulse usually increases from
ten to thirty beats per minute above the rate while at rest. After
prolonged exercise it may temporarily fall below the normal standard.

6. The _Digestion_ and assimilation of food are aided by exercise,
especially when taken in the open air.

7. _The nervous system_ is improved in nutrition and power by a
moderate amount of exercise. In fact, a certain amount of muscular
exercise is essential for a healthy mind.

8. _The elimination of urea_ is not increased by exercise. Evidently
then it is not the metabolism of the nitrogenous substance of the
muscles which supplies the energy for muscular contraction; but of the
other oxidisable and non-nitrogenous substances (such as glycogen and
sugar) contained in them.

In practice it is found that with exercise more nitrogenous and
non-nitrogenous food are both required.

=Effects of Excessive Exercise.=—After prolonged exertion muscles
become _exhausted_. This is associated with an accumulation in the
muscles of the products of their action (especially sarcolactic acid).
Then rest becomes necessary, in order that the effete products may be
removed, and the nutrition of the muscles restored.

Long-continued over-exertion produces _chronic exhaustion_, which
may, if excessive, cause wasting of muscles. Exhaustion is much more
liable to occur when a small group of muscles are exercised out of
all proportion to others. Thus, in clerks, we have what is known as
the _writer’s_ or _scrivener’s palsy_. The muscles of the hand, and
especially of the thumb, cease to respond to the volition of the
writer, but are seized with spasm every time writing is attempted; and
the muscles of the thumb tend to waste. A similar condition sometimes
arises in violinists, tailors, etc. The practical inference from
these facts is, that one group of muscles should not be exercised
disproportionately to the muscles of the rest of the body, and that
proper intervals of rest should be allowed.

Excessive exercise of the whole muscular system is very apt to harm
those of previously sedentary habits. A walking tour entered on with
more zeal than discretion, and not taken by easy stages for the first
few days, is often productive of more harm than good.

In the intervals of great mental labour, as with students, the amount
of exercise should not be _suddenly_ increased, but should be regular
and moderate in amount.

Competitive exercise should be strictly regulated. The Oxford and
Cambridge crews have been said to acquire heart-disease more commonly
than the average, but this is not correct. Hypertrophy of the heart may
occur as the result of severe exercise, and this within certain limits
is not an abnormal condition. Occasionally dilatation of the heart has
been produced in weakly lads.

=Amount of Exercise Desirable.=—According to Parkes, the average daily
work of a man engaged in manual labour in the open air is equivalent
to the work involved in lifting 250 to 350 tons one foot high; this is
a moderate amount, 400 tons being a heavy day’s work. The amount of
muscular exercise involved in this may be easily known by remembering
that a walk of 20 miles on a level road is equivalent to about 353-2∕3
tons lifted 1 foot; and that a walk of 10 miles while carrying 60 lbs.
is equivalent to 247½ tons lifted 1 foot. (Haughton).

 The _amount of work done_ by a healthy adult per diem is stated by
 M. Foster to be about 150,000 metre-kilogrammes (_i.e._, 150,000
 kilogrammes lifted 1 metre). Metre-kilogrammes can be converted into
 foot-pounds by multiplying by 7·233; into foot-tons by multiplying by
 ·003229; 150,000 metre-kilogrammes therefore equal 484·35 foot-tons.
 This is considerably in excess of Parkes’ estimate, but in certain
 laborious occupations this high amount is reached.

 In addition to this amount of external work, there is the internal
 work of the heart, muscles of respiration, digestion, etc. This is
 estimated by Parkes at about 260 foot-tons.

 The internal and external muscular work of the body together amount to
 about 1∕7th to 1∕8th of the total force obtainable from the food.

Every healthy man probably ought to take an amount of exercise
represented by 150 tons raised 1 foot, which is equal to the work
done in walking 8½ to 9 miles on a level road. A certain amount
of this exercise is taken in performing one’s daily work; but apart
from this, out-door exercise should be taken equivalent in amount to a
walk of five or six miles. It is impossible to lay down rules to suit
all cases, but a less amount of exercise than that named is probably
incompatible with perfect health.

=Effects of Deficient Exercise.=—The _muscles_ themselves become
enfeebled and wasted. Some wasting of muscle occurs after a few days’
confinement to bed; and a limb confined in a splint speedily loses
its healthy, rounded contour. _Oxidation processes_ are diminished;
less carbonic acid is eliminated, and it tends to accumulate in the
system, owing to the diminished activity of respiration. In consequence
of the diminished oxidation, the temperature of the body is not well
maintained, and the heat is not uniformly distributed. Cold feet are
a common complaint of those who lead sedentary lives, though seldom
complained of by others.

Along with the other muscles, the _heart_ becomes enfeebled and the
circulation less perfect. _Digestion_ is enfeebled; the appetite is
poor. The _nervous system_ also suffers; nervous irritability is a
common result, while sleeplessness—a thing almost unknown among those
who live by the sweat of their brow—is becoming much more common among
the worried and ill-exercised inhabitants of our towns.

Many diseases are favoured by deficient exercise, and can be averted by
systematic exercises and the concomitant increased supply of pure air.
It is often difficult to appraise the relative merits of exercise and
pure air; but there can be no doubt that both are of extreme importance.

The prevention of consumption, even in those with a strong hereditary
tendency, is greatly helped by systematic exercises, especially those
directed to the expansion of the chest cavity. In cases of consumption
there is commonly a history of deficient exercise or an occupation
involving a cramped position, as well as of living in an impure air.

Various deformities are induced by defective exercise of particular
groups of muscles. Thus drooping shoulders may be caused by
shoulder-straps confining the action of the shoulder-muscles in the
earlier years of life. Stooping is favoured by sitting in cramped
positions in school, and by the use of desks not inclined at the proper
angle. Lateral curvature of the spine is due to weakness of the muscles
of the back, and is best treated in its earlier stages by gymnastic
exercises specially directed to strengthening these muscles. The
tendency to such curvatures is greatly increased in girls by the fact
that their trunks are imprisoned in corsets as if in splints, and so
exercise of the trunk muscles is reduced to a minimum.

=Rules respecting Exercise.= 1. _The clothing during exercise should
not be excessive_, and should not interfere with the free play of
the limbs, nor with full expansion of the chest. Flannel is the best
material to wear next the skin, as it absorbs perspiration without
becoming non-porous.

2. _Avoid chill after exercise._ It is well, if there has been any
perspiration during exercise, to strip and scrub the skin, particularly
about the chest and arm-pits, with a rough towel.

3. _Exercise should be systematic and regular._ It is important to
avoid sudden, violent, and competitive exercise. No severe exercise
ought to be undertaken without a gradual training.

4. _The amount of exercise must be regulated by individual fitness._
A chain is no stronger than its weakest link. The muscles may be
stronger than the heart or lungs, and the latter may be fatally injured
by an amount of exercise which the muscles can well bear. Hence the
importance of ascertaining the condition of the vital organs before
entering on a course of training.

Another important bearing of this rule is in relation to the exercise
of growing boys and girls. When we remember that a boy at school will
sometimes grow six to eight inches in a year, it is evident that much
energy is being expended in this direction, and that _excessive_
gymnastic exercise can only do harm. Between the ages of fifteen and
seventeen there is usually the greatest amount of physical development,
and if there is great muscular strain at this period, growth is
interfered with, and the power of resistance to disease may be
seriously lowered.

5. _Every part of the body ought to be exercised._ This is done
spontaneously by the infant. Every muscle of his body acts in sheer
delight. The evils of exercise confined to particular groups of muscles
have been already described. Lawn tennis is very valuable as affording
exercise for both limb and trunk muscles.

6. _Exercise should not be taken immediately after meals_, as thus
digestion is interfered with.

7. _Exercise should be taken, as far as possible, in the open air._ A
small amount of exercise out of doors is much more invigorating than a
large amount indoors.

=The Forms of Exercise= taken may be divided into recreative and
_educational_, though both of course may be recreative under many

The primarily recreative exercises, such as rowing, cricket, football,
tennis, hockey, will, it may be hoped, be never replaced by educational
gymnastics, though the latter possess a high value. The recreative
influence as well as the influence on the power of self-control of such
games as cricket and football render them of national importance.

Educational gymnastics can be applied to exercise the muscles of
any part of the body, and can be exactly graduated to individual
requirements. Singing, speaking, and reading aloud, are forms of
muscular exercise very much neglected, and they are particularly
important, as the lungs and voice are by these means greatly
strengthened, and rendered much less liable to the inroads of disease.

 Professor Haughton has shown that the work done by a man walking on
 a level surface at the rate of three miles an hour is equivalent to
 raising his own weight, _plus_ the weight he carries through 1∕20 of
 the distance walked.

  Thus, if W = weight of the man,
         W^1 = weight carried by him,
           D = distance walked in feet,
           C = co-efficient of traction (1∕20, at three miles an hour),

 then we obtain by the following formula the amount of work done, the
 co-efficient of traction being multiplied by 2,240 (the number of
 pounds in a ton) to obtain the result in foot-tons.

  (W + W^1) × D/(C × 2,240)

 In ascending a height, a man raises his whole weight through the
 height ascended.

 _A regiment of soldiers marches ten miles, each carrying a weight of
 60 lbs. What amount of work is performed by each soldier?_

If we assume the average weight of each soldier to be 150 lbs., and
that the march was at the rate of three miles an hour, then—

(150 + 60) × 10 × 5,280/(20 × 2,240) = 247·5 foot-tons.

In this example it is assumed that the march is on entirely level
ground that all weights are carried in the most convenient manner, and
that the rate of travel is three miles an hour. Velocity is gained at
the expense of carrying power. It has been found that the amount of
work is generally inversely as the square of the velocity. Haughton has
determined from Weber’s calculations the co-efficient of resistance for
three velocities.

  │                     │     OR RESISTANCE.     │
  │ 1·818 miles per hour│        1∕28·27         │
  │                     │                        │
  │ 4·353   „        „  │        1∕13·70         │
  │                     │                        │
  │10·577   „        „  │         1∕7·51         │

Parkes has extended these calculations to show the distance in miles
required to be travelled at various velocities to do work equal to 300
foot-tons, and the time required in each instance.

  │               │               │DISTANCE FOR MEN OF│ TIME REQUIRED  │
  │               │               │                   │  hrs.   mins.  │
  │       2       │    1∕26·74    │       12·2        │   10     36    │
  │               │               │                   │                │
  │       3       │    1∕20·59    │       16·3        │    5     24    │
  │               │               │                   │                │
  │       4       │    1∕16·74    │       13·3        │    3     18    │
  │               │               │                   │                │
  │       6       │    1∕12·18    │        9·6        │    1     36    │
  │               │               │                   │                │
  │       8       │     1∕9·60    │        7·6        │    0     57    │
  │               │               │                   │                │
  │      10       │     1∕7·89    │        6·3        │    0     38    │

The co-efficient 1∕20, corresponds very nearly to 3·1 miles per hour,
and it appears that at this rate of travel the greatest amount of work
can be done with the least expenditure of energy.

_How much work is done by a man weighing 150 lbs. who walks 15 miles up
an incline 1 in 200?_

The number of feet ascended in 15 miles

  = 5,280 × 15∕200 = 396.

The amount of work done by the man in raising his own weight 396 feet

  = 396 × 150∕2,240 = 26·5 foot-tons.

The amount of work done in walking 15 horizontal miles at the rate of 3
miles an hour

  = 150 × 15 × 5,280/(20 × 2,240) = 265.2 foot-tons.

  Total amount of work done = 265.2 + 26.5

                            = 291.7 foot-tons.

_Eight palanquin bearers carry an officer weighing 180 lbs. and a
palanquin weighing 250 lbs., a distance of 25 miles. Assuming that
each man weighs 150 lbs., what amount of work was done by each man?

  250 + 180 = 430

  150 × 8 = 1,200
  W + W^1 = 1,630

  1,630 × 25 × 5,280/(20 × 2,240) = 4,802·7 foot-tons.

This being the total work done, the work per man = nearly 600.3

_A hill-coolie weighing 150 lbs. goes 30 miles with an ascent of 5,500
feet in three days, carrying 80 lbs. in weight. What is the work per
day? (Parkes.)_

Work of the ascent = (150 + 80) × 5,500∕2,240 = 564·7 foot-tons.

Work of 30 miles walk = 230 × 30 × 5,280/(20 × 2,240) = 813·2 foot-tons.

Total work = 564·7 + 813·2 = 1,377·9.

Total work per day = 1,377·9∕3 = 459·3 foot-tons.

_Suppose a man weighing 150 lbs. in his clothes, carries a load of
bricks weighing 35 lbs. up a perpendicular ladder 30 feet high, 100
times daily, what amount of work does he do; and what will it equal in
miles walked upon a flat road at the rate of 3 miles an hour?_

  ((150 + 35) × 30 × 100) / 2,240 =  247·8 foot-tons

         (185 × D) / (20 × 2,240) = 247·8.

                      Therefore D = 60,056 feet

                                  = about 11·4 miles.

_Suppose a man strikes 12,000 strokes in 5 hours with a 14-lb. hammer,
raising it at each stroke 4 feet, how much work does he do? Compare
this with a walk of 15 miles on a level ground at 3 miles an hour, the
weight of the man and what he carries being 180 lbs._

  (_a_) 12,000 × 14 × 4 = 672,000 foot-lbs. of work

                        = 300 foot-tons.

  (_b_) (180 × 15 × 5,280) / (20 × 2,240) = 318·2 foot-tons.

The two amounts of work are related as 300: 318·2.



=Physiological Considerations.=—Life is made up of alternations of rest
and action. The exercise of any organ is followed by a necessary period
of repose, during which the oxidised materials produced by functional
activity are removed by the blood, and carried to the excretory organs;
while at the same time fresh nutritive material is supplied by the
blood to make good the losses thus sustained.

The only apparent exceptions to this rule of alternation of rest and
exercise are the heart and lungs, and some less important organs acting
out of the control of personal volition. But even these organs obey
the universal law. The difference is that their rest is very frequent
and momentary; the heart having to contract sixty or seventy times per
minute, rests 6∕11 of a second each second, or more than thirteen hours
in the twenty-four. The lungs and respiratory muscles rest a shorter
time than this, but probably about three hours per day.

The necessity for rest is well shown by the sense of taste. If salt
is kept in the mouth for a considerable time, the power of tasting it
disappears, and only returns in its original strength after several
hours. The gustatory nerve has been exhausted.

The other sense-organs illustrate the same principle. Persons are not
uncommonly made deaf by the sounds of machinery. After looking at a
particular colour for some time, the nerves receiving impressions from
this colour are exhausted, and only its complementary colour is visible.

Rest may be either _partial_ or _general_.

The principle of partial rest has very useful practical bearings. Such
rest is illustrated by the student who takes a walk, or uses methodical
gymnastic exercises; a concert may provide agreeable exercise for the
auditory nerves and the part of the brain connected with them, while
allowing the over-tired intellectual part of the brain to rest in
peace; similarly, light literature may prove a pleasing rest after
severer studies.

Walking is more especially the exercise of the brain-worker.

Partial rest is the same thing as _change of occupation_, and by a
careful regulation of the relative amount of cerebral and muscular
work, energy can be largely economised. The horse, which exercises
chiefly his muscles, requires only five or six hours to recuperate his
energy; and our muscles require less sleep than our brain.

=Sleep= is the only form of complete and general rest. In attaining
this condition, the muscles sleep first, then the eyes close (owing to
muscular rest), and the thoughts wander; hearing is the last sense to
lose cognizance of the surrounding world; dreaming succeeds wandering
thoughts, and even dreaming may cease if the brain repose is complete.

During sleep the brain diminishes in size, and becomes paler; the
amount of blood in the brain being diminished. Probably the cerebral
anæmia is rather a consequence of the functional inactivity of the
brain during sleep than a cause of the sleep.

During sleep the heart and lungs continue their work; the blood is
circulated and purified, the intestines continue their vermicular
contractions, and absorb food from the alimentary canal, and the organs
nourish themselves at leisure.

Two facts relating to sleep have important practical bearings. First,
during sleep _metabolism is less active_, and so the temperature of
the body tends to be somewhat lowered. Secondly, _assimilation is more
energetic_; this favours the absorption of noxious vapours, if any
are present. There is probably, therefore, slightly less danger of
remaining in a stuffy, impure atmosphere during the day than at night.

=Practical Rules Concerning Sleep.=—1. _Amount of sleep required._ It
is impossible to lay down any fixed rule applicable to all persons and
circumstances. The amount of sleep required, like the amount of food,
varies greatly.

_Habitual deficiency_ of sleep produces a condition of wretchedness and
prostration, with great restlessness. Prolonged watching inevitably
breaks down the constitution. Not the least evil consequence of
irregular and deficient sleep is, that sleep, when desired, is often
courted in vain.

_Habitual excess_ of sleep produces a condition of brain less active
than usual, and less favourable for thought and action. Impressions
are received less readily, and the power of will is correspondingly

The amount of sleep required varies with—

(1) _Age._—The infant, if healthy, spends the larger part of his
existence in sleep; gradually the amount required diminishes until,
for the adult, seven or eight hours suffice. Children over two or
three years old require sleep only during the night. In advanced life
there is a tendency to revert to infantile habits, sleep occurring in
frequent short snatches.

(2) _Sex._—Women have been stated to require rather more sleep than
men, but this is doubtful. The hours of sleep required have in
accordance with this view been stated to be, “Six for a man, seven for
a woman, and eight for a fool.” A reversal of this order would more
nearly approximate to the requirements of town life.

(3) _Temperament._—Those of a cold lymphatic temperament require more
sleep than sanguine or nervous people, though the latter sleep more
deeply. Frederick the Great, John Hunter, and Napoleon I. are said to
have required only five hours’ sleep per day; but the last of these had
the faculty of taking short naps at a few moments’ notice.

(4) _The sick and convalescent_ require much more sleep than those who
are healthy.

(5) _Habit_ has a very important influence. Many people appear to
sleep too much, and thus dull to some extent their mental faculties;
but on the other hand, modern life, with its nervous strain, keen
competition, and constant hurry and worry may make a larger amount of
sleep necessary than that required by our forefathers, who invented the
foregoing proverb.

(6) _Occupation._—Mental work requires more repose than physical.

2. _Relation of sleep to food._—The molecular life of the tissues—that
is, the processes of nutrition—ought to be undisturbed. These go on
most perfectly when no active function, such as that of digestion,
is being performed. But while the stomach carries on the digestive
functions to only a small extent during sleep, the intestines continue
still to digest and absorb food. In accordance with these facts, it is
advisable to allow at least two hours between the last meal of the day
and sleep, especially if animal food has been taken.

3. As absorption is increased and the temperature is lowered during
sleep, it is important to _sleep in pure air_, and to have _warm
coverings_, especially about the shoulders and arms. Many an obstinate
cough might be cured by the simple expedient of wearing a flannel
jacket at night.

4. _Sleep during the night and not during the day._ It should hardly be
necessary to say this, as the universal instinct of animals shows its
advisability; but, unfortunately, the habits of mankind have commonly
led to a partial reversal of the natural arrangement.

5. The room should be dark; light, like sound, is inimical to sleep.
The head should be moderately raised. The temperature of the room for
robust persons need not be artificially raised.

=Sleeplessness=, as a rule, occurs only when some physiological law has
been broken. To relieve it, it is essential to equilibrate muscular
and mental functions. Increase of muscular exercise is an important
element in its treatment. In addition it is advisable not to have any
severe mental work during the evening, nor to indulge in late suppers.
Sleeplessness is the bane of many men of a nervous temperament, and
chiefly attacks those of sedentary habits. It is apt to recur, and
for this reason, if for no other, narcotics ought to be scrupulously
avoided. The habit of taking such soporifics is unfortunately
becoming much more common, and is productive of many evils. Death
from accidental overdose is a frequent calamity; and, apart from this
possibility, the invalid’s nervous system is completely ruined by
persistence in the habit, his power of will is annihilated, and he
becomes the miserable slave of an evil habit, whose end is death (see
also page 54).



=Physiological Considerations.=—The skin consists of a superficial part
or epidermis, and a deeper part called the dermis or cutis.

Tubes of two kinds open on the surface of the skin, penetrating at
their deeper ends into the cutis, viz. sweat or _sudoriparous glands_
and _sebaceous glands_. The sudoriparous glands are simple tubes,
the lower ends of which lie coiled up in the dermis. Each tube when
straightened out is about a quarter of an inch long. It has been
estimated that in the palm of the hand there are 3,528 orifices
of sudoriparous and sebaceous glands on a square inch of surface;
reckoning each gland at 1∕4 inch long, this means 73½ feet of tubes
in this small space. Assuming that there are 2,800 tubes to every
square inch, and that the amount of surface in a man of ordinary
height and bulk is 2,500 square inches, it follows that there are
seven million pores in a man—that is, 1,750,000 inches, or nearly
twenty-eight miles.

The perspiration secreted by the sudoriparous glands is constantly
evaporating from the surface of the body. It is very important that
the orifices of these glands should be kept open in order that the
secretion may not be interfered with. Animals have been killed by
covering their skin with gelatine, and so preventing the escape of

The sebaceous glands are shorter than the sudoriparous, and commonly
end alongside the hairs before the latter issue from the skin. They
secrete an oily material which serves the purpose of a natural pomade.
The sebaceous secretion also keeps the general surface of the skin
unctuous and supple. The smell of the sebaceous secretion may be
unpleasant, especially in the arm-pits and some other parts. Frequent
washing is therefore desirable.

The =Conditions Due to Uncleanliness= are due to obstruction of the
excretory ducts, to accumulation of _débris_ on the general surface of
the skin, and to the consequent interference with the circulation.

1. The _obstruction_ of the sudoriparous pores of the skin interferes
with the elimination of waste products by the perspiration; these are
re-absorbed or retained in the system; consequently more work is thrown
on the lungs and kidneys, and the equilibrium of health is destroyed.

Sebaceous obstruction causes an accumulation of oily secretion in
the ducts. The black spots so commonly seen about the nose, are the
blocked up orifices of sebaceous glands, and by squeezing the nose
tiny threads of fatty matter are forced out from the interior of
these glands. Pimples on the face are usually due to obstruction of
the sebaceous glands; sometimes the obstruction leads to inflammation
around the sebaceous gland (_acne_) which often permanently injures the

2. _Accumulation_ of effete matter on the skin occurs, unless frequent
ablutions are performed. The epidermis is constantly shedding its older
and more superficial parts, in the form of minute scales or “scurf.”
In the absence of frequent washing, the scales of epithelium tend to
accumulate, the sebaceous secretion matting the scales together, and
rendering them more adhesive. The saline matters of the perspiration
also accumulate along with the scales and sebaceous secretion, and in
virtue of their hygroscopic properties tend to keep the skin clammy and

The obstruction of excretions and the accumulation of _débris_ lead to
other consequences. Thus:—3. The _sensibility of the skin_ is dulled
when the sensory papillæ are covered with dirt. The sensations received
by the skin are important in regulating the temperature of the body.
A cold external temperature should cause a reflex contraction of the
small arteries bringing blood to the skin, thus diminishing the flow
of blood and preventing undue loss of heat. Similarly, if the external
temperature is high, or the internal development of heat is too great,
these arteries dilate, and sending more blood to the skin, cause a
greater loss of heat by radiation and conduction. Impaired sensibility
of the skin leads to imperfect action of the reflex nervous mechanism
to which the above effects are due, and consequently the dangers
resulting from sudden alterations of temperature are greatly increased.

4. The _tendency to chills_ is increased, not only by deficiency of the
nervous tone of the skin, but also by obstruction of the pores of the
skin, and by the hygrometric action of the saline matter collected on

5. _Cutaneous diseases_ are due to, or favoured by, uncleanliness.
These are of two kinds—_parasitic_ and _non-parasitic_. Acne, which is
the chief non-parasitic disease favoured by uncleanliness, has been
already mentioned.

Parasitic skin diseases are greatly favoured by the presence of a
dirty skin, which affords a suitable soil for the development of the
parasites. (See also page 275).

=Uses of Soap.=—Soap is produced by an action of an alkali on an oil.
The alkali displaces glycerine from the oil, and forms an alkaline
stearate, which is soap. Soft soap is chiefly stearate of potassium;
hard soap is stearate of sodium. There may also be present the alkaline
salts of oleic and palmitic acid. Soft soap is not used for washing
the skin, as it is too irritating. All soaps contain a slight excess
of soda; the greater this excess, the more irritating is the soap to
delicate skins. Hard soaps may be also made with potash, if the fat
employed be a solid one; but such soaps are rather softer than ordinary
hard soaps, and more caustic. Cocoa-nut oil is used in making marine
soaps, because, unlike all other kinds, it is not rendered insoluble
by brine, and so will form a lather with sea-water. Normal soaps
contain from 15 to 35 per cent. of water. “Liquoring” a soap consists
in adding 5 to 25 per cent. of soluble silicates. By this means the
soap may be made to hold 70 per cent. of water, which is obviously very

In washing the skin, the water washes away a considerable amount of
epidermis, and the saline matters which have collected. For the oily
sebaceous secretion soap is required. The alkali in soap combines
with the oily matter, forming an emulsion which carries away with it
a quantity of the dirt which previously blocked the orifices of the
sebaceous and sweat ducts. When the skin is rubbed by the towel after
washing, the softened epithelium, and with it any remaining dirt, are
rubbed off, leaving the skin clean, and able to perform its normal

=The Use of Baths.=—The primary object of bathing is cleanliness. A
secondary consideration is the pleasure derived from bathing. Baths are
especially necessary for those persons who lead sedentary lives. When
the skin is kept in an active condition by exercise, it to some extent
cleanses itself. Thus, a farm labourer who has a weekly bath, may be
really cleaner than a person of sedentary habits, who has two baths per

Baths are classified according to temperature as follows:—Below 70°
Fahr. they are described as _cold_; tepid up to 85°; _warm_ up to
97°; and _hot_ over this temperature. It is important in deciding
the temperature of a bath not to trust to one’s sensations; the only
accurate measure is by the thermometer. A cold morning tub in the
summer will commonly contain water at 55° to 60°; while the same in
winter will be down to 40°, or occasionally to 32°.

For purposes of cleanliness the _warm bath_ is the most efficient,
combined with the free use of soap. The chief objection to it is that
it produces an increased flow of blood to the skin, by relaxing the
cutaneous blood-vessels, thus increasing the danger of chills if there
is subsequent exposure. The increased sensibility to cold resulting
from a warm bath may be obviated by afterwards rapidly sponging the
body all over with cold water, and then drying the body quickly, and
using the friction of a moderately rough towel. It is desirable for
both cold and warm baths to have a “bath-sheet,” in which the person
may be completely enclosed on coming out of the bath. Drying is thus
much more quickly accomplished, and the danger of chill is minimised.

A daily morning _cold bath_ is a most important agent in the
maintenance of robust health. The first sensation on entering a cold
bath is of shock, due to the cooling of the surface of the body. This
is followed in a few seconds by a glow, due to the blood returning
with considerable force to the skin. A cold bath ought to be taken
as rapidly as possible. If soaping the body is desired, it should be
done before entering the bath, and the stay in the latter should be
little more than momentary. In this way the best reaction or “glow” is

If a feeling of cold and chilliness remains after a cold bath, it has
done more harm than good. This condition may often be avoided by
quick drying and brisk friction; if after this a good reaction is not
obtained, the temperature of the water should be increased. For those
who are not very robust, the “cold tub” in winter is to be deprecated.
If the water be raised to 60° by the addition of warm water, or in some
cases even to 70°, a good reaction may be obtained. In other cases, in
which a reaction is not experienced even after a bath of the latter
temperature, a tepid bath may be taken, and then the body rapidly
sponged with colder water.

Cold baths increase the tone of the skin, rendering it less susceptible
to changes of temperature. The tendency to “catch cold” is diminished,
the blood-vessels and nerves of the skin both responding more readily
to any stimuli.

_Swimming_ is a valuable combination of bathing and exercise. A sudden
plunge into cold water for swimming purposes is dangerous to those
who are not hardened to it, and especially so in the case of running
water, as in rivers or the sea. Here the water around the swimmer is
constantly being changed, and each layer of water coming in contact
with him abstracts a considerable amount of heat. Many of the cases
of so-called death from “cramp” are really due to the benumbing and
depressing influence of continued cold on the vital organs.

Swimming, under proper superintendence, ought to be universally
enforced. The exercise accompanying it serves in most cases to
counteract the depressing action of the cold water; but it is important
in all cases to attend to certain rules. The immersion should not be
prolonged; the body should be warm at the time of entering the water;
and the bath should not be taken until about two hours after a meal;
nor after prolonged fasting, as before breakfast.

=Personal Cleanliness.=—Personal cleanliness involves not only
attention to the skin, which we have already considered, but to the
hair, nails, mouth, and other parts of the body.

The _hair_ ought to be carefully brushed and combed, but it is not
desirable to use soap to it as often as to the skin. Soap removes the
sebaceous secretion from the hairs, and renders them dry and brittle.
Artificial pomades are, as a rule, unnecessary.

The _nails_ should be cut square, and not down at the sides. It is
hardly necessary to say that they should be kept clean: they may convey
serious infection.

The _mouth_ and all mucous orifices should be kept scrupulously
clean. A fœtid breath is not uncommonly due to the discharges from
carious teeth, or to the decomposition of food which has been allowed
to accumulate in the cavities of teeth. Such decomposing matters
when swallowed, are apt to produce indigestion; and this also occurs
from imperfect mastication of food by the bad teeth. It is important
that the _teeth_ should be frequently cleansed, and that all carious
teeth should be “stopped” at an early period, and tartar and other
accumulations removed. Whether bad teeth, which are so extremely
common, are due to the drinking of very hot liquids, or to the fact
that the more perfect cooking of food gives less healthy friction
to the teeth, is doubtful. Whatever the cause, by keeping the mouth
thoroughly sweet and clean, and by having the carious teeth stopped
as soon as discovered, their vitality may be greatly prolonged. Teeth
should be periodically inspected by a competent dentist. Irregularities
of the teeth may be corrected, if they receive early attention. Carious
“milk-teeth” should receive attention from a dentist, as well as the
permanent teeth.

=General Cleanliness.=—Next to cleanliness of the skin, that of the
_apparel_ is most important.

There is a general preference for colours “that do not show the dirt”;
the fact that it is still there, though not seen, being partially
ignored. Changing of apparel is commonly confined to underclothing.
It is forgotten that vests, trousers, dresses, etc., acquire a large
amount of dirt and organic matter, and ought to be changed and well
aired at intervals.

Cleanliness in respect to _bedclothes_ is very important. Organic
matters evolved from the skin, lungs, etc., hang about the bed-linen,
and give the bedroom the “close smell” which can be perceived on
entering it in the morning straight from the fresh air. The beds
should not be made directly after being evacuated, but the clothes
should be thrown over the bottom of the bed, the bolsters and mattress
well shaken, and every part exposed to a free current of air during
the greater part of the morning, before re-arranging the clothes.
Eider-down quilts, unless frequently ventilated by exposure to outside
air, are unwholesome. Superfluous bedroom furniture should be avoided,
as it all takes away from the breathing-space. Bed-hangings should be
reduced to a minimum, and all excretory matters covered up during their
stay in the room, and removed as early as possible.

Cleanliness of _the house_ is also very important as a means of health.
Dust, in however obscure a corner it rests, attracts to itself organic
matters, and forms a soil in which disease germs may grow. Besides
this, it devitalises the air, depriving it of its active oxygen. (See
also page 101).

Dust in _the streets_ serves to carry about various diseases, besides
mechanically irritating any part it comes in contact with, producing
bronchitis, etc.



=Physiological Considerations.=—The average temperature of the surface
of the body in man is 98·4 to 98·6°. The maintenance of a tolerably
uniform temperature is an essential condition of life. The factors
governing the temperature of the body are _the amount of heat produced_
and _the amount lost_. If more heat escapes, more has to be generated;
and the source of all the heat produced in the body is the food taken.
This becomes changed by the metabolic processes occurring in the body
which produce heat.

=Heat is lost=, (1) by the _skin_; (2) in _respiration_, the expired
air having been heated during its stay in the lungs; (3) with the _food
and drink_ taken, if not at the temperature of the body; (4) with the
_excreta_; and (5) by transformation of heat into _mechanical energy_.
Of the whole loss by these different channels, probably eighty to
ninety per cent. is through the skin.

=The Loss of Heat by the Skin= is in three different ways. First, by
_conduction_, when the skin comes in contact with anything cooler
than itself; secondly, by _radiation_ into space; and thirdly,
by _evaporation_ of the perspiration. The last cause produces a
considerable reduction of temperature, even when the perspiration is
not so abundant as to be visible, but is in the form of insensible
perspiration. The losses by these different sources vary in amount;
when one is increased, another is diminished, by way of compensation.
Thus, in very cold weather, the amount of radiation and conduction
of heat are increased; but evaporation greatly decreases, and the
diminished loss of heat in this respect counter-balances in some degree
the increased loss by radiation and conduction.

When the external warmth is considerable, increased evaporation occurs;
while when the weather is cold, the cutaneous arteries contract, and
less blood goes to the skin, and so the loss of heat is diminished.
In most climates, however, this action of the skin requires to be
supplemented by some kind of clothing.

=Requisites of Dress.=—1. The first and most important requirement is
that _clothing should maintain a uniform and equable temperature_ in
all parts of the body.

In hot climates clothes are required in order to protect the body
from external heat. In this country, they are required to prevent the
too rapid escape of heat from the body. For both these purposes,
dress must be of a non-conducting material, in order not to encourage
transfer of heat into or from the surrounding atmosphere.

The loss of heat by the skin may be prevented by interfering with
radiation or conduction of heat, or with evaporation from its surface.
Radiation of heat from the skin is prevented by clothing, the dress
taking the place of the skin as a radiating surface. The amount of
radiation from the dress will depend on the rapidity of conduction of
heat from the skin. The amount of conduction and of radiation of heat
will vary considerably with the _material_ and _colour_ of the dress.

As regards =conductivity=, the two extremes are represented by linen
and fur. It is found that if the conducting power for heat of linen =
100, then that of wool = 50 to 70. This partly explains why woollen
goods are so much warmer than linen. We shall find that there is
another explanation in the relative hygroscopic properties of the two

As regards =radiation= of heat, in one experiment it was found that
while a piece of linen took 10½ minutes to cool, a corresponding
piece of flannel took 11½ minutes.

Apart from the material, the =colour of dress= has some influence
in regulating the loss of heat. Dark-coloured materials absorb more
light and heat than lighter coloured materials; they may be good or
bad conductors of heat, according to the nature of the material. White
reflects the rays of light and heat; hence it is a poor absorber. In
summer it prevents the passage of heat inwards, and, in winter, may
prevent its passage from the body. It is thus well adapted for both
winter and summer clothing, and has the additional advantage of being
the cleanest colour.

Franklin placed a number of squares of different coloured cloths of the
same material on snow, and found after a time that the snow covered
by the black piece was most, and by the white piece least melted. In
another set of experiments, shirting materials dyed various colours
were taken, and it was found that if the rays of heat received by white
were represented as 100, pale straw received 102, dark yellow 140,
light green 155, Turkey red 165, dark green 168, light blue 198, black

The influence of colour is antagonised to a large extent by the nature
of the material; the increased heat absorbed by a dark material may
be counterbalanced by the material being a good conductor. Also the
influence of colour is only exerted superficially; hence, although it
produces considerable effect in thin textures, as gauze, it has little
influence on thick materials.

2. _The dress should not interfere with perspiration._ In order that
it may not do this, it should be competent to absorb moisture easily,
without its surface becoming wetted. Materials like linen which lose
their porosity and rapidly become wetted by perspiration, cause rapid
loss of heat from the body, inasmuch as water is a better conductor of
heat than air. Pettenkofer found that while the maximum hygroscopic
power of wool (flannel) is 174 and the minimum 111; the maximum of
linen is 75 and the minimum 41. Hence, with a flannel vest next the
skin, the liability to chill is much less than with a linen one. There
is one slightly counterbalancing drawback; hygroscopic materials absorb
moisture from the air, as well as from the skin. A woollen coat during
a damp day, without rain, increases considerably in weight.

Waterproof clothing is injurious when worn beyond a short period, on
account of its being non-porous and consequently keeping the body
enveloped in a vapour bath composed of its own perspiration. For a
similar reason India-rubber boots are objectionable, except for short
periods; they make the feet damp, and even sodden. Sealskin jackets
are objectionable for walking, not only because of their weight, but
because they are not porous.

3. _The warmth of clothing should be uniformly distributed_ throughout
the body. This principle is very frequently departed from; and
consequently one part may be chilled while another is over-heated.
This is seen especially in female apparel. The same evil is seen in
the short sleeves, and short and low-necked dresses of young children.
“Combination” garments for women, and sleeves and leggings for young
children are happily becoming more generally adopted, and will diminish
the diseases due to exposure to cold.

4. _The clothing should not be tight_; and this for three reasons.
First, because _loose clothing is warmer_ than tight; this everyone
has experienced in the case of gloves. The retention of air in the
meshes of clothing is one of the main causes of its warmth, air being
a bad conductor of heat. The imprisonment of air in the meshes of the
material largely explains the warmth of eider-down quilts, furs, and
flannels as contrasted with linen.

Secondly, clothing should not be tight, in order _to avoid interference
with the action of the muscles_. Tight sleeves prevent the muscles of
the arms and chest from being exercised. Tightly laced corsets imprison
the trunk muscles, prevent their contractions, and so lead to muscular
weakness and occasionally spinal curvature. Tight skirts similarly
prevent free play of the lower limbs, leading to a halting gait, a
diminished amount of exercise, with all the evils following deficient
exercise. Tight clothing is not confined to one sex, and in all cases
leads to hampered movements and deficient muscularity.

Thirdly, tight clothing tends to _impede the functions of circulation,
respiration, and digestion_. The fashion which more than any other
interferes with important functions is _tight-lacing_. This produces
(1) compression and displacement of the viscera; the liver and the
stomach especially suffer. (2) Respiration and circulation are impeded,
the action of the diaphragm being impeded. (3) The muscles of the trunk
being tightly encased, are incapable of movement, and consequently
tend to waste and atrophy. The general outline of the body is altered.
Instead of the waist being elliptical, as it naturally is, it becomes
nearly circular; and instead of its circumference averaging twenty-six
to twenty-seven inches, it may be eighteen to twenty-one inches. Tight
_garters_ tend to produce varicose veins.

_Tight boots_ are injurious, as they tend to destroy the natural
elasticity of the movements, and confine them within narrow limits.
They act to some extent the part of splints. By interfering with the
circulation of blood through the feet, they cause cold feet, and not
uncommonly chilblains. _High-heeled boots_ do not allow the natural
elasticity of the foot to come into action. They distort the movements
of the body and cause corns and bunions. Similar effects are produced
by boots which are too narrow and have pointed toes, thus not allowing
free movement of the toes.

5. _The weight of the clothing should be the smallest amount consistent
with warmth, and it should be evenly distributed._ The chief weight
should not be suspended from the waist, as here the parts are not
well supported by bones. The shoulders and hips should share in the
suspension of clothing, thus diminishing the danger of compression and
displacement of internal organs. In order that garments may be as light
as possible, they should be made to fit to each limb separately, thus
diminishing the amount of material required.

6. _The materials of dress should be as far as possible
non-inflammable._ This may sometimes be disregarded, but is often
important, as in the nursery. In this respect, as in many others,
wool possesses great advantages. Woollen fabrics smoulder rather than
burst into flames, and thus the injury resulting from any accident is
limited. Cotton is more inflammable than linen, linen than silk, and
silk than wool. A closely woven cloth is less inflammable than one with
open meshes.

Dress materials, and more particularly muslin, have been rendered
non-inflammable by treating with a solution of ammonic phosphate,
or ammonic phosphate and ammonic chloride mixed. The best material,
however, is sodic tungstate, which, unlike the others, is not affected
by ironing. Sodic molybdate is used in arsenals to render the workmen’s
clothing non-inflammable. All the above plans are objectionable, as
the weight of the material is increased 18 to 29 per cent., and they
all wash out. To remedy this, a “fire-proof starch,” containing sodic
tungstate has been devised.

Perfect non-inflammability is only required in certain dangerous
occupations. The plans hitherto mentioned simply prevent the fabric
breaking out into flame. The only cloth absolutely unaffected by fire
is asbestos cloth.

7. _Elegance of dress_, although not so important as utility, is not to
be neglected, and the two are perfectly compatible. In fact, elegance
is indirectly associated with utility, for nothing which is awkward,
or leads to obstructed movements or distortions of the body, is really
elegant. A sudden constriction, as in a very tight waist, is not only
bad from a hygienic point of view, but is also ugly.

=Materials for Clothing.=—The materials used are derived partly from
the vegetable world, as hemp, flax, cotton; and partly from the animal
world, as silk, wool, hair, feathers. The most important materials are
wool, silk, cotton, and flax.

1. _Wool_ varies somewhat in character, according to the animal from
which it is derived. In all its varieties, however, it preserves the
character of a bad conducting and porous substance, the two most
important requisites in a dress material.

(1) Wool from the sheep is really a soft and elastic hair, composed of
fibres three to eight inches long, and about 1∕1000 inch thick. The
finer and shorter wools are used for fine cloth, the longer and coarser
for “poplins,” “worsted pieces,” etc. Flannel is a woollen stuff of
rather open and slight fabric. Wool is irritating to delicate skins,
and may be so much so, that it cannot be worn next the skin, whether
as flannel, worsted, or merino. In these cases, it may be worn outside
a linen or gauze vest, and so all its advantages secured. It is one of
the worst conductors of heat, and ought always to be worn in winter;
while even in summer, it ensures a greater immunity from chill after
perspiration than any other material.

(2) _Cashmere_ is made from the down found about the roots of the hair
of the Thibet goat. Imitation cashmere is made of various materials
mixed together.

[Illustration: FIG. 56.


(3) _Alpaca_ is obtained from the fleece of the llama, alpaca, and
vicuna. It is longer than the fleece of the sheep, the fibres, which
are soft and strong, averaging six inches in length. It is commonly
made up with cotton or silk.

(4) _Mohair_ is the hair of a goat inhabiting the mountains near
Angora. It is woven into an almost waterproof cloth, and used in making
plush, braid, etc.

2. _Hair_ derived from the horse or cow differs from the hair usually
called wool, in the greater solidity of its structure, which makes it
ill adapted for clothing. Its chief use is in the manufacture of felts,
of which hats are made.

3. _Leather_ is a kind of natural felt, very close and firm in its
texture. It is used in this country chiefly for boots, but in some
colder climates also for coats, etc. It is impervious to moisture, like
sealskin, and is consequently not very healthy. The same objection
applies to _chamois-leather underclothing_, which is non-porous,
and consequently keeps the skin hot and clammy; also, it cannot be
washed without becoming stiff on drying. This necessitates wearing the
material after it has become impregnated with perspiration.

4. _Silk._ The thread spun by the silk-worm is composed of filaments
1∕2000 inch wide, and is the strongest and most tenacious of textile
fabrics. Its thread is three times as strong as a thread of flax of the
same thickness, and twice as strong as a thread of hemp.

Its fibres are round like those of linen, but softer and smaller; it
gives an agreeable sensation of freshness to the skin even more than
linen. It is a worse conductor of heat than cotton or linen. Its great
disadvantage for wearing next the skin, apart from its expense, is that
it irritates delicate skins. _Satin_ is silk so prepared as to form a
smooth, polished surface.

_Velvet_ is a silk fabric of which the pile is due to the insertion of
short pieces of silk thread under the weft or cross-thread. Cheaper
kinds are made, containing a certain proportion of cotton.

_Crape_ is made of raw silk gummed and twisted to form a gauze-like
fabric. Taffety, moire, brocade, and plush are made of silk alone or
combined with cotton.

5. _Cotton_ consists of the downy hairs investing the seeds of the
gossypium plant. The threads of which it is composed are flat,
ribbon-like, and twisted, about 1∕800 to 1∕2000 inch wide. Owing to its
flat fibres with sharp edges, it is apt to irritate delicate skins;
linen is preferable for dressing wounds for a similar reason. Cotton
is warmer than linen, being a worse conductor of heat. It also absorbs
moisture better, not becoming wet so soon; but it lacks the “freshness”
which makes linen materials pleasant to wear. Calico, fustian, jean,
velveteen, and muslin are the chief cotton fabrics.

6. _Flax_ is formed from the fibres of the flax plant. Linen is made
from it. Cambric and lawn are very fine and thin linen materials. The
fibres of linen are round and pliable; thus it is smooth and soft, and
peculiarly agreeable to the skin. It is, however, a good conductor of
heat, and consequently “it feels cold” to the skin. Furthermore its
pores quickly become filled with perspiration, which escapes rapidly,
thus chilling the body.

7. _Mackintoshes_ are valuable as a temporary protection against
external wet. Worn for more than a short period, they produce great
heat and a sense of closeness, owing to retention of the perspiration.
The best form of mackintosh is one having a cape, with a space for
evaporation between it and the rest of the garment.

=The Amount of Clothing required= varies with circumstances. 1.
_Health_; those of robust constitution require less than the feeble.
The more active are digestion and assimilation, the less is the amount
of clothing required. If heat is preserved by clothing, less food is
required. Thus a distinct saving of food is effected by warm clothes.
Warm clothes are the equivalent of so much food that would have been
required to keep up the temperature of the body, if the clothes had not
been worn. Thinly clad persons under conditions of starvation die more
quickly than those who are better protected.

2. Clothing requires to be adapted to _climate and season_. In winter
and in cold climates the amount of clothing must be increased, and
warmer materials chosen. In the changeable climate of Great Britain, it
is difficult to adapt the character of one’s dress to the requirements
of the weather. _Clothing ought, however, not to be changed according
to the calendar_, but according to the weather. The tendency is to
assume summer clothing too early in the spring, and to continue it too
far into the autumn. According to Boërhave, winter clothing should be
put off on Midsummer day, and resumed the day after. This, although
rather exaggerated, may serve to impress the caution required. The same
authority says that only fools and beggars suffer from cold, the latter
not being able to procure sufficient clothes, the former not having the
sense to wear them.

3. _Age._ Those at the two extremes of life are specially susceptible
to cold. The mortality of infants during the first three months of
life is nearly doubled in winter. Bronchitis and pneumonia prove fatal
chiefly at the two extremes of age.

The younger a child the larger is its surface as compared with its
bulk, inasmuch as the area of a body varies as the square of its
dimensions, while its mass varies as their cube. Thus a cube 1 inch
each side has 6 square inches of surface to 1 cubic inch of bulk, while
a cube 10 inches each side has 600 square inches of surface to 1000
cubic inches in bulk. Similarly a child 1∕10 the size of its mother,
besides its feebler powers of producing heat, has ten times as much
surface in proportion to its size by which heat is lost.

After the age of thirty-five, it is better to exceed than to be
deficient in clothing. A degree of cold that would act as a useful
tonic to the robust and middle-aged, produces serious and even fatal
depression of the vital powers in children or aged people. For the same
reason it is advisable to discontinue cold baths as age advances.

A very pernicious delusion is prevalent, that children ought to be
“hardened” to the influences of cold, and that too much clothing “makes
them tender.” Excessive clothing may possibly increase the tendency
to “catch cold,” owing to its exciting perspiration, or owing to the
fact that the extra clothing is commonly thrown off at irregular
intervals—witness the effects of wearing a scarf round the neck
occasionally. But to suppose that children can be hardened by exposure
of arms and legs, and other parts of their bodies, is irrational.
A large amount of heat is lost from these bare surfaces, and apart
altogether from the danger of chill, more food must be taken to
compensate for this loss of heat, and keep up an equable temperature.
Also if the food taken is expended in preserving the warmth of the
unprotected body, less material is left for the purpose of growth. From
these causes it frequently happens that children remain stunted in
growth, even if latent disease is not actually developed by the extra
strain on their resources.

The children of the very poor are often pointed to as demonstrating the
power of hardening. It is forgotten how many of these poor children
have perished under the hardening system, and that the good health of
those remaining is in spite of the hardening.

=Poisonous Dyes in Clothing.=—These, like poisonous wall-papers, were
formerly much more common than at present, and, as in wall-papers, the
poisonous agent has most frequently been arsenic, large quantities
of which were formerly used in the preparation of certain dyes.
Occasionally such poisonous pigments are still employed.

The means of detecting arsenic in any fabric or wall-paper are given on
page 216.



=Parasites= (Greek, _para_, upon, and _siteo_, I feed), in the broadest
sense of the word, are living organisms, which derive their nourishment
from other living organisms. They may belong to the vegetable or
animal kingdoms, and may live on the skin, in the alimentary canal,
or in some one of the internal organs. Some, like the fungus causing
ringworm, feed on the living tissues of the animal infested; others,
like tape-worms, on the partly digested food; while other parasites,
like fleas, only pay temporary visits to the surface of the body, for
the purpose of obtaining food.

=Vegetable Parasites.=—Vegetable parasites all belong to the class of
fungi, and more accurately to the two lowest divisions of this class
which have been provisionally formed, viz.—Schizophyta, and Zygophyta.
The Schizophyta include two orders, =Schizomycetes= and Saccharomycetes.


=Bacterium= is the generic name given to the micro-organisms
belonging to the schizomycetes, whether a bacillus (rod-shaped),
coccus (rounded), spiral-formed (spirillum or vibrio), or filamentous
(leptothrix and spirochœta). All these are destitute of chlorophyll and
multiply by fission.[9] They are all extremely small, the width usually
not exceeding 1 µ = 1∕25000 inch. Various names are given to them,
which are synonymous, thus: germs,

  bacteria (_singular_ bacterium).

When they cause disease they are called _contagia_. They multiply
rapidly, and may reach maturity in 20 to 30 minutes. One bacterium may,
under favourable conditions, become 16,000,000 in 24 hours.

=Methods of Examination.=—Until Koch discovered the method of
cultivating bacteria on solid media, the science of bacteriology
remained in its infancy, as it was impracticable to obtain pure,
_i.e._ unmixed cultures of a given bacterium. Koch hit on the idea
of mixing minute portions of cultivations of bacteria which were
growing in liquid broth with liquefied gelatine, and then spreading the
mixture on glass plates, and allowing it to solidify under cover, so
that no atmospheric bacteria could contaminate the growth. When this
was done, individual bacteria formed individual “colonies” scattered
over the gelatine, and these could be identified by sub-culturing and
other methods, for the details of which books on bacteriology must be

The _food supply_ of most bacteria is vegetable or animal refuse.
Some of them have a most useful purpose in nature, that of breaking
down complex organic substances and reducing them to a simpler form.
Thus bacteria play an essential part in purifying the soil, and in
the operations in sewage tanks and on sewage farms (pages 192, 195
and 220). A thimbleful of ordinary garden soil which has received a
periodical manurial dressing contains one to three million bacteria.
Certain bacteria have been found to be capable of exercising an
opposite effect, _i.e._ fixing the atmospheric nitrogen and building
it up into the nitrogenous tissues of plants. Thus the nodules on the
roots of leguminous plants consist of bacteria living in symbiosis
with the protoplasm of the plant and supplying it with nitrogen in an
assimilable condition. Pure cultures of these bacteria have been put on
the market as _nitragin_, for enriching land poor in nitrogen. Thus a
fairly complete cycle of nature is secured, and by rotation of plants
(legumes alternating with other seeds), manures, especially nitrogenous
manures, may be partially saved.

The _souring of milk_ is caused by the _bacillus lactis_. This souring
is an indispensable preliminary to the making of cheese, and the
bacillus can now be used in pure culture to hasten the natural process.
The peculiar aroma of good butter is due to a bacterium which has been
isolated; and it can now be supplied in pure culture for butter-making,
thus obviating bad butter.

Certain bacteria are disease-producing or =pathogenic=. The largest
of these is the _Bacillus of Anthrax_, a disease common in sheep and
oxen, and sometimes communicated to man. This bacillus is 1·2 µ thick
and 6 to 8 µ long. When an animal dies of this disease it should be
buried without cutting the skin. When exposed to the air this bacillus
forms minute spores, very difficult to destroy. They may live for
several years in pits in which animals dying from anthrax have been
buried. Butchers have died when inoculated through cracked fingers
when dressing the carcase of a cow which has had anthrax. Similarly
men handling the hides of such animals may be inoculated, either
with a form of disease in which rapid blood-poisoning is produced,
or with a malignant carbuncle, from which recovery is possible if it
be treated promptly. Wool sorters of mohair wool are very liable to
suffer from a fatal form of pneumonia due to the dust from wool derived
from animals which have died from anthrax (page 107). This disease
gives a good instance of possible _attenuation of virus_, of which
another example is seen in small pox (page 293). Pasteur grew anthrax
bacilli in broth at a temperature of 110° Fahr. At this temperature
the bacilli multiplied by division, and no spores were formed. By
repeatedly sub-culturing after the bacilli had become old (_i.e._ by
putting minute quantities of the growth into fresh broth) and exposing
to air, he obtained anthrax bacilli which were only slightly virulent,
only producing slight constitutional disturbance when inoculated,
_i.e._ injected under the skin of sheep, and yet protected them against
ordinary infection by anthrax. Other methods of attenuation of virus
have been discovered. For instance the growth of the bacillus in the
presence of a feeble antiseptic, or passing it through the circulation
of an animal which is relatively insusceptible to the particular
bacillus has this effect.

Other important pathogenic bacteria will be considered later (pages
298 to 398). It is only necessary here to mention that suppuration,
erysipelas, puerperal fever, and a number of forms of blood-poisoning
are due to the invasion of the system by =cocci=. A single round
cell (commonly not more than 1∕25000 inch in diameter) is called
a _micrococcus_. When in pairs as in the micro-organism causing
pneumonia they are called _diplococci_; when in chains, _streptococci_
(_i.e._ twisted); when in masses, _staphylococci_. When cocci and
other micro-organisms are kept out of wounds, healing occurs without
suppuration; this is the principle of the antiseptic and aseptic
methods of treating wounds (pages 106 and 110). The question of
immunity is discussed on page 288.

=Saccharomycetes= occur in fermenting substances, as in the
fermentation of saccharine solutions. The only organism belonging
to this order, which is associated with diseased conditions, is the
_Sarcina Ventriculi_. This is found occasionally in the vomit or even
in the urine of some persons.

The =Zygophyta= occur as thread-like growths, forming a mycelium. This
is composed of jointed branching tubular cells, in which minute spores
are produced. Each spore, when liberated from its tube, is capable of
producing another mycelium, and thus the growth spreads. The spores
may be carried through the atmosphere, thus producing infection at a
distance. They have an average diameter of 6 µ = about 1∕4000 inch.

The following are the chief Zygophytous parasitic diseases:—=Thrush= is
associated with the growth of a minute filamentous fungus, the _oidium
albicans_. It is common in babies, who are improperly fed, and in old
people, or in persons exhausted by any chronic disease. Small white
patches collect on the tongue and neighbouring parts, and these are
often followed by the formation of minute ulcers. When it occurs in
children, the food must be carefully attended to, and feeding bottles
frequently scalded, etc.

=Ringworm= is due to the growth of a large spored or a small spored
fungus (known under the names of _Microsporon Audouini_; _Trichophyton
megalosporon endothrix_, _Trichophyton megalosporon ectothrix_) which
attacks the skin. It is most difficult to eradicate when it occurs in
hairy parts, as the growth penetrates to the roots of the hairs, and
continues to live here long after it has been destroyed on the general
surface of the skin. The fungus spreads on the skin in gradually
enlarging circles, forming rings with a slightly raised margin. It is
extremely contagious, being especially apt to spread in schools. The
spores may be carried about by means of hats or bonnets, by gloves,
towels, razors, and other means. The disease often remains undetected
for some time; and many cases, especially where the scalp is affected,
remain contagious after they have been apparently cured.

The removal of ringworm, as of all other skin parasites, is effected by
some local parasiticide. Prolonged treatment, including the pulling out
of diseased hairs, is required for ringworm of the scalp. A special cap
should be worn, when the patient mixes with others.

=Favus=, or “scald-head,” is due to the growth in the skin of a minute
fungus called the _Achorion Schönleinii_, which invades the same parts
as those affected by ringworm, but differs in its mode of formation
of spores; yellow cupped discs from 1∕4 to 1∕3 inch in diameter being
produced. It is very rare in England, and almost confined to persons
(especially children) who are kept in a filthy condition. It is a
common and fatal disease in mice. The treatment is similar to that of

=Tinea versicolor= is caused by the growth in the epithelial cells of
the skin, of a fungus called the _microsporon furfur_, which, unlike
the two last, does not invade the hair or nails. It forms light brown
patches covered with a horny scurf, which gradually spread, until
nearly the whole trunk may be covered. It does not attack children, and
never affects uncovered parts of the body. It chiefly occurs in those
who do not take frequent baths, and who perspire freely. It can be
removed by daily washing with soap and water and rubbing with a rough
towel, followed by the application of a weak carbolic lotion.

=Animal Parasites.=—Animal parasites are found on the skin or in
internal organs or in the blood or lymphatic vessels. The following are
the most common:—

The _Acarus Scabiei_ is a minute animal not unlike a cheese mite, which
causes the disease known as =scabies= or the itch. It is probably
never more than 1∕77 of an inch in length. The female has eight legs,
with terminal suckers on the four front legs and hairs on the hind
legs. The male is smaller than the female, and in the adult condition
the two hindmost legs have suckers, as well as the four anterior. It
remains on the surface of the skin, while the female burrows deeply in
the substance of the epidermis. At the bottom of the oblique burrow
it deposits ten to fifteen or more eggs, which hatch in a fortnight
and then commence similar operations on their own account. Scabies
generally starts between the fingers, whence it rapidly spreads. The
disease is acquired from some patient suffering from the disease, or by
contact with his apparel. It may become very severe when suspicion as
to its parasitic character has not been entertained. Formerly it was
called “the seven years’ itch,” from the great difficulty in curing it
before its true cause was discovered.

The irritation caused by the insect produces eczema, and this may be
thought to be the only disease present, unless careful examination is
made for the burrows of the insect.

To remove this parasite, first the skin is softened, the superficial
epidermis is removed, and the burrows are laid bare, by the daily
use of hot baths with soft soap, and subsequent rubbing with flesh
towels. Then some parasiticide, such as the well known sulphur
ointment, is rubbed into all the affected parts of the skin. A few
days’ perseverance in this treatment usually suffices for a cure. The
patient’s clothes and bed clothes ought also to be thoroughly purified
by boiling or by steam disinfection or by baking in an oven; otherwise
he may become re-infected.

The =Larvæ= of several insects have been found embedded in the skin. In
the ox, the larva or bot of the gadfly produces a troublesome disease,
a large boil being formed under the skin as the larva grows. This larva
has, on rare occasions, attacked human beings. Rare cases are recorded
where other larvæ have become developed in men, in all upwards of
twenty separate kinds of insects having been recognized. The treatment
consists in removing the parasite.

The =Chigoe=, commonly known as the jigger or sand-flea, is a minute
parasitic insect, found in the West Indies and northern parts of South
America. It is so small as to be scarcely visible; but the impregnated
female possesses a proboscis, by means of which it penetrates the skin
generally near the nails and there develops a bladder the size of a
pea, which sets up severe inflammation. To get rid of the intruder, the
orifice by which it entered must be dilated with a needle, until large
enough to admit of its extraction, without rupturing the cyst.

Several species of =Fleas= infest the human frame. They are propagated
by means of eggs, the worms from which enclose themselves in a tiny
cocoon before assuming the adult form.

Three varieties of =Lice= occur on the human skin. The first
(_pediculus capitis_) infests the head, especially of children, and
multiplies with astonishing rapidity, the female laying altogether
about fifty eggs. The other two varieties are the body louse
(_pediculus corporis_) and the crab louse (_pediculus pubis_).

Strict attention to cleanliness is the best means of getting rid of
fleas and bugs. A wash made of carbolic acid and vinegar painted over
bed crevices is very efficient. Lice may be removed from the head by
cutting the hair short, and carefully cutting out any hairs to which
_nits_ are attached. The nits are cemented to the shafts of hairs.
Washing the hair with methylated spirit or paraffin is also helpful in
removing them. Afterwards the use of white precipitate ointment will
prevent their re-appearance.

The =Trematoda= or Flukes furnish two human parasites, viz. the
liver-fluke (_Distoma hepatis_), and the Bilharzia hæmatobia. The
liver-fluke occasionally produces jaundice in man. In sheep it is the
cause of the disease known as the “rot.” The _Bilharzia hœmatobia_ is
chiefly found in Egypt, and the Cape Colony. It is about a quarter of
an inch long, and infests the blood vessels, more particularly of the
kidneys; setting up severe irritation and the discharge of blood. It is
probable that the eggs of this parasite are received in drinking water
or on salads, though occasionally inoculation may occur through the
skin when bathing.

The family of =Nematoda= possesses numerous parasitic members. The
common thread worm (_Oxyuris Vermicularis_) is one of the most common
of these. The female is 1∕3 to 1∕2 inch in length, and inhabits chiefly
the lower bowel. The ova, which are from 1∕490 to 1∕1100 inch in
diameter, often gain access to drinking water, or are carried by flies,
or received on salads, etc. The injection of salt and water into the
bowel, and treatment tending to improve the general health, are the
proper remedies.

The round worm (_Ascaris Lumbricoides_) inhabits chiefly the small
intestine; hence medicines for its removal require to be given by the
mouth. The female is from 10 to 14 inches long; the ova, of which each
female discharges on an average 160,000 daily, are from 1∕340 to 1∕440
inch in diameter.

The whip-worm (_Trichocephalus Dispar_) is a smaller nematode, which
is rarely met with in this country. The _Dochmius Duodenalis_ is met
with chiefly in Italy and Egypt. It sucks the blood in the intestine,
causing dangerous anæmia. The =Strongylus Gigas= is chiefly found in
the kidneys of the ox, dog, etc., and is very rare in man. It resembles
a very large round worm. In the kidney it produces severe disorders.
How it gets there is not known.

The _Trichina Spiralis_ has been already described (page 23).

The _Filaria Dracunculus_ (Guinea Worm) seems to gain access into the
stomach along with water, or possibly in some cases, by perforating the
skin. It burrows among the tissues, especially of the legs, and attains
a length of several feet. It causes large boils and sores, and through
these the eggs escape and pass into water. Here the embryo which has
escaped from the egg meets with a fresh water crustacean (_cyclops_),
enters its body, undergoes larval growth, and is swallowed with its
host by a man, in whom it burrows and undergoes its next stage of life.

The embryos of three species of =Filaria= infest the blood of man,
chiefly in the tropics. One embryonic species is found in the blood
of infested patients by day, one by night, and one during both day
and night. The length of the embryos varies from 1∕75 to 1∕125 inch,
and its width from 1∕3000 to 1∕3500 inch. The night embryo, which is
the most common, is produced by the _Filaria Bancrofti_. This adult
worm infests the lymphatic system of man, sometimes reaching a length
of three to four inches. Its embryos may obstruct lymphatic vessels,
causing obstruction of the flow of chyle (hence originates _chyluria_),
and _elephantiasis_, in which enormous swelling of the legs and other
parts ensues.

The nocturnal migration into the lymphatic vessels, and thence into
the blood of the embryo of the _F. Bancrofti_, is an adaptation to
the nocturnal habits of a particular mosquito (_culex pipiens_ or
_ciliaris_). When the mosquito bites an infested person, his proboscis
removes some embryo filariæ, which are quickly transferred to its
stomach. Some of these escape digestion, develop within the mosquito,
and when the mosquito dies in water they bore their way out, and are
subsequently swallowed by man.

It is essential, therefore, in order to prevent this disease to boil or
efficiently filter all drinking water, and to prevent the access of
mosquitoes to water. Persons infested with filariæ should sleep inside
mosquito nets, in order that they may not, when bitten by mosquitoes,
spread the disease.

=Tape-worms= are found infesting the alimentary canal of man. Each has
a double phase of existence. In the first, the characteristic head, or
_scolex_, along with a bladder-like body, lies embedded in the solid
tissues of an animal; in the second, the _strobilus_ or tape-worm,
occupies the alimentary canal of another animal. The tape-worm consists
of a number of flat segments, each of which is capable of producing
a large number of eggs, from each of which a six-hooked embryo is
developed. The segments escape from the alimentary canal, and their
ova are discharged and scattered broad-cast. These eggs are swallowed
by another animal, the hooked embryo escapes from its case, migrates
into the solid tissues, and there produces a scolex. When the host is
eaten by another animal or by man, the scolex enters the alimentary
canal, loses its bladder-like body, and developes a chain of segments.
It follows from the above that two distinct hosts are necessary to
complete the cycle of existence of these creatures, one being commonly
a herbivorous, and the other a carnivorous animal. Thus:—

       = Cystic Form.=                         =Tape-worm Form.=

  _Cysticercus Cellulosæ in  _becomes_  _Tænia Soluim in the alimentary
    the muscles of the pig_               canal of man._

  _Cysticercus Bovis in the      „      _Tænia Mediocanellata in the
    muscles of the ox_                    alimentary canal of man._

  _Cænurus Cerebralis of the     „      _Tænia Cænurus in the alimentary
    sheep’s brain_                        canal of the dog._

  _Echinococcus of man, etc._    „      _Tænia Echinococcus in the
                                          alimentary canal of the dog._

The _cysticercus cellulosæ_ has been already described (page 23). The
cystic form of the dog’s tape-worm (_echinococcus_) is a most dangerous
parasite for man. When the egg of the dog’s tape-worm is swallowed by
man, the embryo escaping from this egg burrows from the alimentary
canal, and forms large cysts, chiefly in the liver, but occasionally
in the lungs, brain, and other organs. For the removal of these,
surgical interference is required. This form of cyst is commonly known
as a _hydatid_. It is most frequently seen in Iceland and Australia,
though not uncommon in this country. Its frequency depends largely on
the number of dogs, and on the facility with which the ova of their
tape-worms can gain access to water.

The adult _Tape-worms_ are usually derived in man from eating meat
containing the cystic form. The _cysticercus_ of the pig produces
_Tænia Solium_; that of the ox, the _Tænia Mediocanellata_.

These are the two most common forms of tape-worm in man. The minute
head of _T. Solium_ has four suckers and a double row of hooklets,
28 in number; while the head of _T. Mediocanellata_ has four suckers
but no hooklets. The segments of _T. Solium_ are smaller than of _T.
Medioc._, and the structure of the segments of the two is somewhat

=Preventive Measures.=—In avoiding the various Entozoa described, it is
important (1) to _carefully avoid all underdone meat_. The eating of
smoked sausages, or of meat which is not cooked throughout, is a common
source of tape-worm and of trichinosis.

(2) _All vegetables should be thoroughly washed_: this is especially
important in the case of water-cress, lettuce, etc., which are eaten

(3) If the purity of the _water_ is not ensured, it _should be boiled_
or filtered through a Pasteur-Chamberland filter (page 98), especially
in tropical climates, and where many dogs are kept. Dogs should be kept
out of the kitchen, lest ova accidentally gain access to articles of

(4) The possibility of _flies_ and _mosquitoes_ acting as carriers of
parasitic disease must be remembered, and precautions taken.



Insects are now known to be important agents, (_a_) as carriers and
(_b_) as intermediate hosts of disease-agents.

The common =domestic fly= (_Musca domestica_) is the unwelcome
companion of man in nearly every country. The eggs are usually laid
and the larvæ undergo their development in excrement, but the female
sometimes selects meal, bread, or fruit for the purpose. In practice,
however, one of the best means of diminishing the number of domestic
flies is to insist on the daily removal of all manure, especially horse
manure, and to sprinkle the manure receptacle in the interval with
lime. The fly may obviously be the means of conveying infected material
from place to place. Anthrax has been ascribed to this cause. Nuttall
has proved experimentally that flies are able to carry the infection
of plague, and that they die of the disease. The presence of enormous
numbers of flies in cholera times has been noted. Experimentally,
flies caught in cholera wards have been found to harbour the cholera
spirillum. It is probable that they play a serious rôle in spreading
the infection of cholera. Hence all infectious dejecta (stools and
urine) should be covered until finally disposed of, and food should
be protected against flies. The same remarks apply for enteric fever.
Flies fed with pure cultures of the bacillus of enteric fever pass
these bacilli in their dejecta in a still virulent condition. In camps,
especially in connection with large armies, there is the strongest
reason for believing that flies carry infection from latrines to food.
Flies have been known to feed on the expectoration of consumptive
patients and it is possible therefore that they may thus infect food.

The =bed bug= (_Cimex lectularius_) has been stated to be capable of
conveying by its bite the infection of plague and other diseases from
an infected to a healthy person; but Nuttall’s experimental results
were entirely negative.

=Fleas= (_pulex_) probably do not play any part in spreading anthrax.
Experimentally, anthrax bacilli die off rapidly in fleas. In India,
persons who had handled rats dead of plague frequently acquired the
disease. This was explained by Simond on the supposition that the fleas
abandoned the dead rat for the human subject. The rats which appeared
to have caused plague in man were stated to have died but a short time
before; and the handling on the day after their death of rats dead of
plague was stated to be safe because the rats’ fleas had then deserted
the dead rat. It is assumed that the flea injects the poison of plague
under the skin. On the contrary it is to be remembered that the fleas
infesting rats and mice belong to a different family from that which
attacks man. Whether this is a usual means of conveying plague may
therefore be regarded as still doubtful. That rats convey plague to
man is certain; whether fleas act as an intermediary remains somewhat

The =Mosquito= family (_Culicidæ_) has been found to be an important
if not the sole means of spreading certain serious diseases to man.
To this family belong all true gnats or mosquitoes; but the only two
genera which have been proved to be able to cause disease are _Culex_
and _Anopheles_. The culex may usually be distinguished by the fact
that when alive and at rest its head is below the level of the thorax
and abdomen, thus giving the insect a hump-backed appearance, while
the body of the anopheles under the same circumstances is all in a
line.[10] The =anopheles= is more slender and its head smaller than
that of the culex. The anopheles usually confines its blood-sucking
operations to the evening and night. During the day it remains in dark
corners. It lays its eggs usually in a natural pool or pond on the
ground, on the surface of the water. In about two days a minute larva
is hatched out. This grows rapidly, assumes the pupa form, from which
the perfect insect emerges. The female insect alone is blood-sucking.
In about 20 days after birth, it lays from 150 to 200 eggs. Its
relation to malaria may be gathered from the following historical
sketch. In 1880 Laveran found in the red blood corpuscles of malarious
patients minute bodies which he regarded as not bacteria, but a very
low form of animal life, possessing amœboid movements. These grew at
the expense of the blood corpuscles, deposited a dark pigment, and
often assumed the appearance of a “rosace,” a rounded body with little
spherules at its circumference. Golgi in 1889 observed differences
between the rosaces of tertian and quartan fever, and found that the
periods of occurrences of the fever corresponded with the times of
maturation of the rosaces. It was concluded therefore, that the rosaces
caused the fever by shedding their sporules into the blood. These
sporules when thus shed were found to attach themselves to, and grow
in, other red blood corpuscles. It is now known that there are three
species of the parasite, in one of which the parasites are crescentic
in shape. The examination of a drop of blood from a patient now enables
a doctor to recognise which of these three forms of malaria he is
dealing with.

Laveran observed that certain forms of the parasite presented
“flagella,” _i.e._ filaments exhibiting very active movements. Manson
having observed that flagella were not found in blood first drawn,
but only appeared after a little time had elapsed, conceived the idea
that the function of these must be that of spores. Having previously
observed that a microscopic worm, filaria, is drawn with the blood into
the stomach of a kind of mosquito (page 278), and finds in the latter a
secondary host, he concluded that a similar cycle of events might occur
in malaria. Ross tested this theory, and by causing mosquitoes bred
in bottles from the larva to bite persons affected with the crescent
form of malaria, after repeated unsuccessful attempts, was eventually
able to find in comparatively rare mosquitoes which had thus bitten a
malarious patient, small rounded bodies embedded in the wall of the
stomach. These were watched and found to present appearances identical
with those of the parasite of malaria. Similar pigmented bodies were
subsequently found in other mosquitoes.

The malarial parasite belongs to the Protozoa, of which it is one of
the smallest members. Man is its _intermediate_ host, and the anopheles
its _definitive_ or final host. In the red blood corpuscle of man it is
a unicellar organism, from 1 µ to 8 µ in diameter. It has two methods
of reproduction, endogenous by spore formation and exogenous or sexual.
The former occurs in man; the latter in the mosquito. Without the
latter, the parasite being unable to pass from man to man, would die
with its host. In endogenous multiplication spores are formed which
separate from the original parasite and gain access to other red blood
corpuscles. The large pigmented spheres and the crescent bodies require
to enter the stomach of the anopheles to attain full development. In
the anopheles the crescents become spherical, flagella are shot out,
having a length of 4 to 5 times the diameter of a red blood corpuscle.
These represent the male element, while other spheres without flagella
are the females. By the fusion of these two a fertilised cell is
produced (_the travelling vermicule_), which now assumes the shape of
a spear-head and is actively mobile. The travelling vermicule pierces
the stomach wall of the mosquito and develops into a _zygote_. If
an infected mosquito is examined on a succession of days under the
microscope, the following stages can be traced. The zygote consists of
pigmented spheres 7 to 8 µ in diameter, lying in the muscular fibres
of the mosquito. These grow, and become surrounded by a capsule.
Smaller spheres form and subdivide, bud-like processes develop on
their surfaces; these gradually become sickle-shaped and protrude into
the body cavity. They increase in size. until they attain dimensions
of from 40, to 60 µ. Eventually they rupture, and the sickle-shaped
bodies (_sporozooites_) escape and are carried in the body fluid of
the mosquito to its salivary glands. These sporozooites are about 14 µ
long, and human infection is caused by them. They have been traced as
far as the end of the proboscis of the mosquito. (See also page 307).



The prevention of disease depends largely on a knowledge of its
causes. Disease may be due to a personal life not in accordance with
physiological laws; or to some cause or causes acting _ab extra_. With
advance of knowledge the number of diseases which can be proved to
be caused by a _contagium vivum_ introduced from without is steadily
increasing. We have already discussed the influence of habits, of
clothing, exercise, sleep, and food on health, and have shown how
errors in these respects may lead to disease. It now remains to
consider more particularly the prevention of diseases, due to the
introduction into the system of contagia.

In the study of such diseases three chief factors require
consideration: (1) the contagium itself; (2) conditions of environment,
as climate, soil, season, weather, etc., which may favour or impede
its spread; and (3) personal conditions which similarly influence it.
Of these age, heredity, fatigue, injury, diet, and race are specially

The first two groups of diseases given in the Registrar-General’s
classification of causes of death are (1) Specific Febrile or Zymotic
Diseases, and (2) Parasitic Diseases. The objection to the word
“specific” is that, although in most instances diseases in this group
are “specific” in the sense that they are caused by a particular
microbe, _e.g._ tetanus, anthrax, tuberculosis, in a few instances the
same lesions may be caused by several microbes, _e.g._ septicaemia
(blood-poisoning), pneumonia. “Zymotic” was the name given by Farr,
in view of the analogy of the febrile process to that of alcoholic
fermentation. In both there is the introduction of a living germ
or germs; in both a period of “incubation” in which nothing can be
observed; then follows the active disturbance; and in the disease, as
well as in the fermenting liquid, the process is stopped, when the
microbes have multiplied to a certain extent, a temporary or permanent
protection being the result. The best name for the diseases in this
group is “Infective.” Parasitic diseases, like ringworm, scabies, or
trichinosis, are also infective; but for convenience may be described
separately as “parasitic.”

The relation between the words “infectious” and “contagious” requires
explanation. A disease like measles or small-pox, which can be
transmitted from person to person, without immediate contact between
the two, is termed =infectious=. In these cases the infection is
conveyed by mucus expectorated or by dust blown about, or carried in
apparel, etc., from the first patient. Such diseases may also, of
course, be communicated by direct contact. If direct contact between
the sick and well is indispensable for the transmission of a disease
it is called =contagious=. There is no such hard line in nature,
although some diseases can be more easily communicated than others.
The term contagious is usually applied to parasitic diseases like
ringworm and scabies, but even these can be communicated by means of
infected articles as well as persons. The word contagious should be
abandoned for all the acute febrile diseases. The word =infective= is
used to include all specific febrile diseases, however spread. This
word, therefore, includes not only infectious and contagious diseases,
but also diseases spread by =inoculation=, _i.e._ injection of the
infection under the skin. Thus malaria is not infectious from patient
to patient; but can be inoculated by the mosquito.

=Infective Diseases= are either acute or chronic. Of _acute_ infective
diseases small-pox and enteric fever are typical examples; of
_chronic_, tuberculosis and syphilis.

It was formerly supposed that in certain diseases the contagium or
infective agent grew in external noxious matter, a _miasm_ being
produced; while in other diseases _contagion_ was only produced
direct from patient to patient; and others originated in either way.
Hence the classification of infective diseases into (_a_) miasmatic,
(_b_) contagious, and (_c_) miasmatico-contagious diseases. This
classification has now been abandoned. Thus influenza and ague were
formerly thought to be miasmatic; but the former is spread by personal
infection; the latter by inoculation of the contagium by an infected

=Bacteriology= has thrown an immense light on the causation of
infective diseases. A large number of these have been proved to be
caused by bacteria, and by analogy we infer the same thing for many
others. =Koch= has laid down the following =postulates= as necessary
before it can be stated that a particular disease is directly caused by
a given microbe:—

 (1) The microbe shall be demonstrated in the diseased tissues or blood
 of man or an animal suffering or dead from the disease.

 (2) The microbes shall be isolated from these and cultivated in
 suitable media until obtained in pure culture. That is to say,
 matter containing the microbe, taken from the infected source, must
 be cultivated in artificial media outside the animal body, under
 conditions excluding the possibility of the introduction of other
 microbes, until pure cultures of these microbes are obtained, and
 these microbes must be transplanted from generation to generation,
 until it is certain that no trace of non-living matter derived from
 the original animal body remains in the culture.

 (3) A pure culture of the microbe, thus obtained, shall, when
 introduced into the body of a healthy susceptible animal, reproduce
 the disease in question.

 (4) The microbe in question shall be found in the animal so affected.
 Kanthack adds a further condition, that

 (5) The toxins and poisonous substances obtained from the artificial
 cultivations shall agree chemically and physiologically with those
 obtained from the diseased animal.

All the preceding conditions have been fulfilled for anthrax,
diphtheria, and tetanus; and the first four conditions have been
fulfilled in regard to tuberculosis, glanders, gonorrhœa, malignant
œdema, and actinomycosis. In enteric fever and influenza the first two
conditions have been met; but inoculation experiments (3) have failed.
In leprosy and relapsing fever the first condition is met, but (2) has

In the following diseases the specific microbe has not been isolated,
though from analogy it is believed that each of them is caused by such
a microbe:—

  Rubella (German measles).
  Typhus fever.
  Scarlet fever.
  Varicella (chicken pox).
  Variola (small-pox).
  Whooping Cough.
  Hydrophobia, etc.

Erysipelas occupies a special position. It is a specific disease due
to a microbe, which, when it attacks other parts than the skin, may
produce abscesses, boils, or blood-poisoning.

Bacteria are either =saprophytes=, _i.e._ they can grow on dead organic
or even inorganic matter; or =parasites=, _i.e._ they are dependent
for their existence on a living plant or animal which they invade.
There are two varieties of each of these, obligate and facultative.
An _obligate parasite_ can develop only within a living host; while a
_facultative parasite_ can, according to circumstances, lead either
a parasitic or saprophytic form of existence. The fact that certain
contagia are completely, and others only partially, parasitic brings
out important differences in their life-history. Thus, so far as we
know, the contagia of scarlet fever, measles, small-pox and hydrophobia
do not multiply outside the body. Hence there is a reasonable prospect
of annihilating them by measures of disinfection and isolation. The
position of diphtheria is doubtful. It may have a saprophytic phase of
life. The contagium of tuberculosis, as well as of erysipelas, may have
a life outside the host, though to what extent is doubtful. Cholera and
enteric fever, although generally communicated by infection, appear
sometimes to be communicated by contagia grown in saprophytic life,
remote from preceding cases.

The infection caused by bacteria may be _local_ or _general_. Thus in
tetanus and in diphtheria the invading bacteria usually remain at their
original point of invasion (under the skin in tetanus, in the throat
in diphtheria). In anthrax always, and often in enteric fever, they
are present in the general circulation. In both instances the symptoms
of disease are due chiefly to the toxic products or =toxins= formed
by the bacteria. These toxins are enzymes, ptomaines, tox-albumins,
etc. The specific toxins of anthrax, diphtheria, and tetanus have been
identified; and by this means the possibility of neutralising them is

The =channels of infection=, _i.e._ of invasion of contagia, are the
skin and the mucous membranes, particularly of the digestive and
respiratory tracts.

The =Incubation Period= of an infectious disease is the interval
elapsing between the receipt of infection and the earliest development
of symptoms. The _period of incubation_ of the chief infectious
diseases is shown in the following table:—

  │                  │    ON THE       │  ANY PERIOD BETWEEN    │
  │_Scarlet fever_   │       4th day.  │    1 and  7 days.      │
  │                  │                 │                        │
  │_Diphtheria_      │       2nd  „    │    2  „   5  „         │
  │                  │                 │                        │
  │_Small-pox_       │      12th  „    │    1  „  14  „         │
  │                  │                 │                        │
  │_Chicken pox_     │      14th  „    │   10  „  18  „         │
  │                  │                 │                        │
  │_Typhus fever_    │      12th  „    │    1  „  21  „         │
  │                  │                 │                        │
  │_Enteric fever_   │ 14th-21st  „    │    1  „  28  „         │
  │                  │                 │                        │
  │_Cholera_         │  1st-3rd   „    │A few hours and 10 days.│
  │                  │                 │                        │
  │_Measles_         │ 12th-14th  „    │   10 and 14 days.      │
  │                  │                 │                        │
  │_Rötheln_         │                 │                        │
  │(_German measles_)│      14th  „    │   12  „  18  „         │
  │                  │                 │                        │
  │_Mumps_           │      19th  „    │   16  „  24  „         │
  │                  │                 │                        │
  │_Whooping cough_  │      14th  „    │    7  „  14  „         │
  │                  │                 │                        │
  │_Influenza_       │       2nd  „    │    2  „   6  „         │

The period of incubation is several weeks in hydrophobia and syphilis,
and may be several years in leprosy.

Following the period of incubation, come the premonitory symptoms,
which usually are somewhat sudden in onset. For the chief =symptoms of
onset= see page 318.

Persons vary in susceptibility to attack by different infective
diseases. The intensity of an attack depends on the condition of the
patient, and on the number and the virulence of the particular microbes
infecting the patient. In certain families attacks of particular
diseases are more severe, and attacks are more liable to occur than in

It has been shown in certain diseases that the cells and the fluids of
the body have a protective effect against infection. This protective
action varies in different persons, and in the same person at different
times. The cells of the body (_phagocytes_) swallow up and destroy a
certain number of bacteria. This action is called =phagocytosis=. It is
overcome when the dose of contagium is excessive, or when the vitality
of the individual is lowered, especially the local vitality at the part
attacked. Thus children with “weak throats” are particularly prone to
scarlet fever and diphtheria.

The =protection= afforded by =one attack= of an infective disease
against its recurrence varies greatly. A second attack of small-pox is
very rare, of scarlet fever less uncommon, of diphtheria common. In
erysipelas, influenza, pneumonia, and rheumatic fever, second or even
more numerous attacks are common.

=Immunity= against an infective disease may be _natural_, but is more
often _acquired_ by an attack of the disease in question. This latter
_immunity_ is _active_, and is due to the formation in the tissues of
the immunised person or animal of substances produced by the reaction
of these tissues to the stimulus of the contagium. Thus a pig when
it has recovered from an attack of swine-plague has produced what
are called in German _antikörpers_, and its tissues are now a medium
unfavourable to the growth of the bacillus of swine-plague. If the
serum of the protected pig is injected under the skin of another pig,
the latter acquires _passive immunity_ against swine-plague, which is
not so persistent as active immunity.

=Active Immunity= can be produced (1) by an attack of an infective
disease, or (2) by artificial inoculation (under the skin) of the
contagium of the disease, producing a milder attack of the disease.
This may be done (_a_) by inoculating _small doses of a virulent
contagium_, as in the inoculation of small-pox from a previous patient;
or (_b_) by inoculating an _attenuated virus_, as in vaccination.
Inoculation of small-pox virus usually produced a milder attack than
infection by ordinary means; but patients thus inoculated were a
great source of danger to other persons. In vaccination the virus
of small-pox is employed, which has become attenuated by passing
through the calf. In its passage, it has lost the power of producing
anything beyond a vesicle at the point of inoculation. The principle
of protecting by attenuated virus was extended by Pasteur, who was
able to render animals resistant against anthrax, swine-fever, and
quarter-evil, and hens against fowl-cholera, by inoculating them with
attenuated cultures of the contagia of these diseases. Haffkine has
applied the same method on a large scale for cholera.

The above are methods of bacterial vaccination. Salmon and Smith
have shown that artificial active immunity can be produced also by
(3) _toxin-injection_. They artificially cultivated the hog-cholera
bacillus in broth. This broth was then sterilized, the bacilli being
killed, but their products remaining. By injecting pigeons with this
sterilized broth they made them resistant to subsequent infection by
the bacillus itself, thus proving that immunity can be produced by
chemical as well as by biological means. The immunity was proportional
to the dose of the toxin absorbed. By gradually increasing the dose,
it was found practicable to confer immunity, not only against doses of
toxin that would otherwise have been fatal, but also against bacterial
infection by the particular bacillus used in manufacturing the toxin.

=Passive Immunity.=—Behring and Kitasato found that if the toxin (free
from the bacilli) of tetanus be injected into an animal in increasing
doses until it becomes immune against infection by the bacilli of
tetanus, the blood serum of the animal in question injected into white
mice confers the same immunity on them. The protection thus conferred
is only temporary. Exactly the same procedure has been adopted for
diphtheria, and it is now found that by injecting _anti-diphtheritic
serum_ into children who are exposed to the infection of diphtheria,
they can for several weeks be prevented from developing the disease.
This is of great practical importance, as meanwhile the source of
infection can have been removed. Furthermore, the _protective serum is
also curative_, and by its means diphtheria, if early treated, can be
reduced from a dangerous to an insignificant disease.

Various =theories= have been propounded =to explain immunity=. Pasteur
supposed that the special pabulum or food of the bacillus of the given
disease became exhausted; but this does not fit in with the immunity
that can be produced by toxins and anti-toxins. Chauveau supposed
that certain bacterial products are retained in the body, rendering
it unsuitable for further growth of the particular bacillus; just as
more than 14 per cent. of alcohol in a saccharine solution prevents
further fermentation. This does not explain all the facts. Metschnikoff
concluded that the fight of the leucocytes and phagocytes of the body
against weaker bacilli, gave the power of fighting and overcoming a
more virulent bacilli, and that these properties of the cells were
transmitted to later generations of body cells. This theory fails
to explain the acquired immunity against toxins as well as against
bacteria which occurs. The discovery that the blood and other normal
tissue fluids possess some power of destroying bacilli has relegated
the phagocytal theory to a secondary position.

=Natural Immunity= varies in different animals. Thus enteric fever,
scarlet fever, and measles are not known to occur except in man.
Tuberculosis, anthrax, hydrophobia (called rabies in the dog), glanders
and tetanus are common to man and certain other animals. Man, cattle
and pigs frequently suffer from tuberculosis; goats, sheep, horses, and
dogs are practically immune to it.

=Epidemic and Endemic Diseases.=—Infective diseases may occur
_sporadically_, in _epidemics_, or in _pandemics_, _i.e._ epidemics
spread over a number of countries. The word =epidemic= is used here to
mean specially prevalent, and not to apply only to infective diseases.
Thus there may be an epidemic of arsenical poisoning from contaminated

Certain infective diseases are =endemic= or topical, _i.e._ they have
special homes or centres, from which they occasionally spread as
epidemics. Yellow fever, cholera, and malaria belong to this group. In
a minor degree enteric fever, epidemic diarrhœa, and tuberculosis may
be described as endemic.

Each infective disease has a special =seasonal incidence=. Of these the
most important are the _autumnal_ group, viz.

  Epidemic Diarrhœa, maximum prevalence in July and August.
  Enteric Fever         „        „      „  November, but excessive,
                                            Aug. to Dec.
  Erysipelas            „        „      „  Nov. to Dec.
  Diphtheria            „        „      „  Nov. and Dec., excessive,
                                            Sept. to Dec.
  Scarlet Fever         „        „      „  Oct., excessive in Aug.
                                            to Dec.

Of other infective diseases

  Small-pox has its maximum prevalence in May, but is excessive Jan.
                                           to June.
  Whooping Cough      „         „      „  Dec. to May.

Measles commonly has two seasonal maxima, in June and December with
intervening minima.

=Causes of Epidemics.=—Measles recurs in the large towns of England
every alternate year. Other infective diseases occur at less regular
intervals. The recurrence of epidemics is not solely due to personal
infection and the accumulation of a population at susceptible ages.
There are longer =cycles= of the causes of which but little is known.
Thus scarlet fever has been shown by Longstaff and Gresswell to become
epidemic chiefly in dry years; and I have shown that diphtheria and
rheumatic fever become widely epidemic under the same conditions,
diphtheria becoming so only when a series of dry years occur in
immediate succession.



Acute Infectious Diseases are characterised by certain definite

1.—_They are usually infectious or contagious._ It is preferable to use
these two terms as interchangeable. The modes in which infection is
received vary greatly with different fevers.

(1) Some can only be propagated by _inoculation_—the introduction
through an abraded surface of a minute quantity of the poison; as in
glanders and hydrophobia. Others, again, _may_ be introduced in this
way, but are usually acquired in another manner, as scarlet fever,

(2) Some are carried through the _atmosphere_. The contagium of
small-pox can be carried as far as any, while that of typhus fever only
traverses a few feet. The atmosphere acts as a conveyer of infection,
and the infectious matter must necessarily, in most instances, be in
the condition of dust to enable it to be wafted by currents of air or
disturbed by the movements of persons in an infected room.

(3) _Clothes_, books, and furniture are not uncommonly carriers of
infection. An old letter, or a lock of hair, has even after many years’
concealment in an enclosed space produced infection on being brought to
light. Woollen articles convey infection more easily than calico, and
dark clothes better than light coloured. A fever nurse’s clothes should
never be woollen, but some washable material.

(4) _Drinking water and food_ often form a vehicle for infection. Milk
and water are the two usual sources of infection; but uncooked food,
especially oysters and mussels, fed in sewage-polluted estuaries,
may produce the same effect. Cholera, enteric fever, dysentery, and
summer diarrhœa are the chief diseases from this source; but scarlet
fever and diphtheria occasionally have a similar origin. Milk may be
infected from having been handed by an infectious patient; or it may
possibly convey infection of the disease from which the cow at the time
is suffering, _e.g._, tuberculosis (see also page 312). Water may be
contaminated with sewage or the excreta of a single infectious patient.

2. _They retain their specific character and origin._ Small-pox never
produces scarlet fever, nor _vice versâ_; and it is found universally
that all the specific fevers “breed true,” each one retaining its
identity. More than this, a previous case of the same fever can nearly
always be detected on careful examination. Overcrowding and other
insanitary conditions diminish the resistance to infection, and may
increase its virulence.

3. _The behaviour of contagia_, when received into the system, is
characteristic of these diseases. There is first of all a period of
latency or _incubation_, during which no symptoms are manifested (see
page 287.) The incubation period is followed by the characteristic
symptoms of the particular fever, which disappear in a variable period,
leaving the patient, as a rule, more or less _insusceptible to a second
attack_ (see page 288).

Throughout the progress of the disease, except in the period of
incubation, the patient is able to communicate his disease to persons
about him who have not been rendered safe by a previous attack. The way
in which he thus communicates his disease varies in different cases. In
scarlet fever, the throat and skin are the chief sources of contagion;
in influenza, whooping-cough, and measles, the secretions from the
respiratory passages; in hydrophobia, the saliva; in enteric fever and
cholera, the vomit and stools.

=Prevention of the Spread of the Chief Acute Infectious Diseases.=—We
may divide these into three classes. (1) Those which are infectious by
contact with the patient or by the atmosphere around him. (2) Those in
which the intestinal and renal evacuations are almost alone infectious;
as enteric fever and cholera. (3) Those in which inoculation through
an abraded surface is generally if not always necessary to produce


The contagium of small-pox is very tenacious of life. All parts of the
body, and all secretions and excretions contain it. As in typhus it
adheres to every article in the room, but unlike typhus is possessed
of great vitality, and if not exposed to the air may be active after
many years. There is considerable evidence indicating that the
contagion of small-pox may occasionally be _conveyed aerially_ for a
considerable distance, for even a quarter or half a mile from hospitals
in which small-pox patients are isolated. Whether this is the aerial
convection of infection, or in part at least due to carelessness of
persons connected with the hospital in their movements to and fro,
may remain an open question; but such hospitals in the midst of towns
are in practice a mistake; and in London small-pox has been found to
be more manageable since its small-pox patients were all conveyed to
extra-urban hospitals. The means for the prevention of small-pox are
(1) Isolation of infectious patients. (2) Disinfection of all infected
articles. For particulars under these two heads, see pages 319 and 324.
They must be carried out most rigidly in this disease. (3) Vaccination
and re-vaccination.

=Inoculation of small-pox= virus was largely practised as a means of
ensuring a comparatively mild attack, until it was made illegal in
1840. Sometimes, however, the attack thus produced was fatal, and every
case of inoculated small-pox became a new focus of infection, and a
source of high mortality, especially among young children.

=Vaccination.= About the year 1795 Dr. Edward Jenner was informed by
a milk-maid that she could not take small-pox, as she had already
contracted the natural cow-pox during milking. Many had previously
heard this same statement made; but Jenner was the first to put the
matter to the test. He took the lymph or virus from a woman who had
accidentally acquired cow-pox (vaccinia) from a cow, and inoculated
a boy with it. Some months later he inoculated the same boy with
small-pox, and a second time five years afterwards, without producing
small-pox on either occasion. Many other experiments were made, all
confirming these results; and in 1798 Jenner published his results.

The practice of vaccination gradually became more general, and was
followed by a progressive decrease in the mortality from small-pox.

Cow-pox or vaccinia is small-pox modified and mitigated by its
passage through the system of the cow, and not a spontaneous disease
of the cow. By its passage through the cow it has become attenuated
and altered. Instead of a general eruption all over the body, there
are vesicles only at the point of inoculation; and vaccinia, unlike
small-pox, is not communicable from person to person except by
inoculation. Furthermore it is in the vast majority of instances an
extremely mild ailment, not involving more than a few days discomfort.

Objection is taken to vaccination for small-pox on the ground that
serious diseases such as syphilis, erysipelas, and tuberculosis may be
inoculated at the same time. With lymph obtained from healthy children
this is impossible. Most of the cases of infection described have been
in reality hereditary disease, the local irritation of vaccination
serving to call into activity the morbid tendencies of the child. The
risk of such infection is infinitesimal; it may be reduced to zero by
moderate care and attention to detail. With modern antiseptic methods,
it is very rare for a vaccination sore to “go wrong.” Erysipelas may be
inoculated from dirt getting into a vaccination sore, as it may be into
any other sore; but with cleanliness this need not occur; and in fact
very seldom does occur. The risks are so small as to be negligible;
and if the protection afforded is one tithe of what is claimed for
it, no parent is justified in withholding this protection from his
infant. The _law as to vaccination_ requires that every infant shall be
vaccinated within six months of its birth, domiciliary visits for this
purpose being made by the public vaccinator. The obligation can only
be avoided by a statement on oath before a magistrate by the parent of
conscientious objection to vaccination.

=Does Vaccination protect against Small-Pox?= The registration of
deaths for the whole country only began in 1837, and before this
period death-rates from small-pox in terms of the population cannot
be accurately stated. Since that time there has been less or more
vaccination, so that it is difficult to obtain a true comparison
between periods with and without vaccination. Some indication of
the facts in London prior to 1801, when the first English census was
taken, may be obtained from the fact that in 1796 (two years before
the date of Jenner’s “Inquiry,”) small-pox reached its highest point,
causing 18½ deaths out of every 100 total deaths from all causes.
In the præ-vaccination period small-pox was 9 times as fatal as
measles, and 7½ times as fatal as whooping-cough (McVail), while
since vaccination has been practised it has sunk to an insignificant
position, when compared with these diseases. Dr. Guy found that in
London there were in 48 years of the seventeenth century ten epidemics,
in the whole of the eighteenth century 19 epidemics, and in the
nineteenth century no epidemic during which the deaths from small-pox
caused one-tenth or more than one-tenth of the total deaths from all
causes in any year. The worst year under obligatory vaccination in
London was 1871, in which barely 4½ per cent. of the total deaths
was due to small-pox, a proportion which was exceeded in the eighteenth
century ninety-three times.

In Sweden, the highest death-rate _before vaccination_ (1774-1800)
was 7·23 per 1,000 inhabitants, the lowest 0·31; under _permissive
vaccination_ (1801-1815) the highest 2·57 per 1,000 inhabitants, the
lowest 0·12; under _compulsory vaccination_ (1816-85) the highest 0·94
per 1,000 inhabitants, the lowest 0·0005. It has been stated that these
results, which might be extended by quotations from the statistics
of other countries, have been obtained not by vaccination, but by
improved sanitation, including in this term not only improved housing
and better water and food supply but also increased means of isolating
the infectious sick. Improved housing may by diminishing overcrowding
aid in diminishing the spread of this disease. Whether in view of the
immense increase in the proportion of the population which lives in
towns, it can be said that this has occurred is doubtful. Hospital
isolation undoubtedly prevents the spread of infection when promptly
effected. But a large share of the improvement in small-pox mortality
occurred before either hospital or home-isolation of small-pox patients
was generally enforced. There is no reason for supposing that impure
water or food, or nuisances about houses have any connection with the
origin or spread of small-pox, any more than they have with the origin
or spread of measles or whooping-cough; which still remain as prevalent
as in the past. Further light can be thrown on the subject by an
examination of the age-incidence of small-pox, and of its attack-rate
and severity in vaccinated and unvaccinated respectively.

The =age incidence of deaths from small-pox= has, since 1847, when
returns classified according to age became available, undergone a
remarkable alteration. Prior to 1870 the small-pox deaths in infants
nearly always formed 20 per cent. or more of the total mortality from
this disease, between 1870 and 1890 they did not greatly exceed 10 per
cent. of the total, while since 1890 they have again begun to form an
increasing proportion of the total small-pox mortality. At ages 1-5 the
change is even more remarkable. Before 1870 deaths at these ages nearly
always exceeded 30 per cent. of the total; since 1870 they have varied
between 5 and 14 per cent. of the total; and since 1890 they have,
like the proportion of deaths under one, again increased. At the higher
ages the proportion of deaths has correspondingly increased, so that
the curves of age incidence have become curiously inverted.

The lowered birth-rate can only account for a small portion of this
transference of the chief mortality due to small-pox from childhood to
adult life.

Furthermore it must not be supposed that the only change which has
occurred is that the deaths which formerly occurred in childhood now
occur in adult life. The death-rate at all ages has greatly declined.
The only explanation which in my judgment satisfactorily explains
this remarkable change in age-incidence of small-pox mortality is
the fact that vaccination protects children from small-pox and that
the protection diminishes, though it never entirely disappears, with
advancing years. This conclusion is confirmed by the evidence obtained
as to the proportion of vaccinated and unvaccinated attacked, and as to
the severity of the attacks occurring when a community is invaded by

=Attack-rate among Vaccinated.=—If the protective effect of
vaccination, like that of a preceding attack of small-pox, wears off,
it will not be expected that no attacks of small-pox will occur among
the vaccinated. For evidence of immunity from attacks we must examine
the records as to =revaccinated= persons exposed to infection. During
the six years 1890-95, out of a staff in the London small-pox hospitals
varying from 64 to 320, the percentage attacked by small-pox was _nil_,
except in 1892 when it was 1·4, and in 1893 when it was 1·9.

Taking the experience of towns in which during recent years epidemics
of small-pox have occurred, the following attack-rates have occurred.
By attack-rate is meant the percentage number of attacks occurring
among persons living in infected houses. By fatality is meant the
number dying out of 100 attacked.

  │            │    ATTACK RATE UNDER      │   ATTACK RATE OVER       │
  │            │     10 YEARS OF AGE.      │    10 YEARS OF AGE.      │
  │            ├───────────┬───────────────┼───────────┬──────────────┤
  │_Dewsbury_  │   10·2    │     50·8      │   27·7    │     53·4     │
  │_Leicester_ │    2·5    │     35·3      │   22·2    │     47·6     │
  │_Gloucester_│    8·8    │     46·3      │   32·2    │     50·0     │

=Severity (Fatality) among Vaccinated.=—The experience of the same
three towns comes out as follows:—

  │            │    ATTACK RATE UNDER      │   ATTACK RATE OVER       │
  │            │     10 YEARS OF AGE.      │    10 YEARS OF AGE.      │
  │            ├───────────┬───────────────┼───────────┬──────────────┤
  │_Dewsbury_  │    2·2    │     32·1      │    2.6    │     18·7     │
  │_Leicester_ │    0.0    │     14·0      │    1.0    │      7·8     │
  │_Gloucester_│    3·8    │     41·0      │   10·0    │     39·7     │

In view of such results as the above it is not surprising that the
Royal Commission, in their majority report, summed up the advantages of
vaccination as follows:

 “(1) That it diminishes the liability to be attacked by the disease.

 “(2) That it modifies the character of the disease, and renders it
 (_a_) less fatal, and (_b_) of a milder or less severe type.

 “(3) That the protection it affords against attacks of the disease
 is greatest during the years immediately succeeding the operation of
 vaccination. It is impossible to fix with precision the length of this
 period of highest protection. Though not in all cases the same, if a
 period is to be fixed, it might, we think, fairly be said to cover in
 general a period of nine or ten years.

 “(4) That after the lapse of the period of highest protective
 potency, the efficacy of vaccination to protect against attack
 rapidly diminishes, but that it is still considerable in the next
 quinquennium, and possibly never altogether ceases.

 “(5) That its power to modify the character of the disease is also
 greatest in the period in which its power to protect from attack is
 greatest, but that its power thus to modify the disease does not
 diminish as rapidly as its protective influence against attacks, and
 its efficacy during the later periods of life to modify the disease is
 still very considerable.

 “(6) That re-vaccination restores the protection which lapse of time
 has diminished, but the evidence shows that this protection again
 diminishes, and that, to ensure the highest degree of protection which
 vaccination can give, the operation should be at intervals repeated.

 “(7) That the beneficial effects of vaccination are most experienced
 by those in whose case it has been most thorough. We think it may
 fairly be concluded that where the vaccine matter is inserted in three
 or four places, it is more effectual than when introduced into one or
 two places only—and that if the vaccination marks are of an area of
 half a square inch, they indicate a better state of protection than if
 their area be at all considerably below this.”


Scarlet Fever and Scarlatina are the same disease. It is extremely
infectious, the contagium retaining its virulence for protracted
periods. It occurs in epidemics at irregular intervals. During recent
years the type of scarlet fever has become greatly attenuated, and
this constitutes one of the difficulties of prevention, as the mild
form of the disease is apt to be overlooked. The _fatality_ per 100
persons attacked varies greatly with age. It is highest in children
under four, rapidly declining with increasing age. Hence the importance
of protecting children from attack in early life. Two results follow
from the wise precautions taken to prevent attack early in life. (_a_)
With each successive year of life the liability to attack, when exposed
to infection, diminishes; (_b_) the danger of the attack if it occurs
and its liability to be fatal becomes rapidly less with greater age.
The most common _mode of infection_ is by contact with a previous
patient. Outbreaks due to milk infected by a scarlatinal patient
also occur. Infected cream has also been known to convey infection.
In a milk outbreak the patients would be found chiefly among the
customers of a special dairyman, the cases occur almost simultaneously,
except secondary cases which may be infected from the first. The
_simultaneous_ occurrence of two or more attacks in one house,
especially if the same thing happens in a number of houses should throw
suspicion on the milk supply. It has been suggested that scarlet fever
may originate apart from human infection, from a special disease of the
cow, but the evidence on this point is inconclusive.

The _duration of infection_ is usually reckoned until the desquamation
of the skin is complete, _i.e._ about six or seven weeks from the
onset of the attack. Occasionally it is more protracted even though
desquamation is complete, infection appearing to persist in discharges
from the nose and ear and in sore places inside the nostril and
possibly in other parts. The period of greatest infectivity is in the
earlier part of the disease, when the throat is inflamed. The common
notion that the disease is most infectious during the later period,
that of desquamation, is erroneous. The micro-organism causing scarlet
fever has not certainly been identified. The measures of prevention are
those common to infectious diseases (page 317).


Measles is an extremely infectious disease, before as well as after the
rash appears on the fourth day of the disease. The infectivity of the
catarrhal stage constitutes one of the main difficulties in preventing
its spread, as measles may be unrecognisable at this stage. The common
notion that measles and whooping-cough are comparatively harmless
infantile complaints will be dissipated by a study of the comparative
death-rate for the five years 1891-5 per million persons living in
England and Wales:—


  _Small-pox_        20
  _Measles_         408
  _Scarlet fever_   183
  _Typhus fever_      4
  _Enteric fever_   174
  _Whooping-cough_  398
  _Diphtheria_      253
  _Diarrhœa_        630

It is a mistake also to suppose that measles and whooping-cough are
only serious when neglected. Such neglect greatly increases the
likelihood of death from bronchitis or pneumonia; but the diseases
themselves, especially measles, are frequently fatal during the acute
early stage. More children are attacked with measles under the age
of five than at any other age, and the greatest number between two
and four years of age. The greatest fatality is in the second year
of life, when it may be 24 per cent. of those attacked, as compared
with between two and three per cent. in the fourth year of life, and
a trifling amount at higher ages. These facts explain the folly of
allowing children to have an infectious complaint when another child in
the house is attacked, “to have it over at one trouble.” Such action
is pregnant with evil results. (1st) Severe cases occur, in which a
fatal result ensues; and even where death does not occur, the child
may be left weakly and very prone to become tuberculous. (2nd) Every
additional case forms a new centre of infection. It is like the old
practice of inoculation for small-pox; the individual is protected, but
becomes a source of danger to all around him. If there is only one
case of measles in a family the risk to neighbouring households is much
smaller than where several children are infected. (3rd) Every year that
a child’s attack can be delayed, increases his chance of recovery if he
is subsequently attacked, and diminishes the likelihood of his being

The _duration of infection_ should be reckoned as at least three weeks.
The contagium of measles does not appear to hang about rooms with the
persistence of that of scarlet fever, and less stringent disinfection
is required.


Very few people have reached adult life without having suffered
from this disease, as well as measles. This is chiefly due to
the carelessness in mixing infected with healthy children. One
frequently hears the peculiar and characteristic cough of a child
with whooping-cough, in public assemblies, in railway trains, or in
the out-patient rooms of hospitals. The contagium of whooping-cough
is conveyed chiefly by the expectoration, which becoming dry, may be
scattered like that of phthisis, as dust. Clothing conveys infection
easily; visits to infected children should, therefore, be prohibited to
all who have to mix with susceptible children.

The _duration of infection_ should be reckoned as at least six weeks
from the first recognisable symptoms. It may be longer than this.


This disease has become increasingly prevalent in the last ten years
after a period of only slight prevalence for about twenty-five years.
I have shown that epidemics of diphtheria occur during a succession of
years of protracted drought. Diphtheria is more common in girls than
boys, possibly owing to their more affectionate habits; and occurs
chiefly under ten years of age, the fifth year of life being that of
greatest prevalence. Unlike the acute infections hitherto considered,
the bacillus causing diphtheria has been identified and cultivated
in the laboratory (called the Klebs-Loeffler bacillus or diphtheria
bacillus). Direct infection from patient to patient is probably more
common than indirect infection by clothes, etc., though the latter
occurs. The infection may hang persistently about a house and its
belongings, in the absence of complete purification. When diphtheria
is prevalent slighter sore throats occur, sometimes before true
diphtheria is detected. This led to the theory that under conditions
of overcrowding, especially in schools, there occurred in the
micro-organisms causing these sore-throats “the progressive development
of the property of infectiveness.” Possibly these were slight
non-typical attacks of diphtheria. Such attacks occur also during
epidemics of diphtheria, and unless specimens (“throat swabs”) from
these sore-throats are examined bacteriologically, are likely to spread
diphtheria by attendance at school, etc. Aggregation in schools seems
to intensify the contagium of diphtheria. The practices of kissing, of
transferring sweetmeats from mouth to mouth, of cleaning slates with
saliva, are common means of spreading it. Effluvia from foul drains
and sewers have been commonly held to cause diphtheria. If they aid
in producing it, it is rather by lowering the vitality and causing
ordinary sore throat. Sore throats and catarrhs make the subjects of
them much more prone to diphtheria (see also page 117). Damp houses
have been stated to favour the development of diphtheria. Probably
they do so in the same way as effluvia from drains. It is likely that
the diphtheria bacillus has a saprophytic stage of existence in the
soil, as indicated by its excessive prevalence in dry warm years.
Besides direct infection from patient to patient and indirect infection
by _fomites_ (_i.e._ in clothing, etc.), milk occasionally causes
epidemics of diphtheria. The infection has been usually caused by the
handling of the milk by an infectious person. In certain outbreaks no
human contamination of the milk could be discovered; and it has been
surmised that an analogous disease in the cow may cause diphtheria in
man. This is still a moot point. Fowls, cats, and other animals are the
occasional victims of diphtheria, and may convey it to man.

The _duration of infection_ in diphtheria is usually less than six
weeks; but it may be much more protracted. In some instances long after
all naked-eye evidences of diphtheria has disappeared, bacteriological
examination may still show the presence of the diphtheria bacillus for
two or three months; in rare cases even longer. The protection afforded
by one attack of diphtheria against a second is slight and only
temporary. The _means of prevention_ are isolation and disinfection as
for other infectious diseases. Two additional means are available (_a_)
_bacteriological diagnosis_; (_b_) prophylactic injection of antitoxic
serum. Many sore throats without membrane on the throat are due to the
diphtheria bacillus. Even if membrane be present there may be doubt
as to whether the case is true diphtheria. Hence the importance of
bacteriological examination.

 The patient’s throat is swabbed with cotton-wool which has been
 rolled around a metal probe and sterilised. The wool is then smeared
 over sterilised and solified blood serum in a test tube. It is then
 incubated over night at a temperature of 37° C. Next morning the
 minute growth that has occurred on the surface of the blood serum
 is spread on a microscopic cover-glass, appropriately stained, and
 examined microscopically. If diphtheria bacilli are present, they can
 be recognised by their form and arrangement. The same means enable us
 to ascertain when a patient has recovered, whether he is fit to be
 released from isolation.

_Antitoxic serum_ has been found to be a valuable prophylactic and
curative agent.

 The serum is obtained as follows: Sterilised broth is inoculated with
 virulent diphtheria bacilli, and grown at 37° C. for a week or more.
 The broth is then filtered through a Pasteur filter. The filtrate
 contains _toxine_ free from bacilli. Some of this toxine is injected
 under the skin of a horse. A few days later the dose is repeated,
 gradually increasing amounts being injected until injection of further
 quantities of the toxine is found experimentally not to increase
 the antitoxic value of the horse’s blood serum. Next the horse is
 bled. Its serum is found to have acquired the power of protecting a
 guinea-pig against doses of the toxine of diphtheria which would
 otherwise be fatal. Ten times the quantity of the horse’s serum which
 will protect a guinea-pig (of 250 grammes weight) against ten times
 the minimum fatal dose of the toxine is called an antitoxic unit.

The treatment of diphtheria in man by the antitoxic serum thus obtained
has proved to be remarkably successful. Furthermore, if a susceptible
person who has been exposed to the infection of diphtheria, is injected
with a small dose of antitoxic serum, he becomes temporarily immune,
and does not fall a victim to diphtheria. This is a most important
point especially for young children, who may already be incubating a
disease which but for this prophylactic injection might occur and prove


This disease was formerly known as spotted or jail-fever, and for many
ages has been the scourge of prisons and armies, and all collections
of people living in overcrowded and insanitary districts. The history
of typhus is the history of human misery. It is essentially associated
with filth, overcrowding, and destitution; but when once established
by these conditions, it can be carried by infection to others who
live amidst healthy surroundings. It generally occurs in winter, when
overcrowding is greatest. With free ventilation, the disease cannot be
carried more than a few feet. It can be transmitted by clothing. The
micro-organism causing it has not been discovered. With the clearance
of the rookeries of our great towns, it is rapidly decreasing, and
appears likely to become extinct. The _means of prevention_, in
addition to the abatement of nuisances, including overcrowding, are
isolation and disinfection (pages 319 and 325).


This disease was formerly common in this country, but except in
some parts of Ireland has entirely died out. It is caused by a
micro-organism (_Spirillum Obermeieri_) which can be detected in the
blood. Inoculation of this will produce the disease in man or in

Epidemics of relapsing fever commonly follow in the track of typhus
fever; overcrowding and filth being especially associated with typhus,
and starvation with relapsing fever, hence its name of “famine fever.”


Enteric fever causes its highest death-rate in early adult life,
though it is not peculiar to any age. Eberth in 1880 discovered the
_Bacillus typhosus_ in the spleen and other organs of enteric fever
patients. This is commonly known as Eberth’s bacillus, and is the cause
of enteric fever. A few years later it was isolated and can now be
grown on agar or gelatine in laboratories. It closely resembles other
bacilli which are normal inhabitants of the human intestine; but can
be distinguished by certain tests. It is a small rod, rounded at its
ends, and from 2 to 4 µ long and three times as long as broad. In the
living state it is freely motile, and possesses a number of minute
cilia or flagella. Apart from other means of distinction between it
and other bacilli, _Grüber’s serum reaction_ enables its identity to
be ascertained. The bacillus suspected to be the _Bac.-typhosus_ is
cultivated in broth in the bacteriological laboratory. A small quantity
of blood is taken from the finger of a patient known to be suffering
from enteric fever. The serum is separated from the blood corpuscles
of this blood by a centrifugalising machine. A drop of the blood serum
is diluted with 100 drops of broth culture of the suspected bacillus.
If the latter is not the _Bac.-typhosus_, the individual bacilli when
a drop of the mixture is examined under the microscope, will continue
to move about freely; if it is the _Bac.-typhosus_, the bacilli will
adhere together in “clumps” and become immobile. Conversely a valuable
means of ascertaining whether a suspected case is really suffering from
enteric fever is secured, as this blood added to 30 times the amount of
a pure culture of the _Bac.-typhosus_ in broth will cause the latter to
“clump” within half-an-hour (_Widal reaction_). Higher dilutions are
usually unnecessary.

The chief means of spread of enteric fever is by the urine and fæces;
and nurses who have to empty bed-pans unless very careful to wash
their hands afterwards, using the nail-brush, are very liable to
become infected, probably when eating food afterwards. The urine in a
considerable proportion of cases, contains the typhoid bacilli, and
it is therefore most important that care should be exercised in the
cleansing of all chamber utensils, and that the urine as well as the
fæces should be rigidly disinfected (see page 331). The infectivity
of enteric fever has been underrated in the past. When patients with
this disease are nursed at home by relatives who do not appreciate the
full importance of the necessary precautions, it is rather the rule
than the exception for them to fall victims to its infection. Probably,
sometimes the infection has been scattered as dust, owing to small
particles of fæces or of urine having become dried on bed linen. The
most absolute cleanliness is essential in nursing this disease. In hot
climates there is reason to believe that infective dust may be blown
about from privies.

_Insanitary local circumstances_ are an important means of spreading
enteric fever. It is more prevalent where there are privies than
where there are pail-closets; and more prevalent where there are
pail-closets, than where water-closets are the rule. Defective drains
or soil-pipes are frequently found in houses in which enteric fever
originates, and there can be little doubt that the former are at least
partially responsible for the latter. The exact link is doubtful.
Probably infective dust is blown or aspirated into the room and is

The most common cause of enteric fever is _infected food or water_.
Of foods _milk_ not infrequently has been the means of spread of
enteric fever. Large epidemics have been traced to this source.
Usually this has arisen by washing the milk cans with or wilfully
adding contaminated water to the milk. _Water_, whether added to milk
or taken independently, must have contained the specific contagium
(the _Bac.-typhosus_) of enteric fever, to enable it to cause enteric
fever. Hence water from a contaminated stream is more likely to have
produced this effect than well-water, unless a patient has had enteric
fever in the house to which the well is attached, and his dejecta
have contaminated the water. Surface waters or spring waters may be
contaminated with sewage (as at Maidstone) or deep well waters through
fissures (as at Worthing) and thus widespread epidemics be produced.
After floods, rivers and wells are most likely to contain the specific
contagium of enteric fever, as at such times surface impurities from
middens, etc., are apt to be washed into the water. (See also pages 91
and 224).

The _means of prevention_ of enteric fever are the discovery and
removal of the cause of an outbreak, and the isolation of each patient
and disinfection of all discharges. An early means of diagnosis is
secured by Widal’s reaction. This is especially useful in cases not
presenting characteristic clinical symptoms. The recognition of a
disease or at least the suspicion of its presence is an indispensable
first step for the taking of precautionary measures.


Cholera, which was formerly so prevalent, now seldom occurs in this
country, and at each successive visit to England its inroads have
become less serious. At its last visit in 1893 it scarcely obtained
a footing in the country. Thus in the epidemic of 1854 in England it
caused 1080, in that of 1866 it caused 672, and in that of 1893 only
45 deaths per million of population. In this country at least it is
chiefly spread by infected water and foods, especially by infected
water; and the preceding figures form an excellent testimony to our
improvement in this respect. For particulars of the Hamburg outbreak,
see page 93. In its mode of prevalence and propagation it is very
similar to enteric fever, being infectious by means of the evacuations.
The means of prevention are the same as for enteric fever. Cholera was
shown by Koch to be caused by what is known as the _comma bacillus_ or
_spirillum_ of Asiatic cholera, so called because of its curved shape.
It is from 1·5µ to 2·6µ long and ·5µ broad. For the supposed connection
of enteric fever and cholera with movements of the ground-water, see
page 225.


is a most fatal disease among infants in the third quarter of
each year. It is chiefly a disease of urban life, and occurs to a
preponderant extent among the children of the artisan and still more
of the unskilled labouring classes. It is much less abundant in towns
which have adopted the water-carriage system of sewage than in those
retaining the conservancy methods of removal of excrement (page
198). Towns with the most perfect domestic and street scavenging
arrangements have the least epidemic diarrhœa. An impervious soil
favours a low diarrhœal mortality; while persons living on porous
soils usually have much diarrhœa. I have shewn elsewhere that given
two towns equally placed so far as social and sanitary conditions are
concerned, their relative diarrhœal mortality is proportional to the
height of the temperature and the deficiency of rainfall of each town,
particularly the temperature and rainfall of the third quarter of each
year. In other words there is a general inverse relationship between
rainfall and diarrhœa and a direct relationship between temperature and
diarrhœa. Thus wet and cool summers are adverse to diarrhœa. Ballard
concluded that the summer rise of diarrhœal mortality does not commence
until the mean temperature recorded by the 4-foot earth thermometer
has attained somewhere about 56° F., no matter what may have been the
temperature previously attained by the atmosphere. This is a convenient
index, as the summer warmth does not immediately cause diarrhœa. All
the above facts point to the conclusion that the fundamental condition
favouring epidemic diarrhœa is an unclean soil, the particulate
poison from which infects the air, and is swallowed most commonly
with food, especially milk. Thus, diarrhœa, like enteric fever, is a
“filth-disease.” As the contagium appears to gain entrance by food, the
following card of precautions which is distributed each year in the
poorer districts of Brighton may be reproduced here:


 During the summer a large number of infants die from diarrhœa.
 Scarcely a single baby who was being suckled dies from this cause.
 It is evident, therefore, that in the prevention of this very fatal
 summer disease, precautions as to food are most important.

 Attention to the following points would save many infants’ lives:—

 1. _Do not wean your infant during the hot months_ of July, August
 and September. To begin artificial feeding during hot weather is very

 2. If feeding by hand is absolutely necessary, carefully follow these

 (_a_) _All milk should be boiled_ before being given to the infant.

 (_b_) The infants’ food must be _prepared fresh each time_. (For
 particulars see below.) Milk and water, and still more “pap” or patent
 foods, if left two or three hours, “go bad,” and are then very highly
 dangerous to the infant.

 (_c_) _All jugs_ or other utensils used _for storing milk must be
 scalded out_ and kept absolutely clean. They should be covered to
 prevent access of dust.

 (_d_) _The feeding bottle must be thoroughly scalded after each meal_,
 and the tube thoroughly cleansed. It is best to use alternately
 two boat-shaped bottles without tubes. If the bottle smells sour,
 something is not clean, and the infant will suffer.

3. _Decomposing refuse_, such as decaying vegetables, bones,
fish-heads, &c., _is a fertile source of Diarrhœa_. _It should be
burnt_, and not placed in the dust-bin.

4. _Scrupulous cleanliness_ of the house, especially of the rooms where
food is stored, is most important. Dust in every form is dangerous to
health, and for removing it wet cleansing is preferable to dry. Thus
washing and scrubbing are safer means of cleansing floors, &c., than

5. _Report to the Sanitary Office_, Town Hall, any smells or choked
closet or drain.


  =For a Child aged=         =Mix and then boil=      =For each Meal=
                             (1 part _fresh_ milk )
  Under 6 weeks              {2 parts water       }  4 tablespoonsful.
                             (1 teaspoonful cream )

                             =Mix and then boil=
                             (1 part fresh milk   )
  6 weeks old                {1 part water        }  8 tablespoonsful.
                             (2 teaspoonsful cream)

                             =Mix and then boil=
                             (2 parts fresh milk  )
  From 3 to six months old   {1 part water        }  8 tablespoonsful.
                             (2 or 3 teaspoonsful )

The infant should _be fed at regular intervals only_, at first every
two hours, the interval being gradually increased.

The infant should _be fed slowly_.

If the milk as prepared above disagrees, _freshly boiled barley water_
should be used instead of water.

The _addition of cream is necessary_ because cows’ milk is poorer in
cream than mothers’ milk, and because it is very often made poorer
still by mixing with separated milk before sale. _Deficiency of cream
causes rickets._ A little sugar may also be added to the milk, but this
must not be regarded as a substitute for the cream.


Tetanus or lockjaw is not infectious, but is conveyed to man by the
inoculation of a wound by dirt or earth which contains the tetanus
bacillus. For this reason it is more apt to follow injuries to the
hands or feet. Extreme cleanliness of wounds is the only practicable
preventive means. Little is known of the history of the tetanus
bacillus outside the body; and as to what soils contain it most
abundantly. Wounds contaminated by horse manure appear to be especially


Glanders is common in horses. It attacks the mucous membrane of the
nose, causing ulceration. It is extremely infectious. =Farcy= is a more
chronic form of the same disease, in which the so-called “farcy-buds”
are produced. Its prevention can best be ensured by killing both
actually diseased and suspected animals, if the latter give a reaction
to mallein. _Mallein_ is a product allied to tuberculin, obtained from
cultivations of the bacillus of glanders. It sets up febrile reaction
in glandered, but not in healthy horses. Further preventive measures
are the temporary closing of public drinking fountains for horses, and
the thorough cleansing and disinfection of stables. Men, especially
grooms, are sometimes infected by the horse, and the disease is
commonly fatal.


Hydrophobia is the disease in man which is caused by the bite of a
dog or other animal suffering from =rabies=. It is seldom if ever
communicated otherwise than by inoculation. The _incubation period_ in
the dog varies from three to six weeks, and in man is usually about the
same; but occasionally it is much longer, occasionally even more than a

At the Pasteur Institute, Paris, patients who have been bitten by rabid
dogs are treated by the inoculation of an attenuated virus of rabies
derived from rabbits, with promising results.

Dogs only acquire rabies from dogs or other animals already rabid.
So far as is known, it does not arise _de novo_. Hence the necessity
for an extensive area of muzzling when cases of rabies occur. The
enforcement of this plan has greatly reduced the amount of hydrophobia
in this country in recent years. There has been much misplaced sympathy
with dogs on this score. In the dog the symptoms of rabies occur in
three stages: a _premonitory_ stage, in which the dog’s habits change,
he becomes morose and quiet, and dribbles; a _second_ stage, in which
he has paroxysms of fury, his voice is high-toned and croupy, and he
cannot swallow water; and a third or paralytic stage, in which his jaws
drop, he drags his hind legs and soon dies.


Erysipelas occurs on various parts of the skin. It is caused by the
inoculation through an abraded surface of a virulent form of the same
streptococcus that commonly causes suppuration. It occurs chiefly in
debilitated subjects. Some persons are specially prone to it, and may
have many attacks. Erysipelas, like scarlet fever, occurs most in years
in which there is deficient rainfall; and is probably conveyed by dust.
It may spread, though exceptionally, from case to case.


Yellow fever never occurs in England, except when imported from the
West Indies or other countries in which it is endemic. It clings to
seaport towns in hot countries; and as a permanent disease is only
found when the mean winter temperature is at least 68°-72° F. A frost
always stops an epidemic of this disease. The germs of this disease
are communicated by mosquitoes, which act as an intermediate host. Dr.
J. W. Lazear, although isolated from yellow fever cases, died of it
seven days after submitting to the puncture of an infected mosquito,
thus proving the communicability of this disease, and entitling himself
to an honoured position among scientific martyrs.


Plague is an Eastern disease, which occasionally shows a tendency
to become widely epidemic. It is due to a rod-shaped bacterium,
averaging ·8 µ to 1·6 µ in length, which does not form spores. In
its characteristic form patients suffering from this disease have
inflammatary swellings (buboes) of various glands: hence the name
_Bubonic Plague_. In other cases it simulates ordinary pneumonia,
typhus or septicaemia; or the patient may be so slightly ill as to
be able to walk about. It appears probable that the bacillus enters
the body through cracks or other lesions of the skin, possibly also
by inhaling infective dust. The rat is an important factor in the
spread of plague. Very commonly plague has been widely prevalent and
fatal among them before it attacks human beings. Rats also bring it in
ships from infected ports. Hence one of the most important preventive
measures is to kill all rats on board ship, before the cargo is
unloaded. This has been done by sulphurous acid fumigation in the
holds. The use of carbonic oxide gas will probably be found practicable
for the same purpose. Manson has put the importance of this point
tersely as follows: “To prevent cholera the tea-kettle, malaria the
mosquito net, and plague the rat-trap.” Flies may carry the infection
(page 281). It has been suggested that the fleas of rats carry the
infection (page 281).


Anthrax is a very fatal disease in cattle and sheep, occasionally
in pigs. Butchers may inoculate themselves with it when dressing a
diseased carcase; the tanners similarly when handling the hide; and
woolsorters may inhale it when sorting wool derived from a diseased
animal (page 107). To prevent the latter, suspected wool must be
disinfected by steam, and special arrangements made for carrying off
the dust produced during sorting.


occurs after childbirth. It is caused like erysipelas by the
inoculation of septic material. This may be conveyed by dirty
instruments (syringes, etc.), or by dirty hands. Hence the importance
of extreme cleanliness of hands, finger-nails, and all articles used
during and after childbirth.


has been commonly attributed to a damp condition of the atmosphere and
soil. I have elsewhere shown that this is a mistake, probably arising
from the fact that these conditions produce what are called “rheumatic”
pains, though they have no true relationship with acute rheumatism
(rheumatic fever). I have shown that rheumatic fever occurs chiefly in
very dry years, the excess of prevalence in such years being sufficient
to justify the use of the term “epidemic.” There is strong reason to
believe that rheumatic fever is an infective disease, derived, not from
other patients suffering from the same disease, but from some outside
micro-organism which is ordinarily saprophytic. It follows the rule
that when the lesion produced by an infective disease is deepseated
(in the joints in this instance), no infection can be communicated to
other persons. Some families are much more prone to rheumatic fever
than others.


is, like diphtheria, a somewhat mysterious infectious disease. Like
the latter it almost disappeared for a series of years, and then again
became epidemic in 1889. The previous epidemics of influenza in the
19th century had occurred in 1803, 1833, 1837-8, and 1847-8. The causes
of this recurrence of influenza are unknown. It is spread from person
to person by direct infection, the infection being conveyed by the
mucous discharge from the nose, throat, and lungs. Pocket-handkerchiefs
probably are largely responsible for conveying the infection as dust.
The disease is particularly fatal to the old; and these should not
expose themselves to possible sources of infection, as in public places
of assembly, during an epidemic. Every patient attacked with the
disease should remain indoors for at least ten days. This is in his own
interest, as he thus minimises the risk of such dangerous complications
as pneumonia; and it is his duty in the interest of the rest of the
community. Many lives might have been saved, had not influenzal
patients “struggled about” during the early stages of the disease.


=Malaria=, or =Ague=, is a generic name given to a disease caused by
the invasion of the body by the _plasmodium malariæ_, discovered by
Laveran in 1880. It occurs in two chief types, remittent fever and
intermittent fever. For many generations it has been regarded as due
to a marshy condition of the soil, associated with decaying vegetable
matter, and a moderately high temperature. It is now clear that these
conditions are necessary, only because they are necessary for the
life of the mosquito. The well-known danger of being out of doors at
night in a malarious country is explained by the nocturnal habits of
the mosquito. The higher salubrity of the upper stories of houses is
explained by the fact that the mosquito does not rise high from the
ground; and of high-lying localities by their greater dryness. The
value of the mosquito net, of smoke, and of fire as protections from
malaria are due to their keeping mosquitos at a distance. The mosquito
clings to the puddle or swamp where she was born, and where she will
deposit her eggs. Hence the special danger of the immediate vicinity
of such collections of water. Thus the prevention of malaria resolves
itself chiefly into means for preventing the development of certain
species of Anopheles (page 282). The conditions necessary for the
multiplication of these are (1), an atmospheric temperature from 75°
to 104° F.; (2) collections of fresh or slightly brackish water; and
(3) the presence in these of low forms of animal and vegetable life. We
have already described the cycle of life of the _plasmodium malariæ_
(page 282). Man is the chief, if not the only source, from which
the mosquito derives this parasite. In native communities the young
children, even when apparently not ill with malaria, nearly always
harbour these parasites in their blood corpuscles. Hence the importance
of Europeans having their dwellings as remote as possible from native
houses. Mosquitos do not travel far.

Instances of the prevalence of malaria in the absence of mosquitos are
not substantiated. The outbreaks of malaria where the soil has been
disturbed after long lying uncultivated, probably mean the formation of
puddles favourable to the breeding of the larvæ of mosquitos.

The necessary preventive measures are classified by Manson as:

  1. Suppression of mosquitos.
  2. Prevention of infection of mosquitos.
  3. Prevention of infection by mosquitos.

The =suppression of mosquitos= involves the draining or filling in of
swamps and ponds, the cleansing and canalisation of sluggish streams,
and the afforestation of hills to prevent floods. Cultivation of rice
and other plants entailing the prolonged flooding of land should
be restricted to fields remote from dwellings. Subsoil drainage is
helpful. The “painting” of stagnant waters with petroleum, which should
be renewed every week or two, frees water for a considerable time from
the larvæ of mosquitos. Eucalyptus and other balsamic trees may help to
dry up pools, &c.

The =prevention of infection of mosquitos= is secured by insisting on
all malarial patients using mosquito nets. This prevents the access of
mosquitos. At the same time patients should vigorously and persistently
take quinine, which kills the malarial parasites in the blood, and thus
diminishes and finally removes the danger to other persons produced by
the intermediation of the mosquito.

The =prevention of mosquito bites= is secured by rendering the house
mosquito-proof by filling in all openings by fine wire gauze, and by
having mosquito curtains to all beds; also by fumigating the rooms
occasionally with the dried flowers of the chrysanthemum, by strict
cleanliness of rooms, and by flushing them with sunlight. The proof of
the mosquito theory as to the causation of malaria has been recently
supplied by two test experiments. (_a_) In the first, a number of
mosquitos which had been fed on the blood of malarious patients were
sent to London from Rome. These were allowed to bite Dr. Manson’s
son, who had never previously had malaria. A few days later he had a
characteristic attack of fever. Malarial parasites were found in his
blood. He recovered in a week’s time after free dosage with quinine,
and the parasites disappeared from his blood. He suffered from a slight
relapse about a year later. (_b_) On a fever-haunted spot in the Roman
Campagna a wooden hut was built, and Drs. Sambon and Low, and three
others took up their abode here during the malarious season, the only
precautions taken being the use of mosquito nets and wire screens in
doors and windows. They went about the country daily, but were always
home before sunset. They all remained at the end of the season free
from malaria.




Consumption (also called _phthisis_ or _phthisis pulmonalis_) in
the year 1899 caused a recorded death-rate of 1,336, and tubercular
diseases of other parts of the body a death-rate of 575 per million
of the population. In the same year the chief infectious diseases,
including small-pox, measles, scarlet fever, whooping cough, typhus,
and enteric fever, and diphtheria, were together responsible for a
death-rate of 1,248 per million. In the five years, 1861-65, the mean
death-rate from consumption was 2,527 per million, so that a reduction
of nearly 50 per cent. has apparently occurred. Notwithstanding this
great decline, consumption and other consumptive diseases, which
may together be classed under the name =tuberculosis=, still cause
more deaths than all the acute infectious diseases put together. Its
importance is emphasised by the fact that between the ages of 20 and
45, one-third of all the deaths of males, and between one-third and
one-fourth of all the deaths of females occurring at these ages are due
to consumption of the lungs.

Formerly great stress was laid on the =hereditary character= of
consumption. It would appear, however, that what is inherited is
simply an increased vulnerability of tissues. Judging by the analogy
of other animals it may be said that infants are rarely, if ever, born
tuberculous. Bang examined 6,000 head of cattle with the tuberculin
test (see page 311), and found that in calves under 6 months old only
10·7 per cent. reacted, _i.e._ showed evidence of tuberculosis, between
6 and 12 months old 18·7 per cent., 1 to 2 years 23·2 per cent., and
over this age 31·3 per cent. reacted; from which it may be inferred
that the infection is nearly always received after birth.

The real cause of tuberculosis was shewn by Koch, in 1881, to be
the =tubercle bacillus=. This is a minute bacillus, the length of
which is from a quarter to half the size of a blood corpuscle.
These bacilli, obtained from tuberculous growths in the body, Koch
was able to cultivate on glycerine agar at blood-heat outside the
body. By sub-culturing he obtained pure cultures, and after growing
the bacilli for as long as fifty-four days, he inoculated various
animals, producing tuberculosis in every case, while in similar check
experiments in which all the conditions were the same, barring the
absence of bacilli, no tuberculosis resulted.

The tubercle bacilli are easily distinguished from most other bacilli
by the fact that after being stained by aniline dyes, such as
carbol-fuchsin, the colouration is not removed when the preparation
is soaked in dilute acid. By this means the presence of tubercle
bacilli in the sputum (expectoration) of a phthisical patient is easily
discovered, and a valuable means of early recognition of the disease
secured. This is most important, as in its early stages consumption is
an easily curable disease. Tubercle bacilli are discharged from the
lungs in consumption of the lungs, from the bowels in consumption of
the bowels, and so on. Hence the essential necessity for disinfecting
these discharges. Such discharges while in a moist condition have,
unless they are actually swallowed, little or no capacity for evil.
It is when they become dry that they become dangerous. Thus the
expectoration of a consumptive patient spat on to the floor or
deposited in a pocket handkerchief is, so long as it remains moist,
perfectly innocuous. What is evaporated from the wet surface is simply
steam, harmless as the steam escaping from the domestic tea-kettle.
But when it becomes dry, then comes danger. Dust is formed, which
contains the living tubercle bacilli, and with the mere shaking of
the handkerchief or the disturbance of the dust on the floor these
are inhaled, and often cause consumption. The person thus infected
may be a new patient. Often also it is the consumptive patient who is
thus re-infected. Consumptive patients tend to recover. But if the
patient’s disease is daily recruited by fresh doses of the tubercle
bacilli inhaled with the dust of previous expectoration, fresh centres
of disease are produced, and thus the patient is unwittingly helping to
cause his own death.

The =infectious character= of tuberculosis has been long suspected. In
the 18th century, in Naples, there were enactments insisting on the
isolation of consumptive patients and disinfection of their furniture,
books, etc. We now know, however, that these were counsels of panic,
and that for practical purposes the infection may be regarded as
confined to the sputum. The _expired breath is free from infection_
except during coughing. That the sputum is infectious can be easily
proved by feeding guinea-pigs or the domestic fowl on it. These rapidly
become affected by generalised tuberculosis. The simple character of
the precautions against infection which are required may be gathered
from the following copy of a card which is given to consumptive
patients in Brighton:—

 Precautions for Consumptive Persons.

 Consumption is, to a limited extent, an infectious disease. It is
 spread chiefly by inhaling the expectoration (spit) of patients which
 has been allowed to become dry and float about the room as dust.

 +_Do not spit except into receptacles, the contents of which are to
 be destroyed before they become dry. If this simple precaution is
 taken, there is practically no danger of infection._+ The breath of
 consumptive persons is free from infection.

 The following detailed rules will be found useful, both to the
 consumptive and to his friends:—

 1.—Expectoration indoors should be received into small paper bags and
 afterwards +burnt+.

 2.—Expectoration out of doors should be received into a suitable
 bottle, to be afterwards washed out with +boiling water+; or into a
 small paper handkerchief, which is afterwards +burnt+.

 3.—If ordinary handkerchiefs are ever used for expectoration, they
 should be +put into boiling water before they have time to become
 dry+; or into a solution of a disinfectant, as directed by the doctor.

 4.—+Wet+ cleansing of rooms, particularly of bedrooms occupied by sick
 persons, should be substituted for “dusting” and sweeping.

 5.—+Sunlight+ and +fresh air+ are the greatest enemies of infection.
 Every patient should sleep with his bedroom window +open+ top and
 bottom, a screen being arranged, if necessary, to prevent direct
 draught; and, if possible, occupy a separate bedroom. The patient need
 not fear going out of doors in any weather, if warmly clad.

 N.B.—The patient +himself+ is the +greatest gainer+ by the above
 precautions, as his recovery is retarded and frequently prevented by
 renewed infection derived from his own expectoration.

 6.—Persons in good health have little reason to fear the infection of
 consumption. Over-fatigue, intemperance, bad air, dusty occupations,
 and dirty rooms favour consumption.

The most common source of infection is undoubtedly the dried
expectoration. Infection may, however, probably be derived from
infected food, as milk or meat.

The danger from meat is much less than that from milk, because the
former is more generally cooked than the latter, and because the
diseased portions of the former would be at least partially removed
before it was sold. The conditions under which the =meat= derived
from tuberculous cattle should be destroyed are given on page 24. The
abolition of private slaughter-houses, the general establishment of
public abattoirs, and efficient meat inspection would do much towards
aiding in eliminating tuberculous cattle from herds; because it would
no longer be found remunerative to keep tuberculous cows until they
become seriously diseased.

The danger from infected =milk= is probably very great. This has
been repeatedly proved experimentally for bovine tuberculosis by
experimenting on calves and pigs. A cow may suffer from tuberculosis
of its udder, and yet go on freely secreting milk. The milk from such
an udder readily produces tuberculosis in calves or pigs drinking it;
but if another animal be fed during the same period with boiled milk
obtained from the same udder, it remains well.

The presence of tuberculosis in cattle can be determined with almost
complete certainty by the =tuberculin test=. A glycerine extract of
pure cultivations of tubercle bacilli (filtered so as to be free from
bacilli) was found by Koch to contain substances which, when injected
into guinea-pigs suffering from tuberculosis, produced a febrile
reaction, and appeared likely to cure the disease. So far as man and
larger animals are concerned the hope of cure by this means has
not been realised; but _as a means of diagnosis_, _i.e._ detection
of tuberculosis, injection of a small quantity of tuberculin under
the skin, has been found most valuable. If the cow thus injected is
suffering from the slightest tuberculosis, it becomes feverish for
a few days; if it is healthy no “febrile reaction” occurs. By using
this test tuberculous cattle can be detected, they can then be kept
in separate sheds, the former sheds cleansed and disinfected; the
milk of these cattle kept separate from that of the rest of the herd,
and boiled before being drunk, or the infected cattle sent to the
butcher. If the disease is strictly localised the carcases can be
utilised for food, after careful destruction of all diseased portions.
If these means were generally adopted, tuberculosis might gradually
be eliminated from the cattle of the entire country, and a serious
source of loss to farmers, as well as of danger to children drinking
the infected milk, removed. The presence of tubercle bacilli in cow’s
milk is detected by microscopic examination and by injection of small
quantities of the suspected milk into guinea-pigs. The proportion of
infected samples found when examinations of milk supplies have been
made in different towns has varied from 10 to over 50 per cent.

It is probable that tuberculosis is conveyed by cow’s milk only when
the tuberculous disease affects the udder. But inasmuch as the udder
of a tuberculous animal may become tuberculous very rapidly and
without being detected for a considerable time, it is evident that
_no tuberculous animal of any kind should be allowed to remain in any
cowshed where milch cows are kept_.

Recently (July, 1901) Koch has thrown doubt on the identity of bovine
and human tuberculosis, which was previously accepted, because (unlike
some other observers) he has been unable to produce in 19 cattle,
on which he experimented, tuberculosis by mixing with their food
expectoration of consumptive persons, or inoculating under their skins
similar material. Even if these negative results should subsequently
be confirmed, the converse proposition does not follow, that bovine
tuberculosis cannot be communicated to man; and apart from this
possibility milk containing the bacilli of bovine tuberculosis cannot
be regarded as wholesome.

The boiling of milk destroys tubercle bacilli. So does a temperature
considerably below 212° F. In Denmark, where butter and cheese are
manufactured on a large scale, and the raw milk is collected in central
dairies, a law was passed in 1898, obliging every proprietor of a dairy
to heat all skimmed milk, or butter milk, to a temperature of 85° C.
(185° F.) before returning it to the farms. _Pasteurization_, _i.e._
the heating of milk in a special apparatus to a temperature of 70° C.
(158° F.), and keeping it at this temperature for 30 minutes kills
tubercle bacilli. If it is rapidly cooled, the nutritive value and
taste of the milk are not spoilt. It is safer, however, to go beyond
this point, and the use of an apparatus like the Aylmer or Sentinel
Sterilizer can be recommended. More recent experiments have made it
doubtful whether tubercle bacilli in milk are always killed in milk at
a temperature of 70° C., the pellicle formed on milk when it is heated
appearing to shield the bacilli from the effect of the heat. Hence it
is desirable that “no sterilizer should be looked upon as thoroughly
efficient for the purpose in which a temperature of at least 85° C.
(185° F.) is not attained.”

The following test may be used to determine whether milk has been
efficiently pasteurized:—

 Natural milk contains a ferment or enzyme, which is destroyed at a
 temperature of 176° F. This enzyme splits up hydrogen peroxide (H₂O₂)
 into water and oxygen, but this effect is not produced in milk heated
 above 176° F. Take one drop of a dilute aqueous solution of hydrogen
 peroxide, add it to one teaspoonful of the milk. Next add two drops
 of a watery solution of paraphenyldiamine. A dark indigo colour is
 produced with uncooked milk, no change of colour if the milk has been
 pasteurized. The same test can be used for determining whether butter
 has been made with pasteurized milk.

Infection is not the sole determining cause of tuberculosis. Certain
conditions of environment may determine whether the infection will
succeed in “taking root” or not. Of these the following are important:

The _nutrition of the individual_ if defective favours infection.
Probably one chief reason why consumption has declined nearly 50 per
cent. in the last 50 years is the better, more varied and more abundant
food of the population.

_Improved housing of the population_ has greatly helped in the same
direction. Tubercular diseases increase with density of population,
and are most prevalent in overcrowded tenements. Probably overcrowding
chiefly acts by favouring direct infection, but it must also lower the
health and power of resistance of the individual against infection.

The _drying of the subsoil_ has been regarded as a chief cause of the
reduction of consumption (page 226). It is probable, however, that the
wet soil merely predisposed to consumption, because it was commonly
associated with cold and wet houses, which would favour catarrhs, and
open the way for the infection of consumption.

The _dryness of the house_ is a most important matter. If a damp soil
means also a damp house it must favour consumption and other chest
affections. Damp air, like water, rapidly abstracts heat from the body.
Compare, for instance, the discomfort of sitting clad in water at a
temperature of 65° F. with the comfort of sitting clad in a dry room at
the same temperature! The domestic fowl is naturally immune to anthrax;
but by being kept for a few hours with its feet in cold water, it can
be rendered susceptible to inoculation with this disease.

The _effects of breathing foul air_ are clearly shewn by the varying
death-rate from phthisis in different occupations. Thus, if the
comparative mortality figures of agriculturists be represented as 100,
that of a commercial clerk = 176, of a draper = 200, of a tailor = 211,
of a printer = 244, of a bookbinder = 246.

The _effects of breathing dust-laden air_ are even more marked. Thus,
if the comparative mortality figures from phthisis of agriculturists =
100, that of a coal-miner = 166, of a mason = 215, of a chimney-sweep
= 249, of a file-maker = 373, of a cutler = 407, of a potter = 453.
The last figure probably also shows the influence of alcoholism, which
greatly favours tuberculosis.

=Means for Preventing Tuberculosis.=—The means for preventing
tuberculosis from infected milk and meat have been already indicated.
They comprise—

 (_a_) Means of eradicating tuberculosis from cattle;

 (_b_) Means of preventing harm from tubercle bacilli in milk or meat;

Under the first head improved conditions of housing of cattle, greater
air-space, improved ventilation, a larger proportion of out-door life
are important. The use of the tuberculin test, the separation of
healthy from diseased cattle; the disinfection of sheds occupied by
infected cattle are also essential.

Under the second head come efficient sterilization of suspected food
(see p. 13), and the rejection of diseased meat. (See p. 24).

The most important measure against tuberculosis is the prevention of
infection from patients with consumption. Under this head are comprised
the following steps:—

 A. _Means of ascertaining the existence of the disease_—

  1. Bacteriological diagnosis.
  2. Notification of cases, voluntary or compulsory.

 B. _Direct preventive measures_—

  1. Law against expectoration in places of public resort.
  2. Disinfection and cleanliness.
  3. Isolation.
  4. General sanitary improvement.

 C. _Education of the public and of patients as to the importance of
 the preceding measures._

_The gratuitous examination of suspected sputum_ is now being
undertaken in certain towns. The earlier the infectious condition of
expectoration is detected, the sooner can the necessary precautions be

The _notification_ to the medical officer of health of all cases of
consumption I have repeatedly advocated. This is already carried out
for the chief acute infectious diseases, and although the difficulties
of acting on the information received in regard to a chronic disease
like consumption are considerable, they can be overcome with tact and
discretion. Voluntary notification is already practised in Brighton,
Manchester, and a few other towns. Notification gives increased
and more exact opportunities of preventing phthisis by—1. Enabling
disinfection and cleansing of affected rooms to be effected; 2.
Enabling instructions to be given to the patient and his relatives as
to the exact precautions required; and by 3. Facilitating the removal
of the insanitary conditions of home and work which may have caused the
case or favoured its untoward progress.

The following scheme of measures of disinfection was prepared by Drs.
Niven and Newman and myself for the National Association for the
Prevention of Consumption, and is issued by them in pamphlet form:—

 In preventing a consumptive person from spreading the disease,
 two sets of preventive measures are required:—1st, The removal
 or destruction of the infective matter already disseminated by
 the patient’s discharges, especially by his phlegm; and, 2nd, the
 prevention of future dissemination. For the latter purpose the main
 object is not to permit any discharge to become dry before being
 destroyed. Before the consumptive person has learned the personal
 precautions which must be taken, and up to the time when he has been
 trained to carry them out carefully, he has probably distributed a
 considerable amount of infective matter. This is especially liable
 to accumulate in a dangerous form at home, where the space is small,
 and light and ventilation are defective. Infective particles will be
 found in greater abundance on and near the floors, on ledges, and in
 room-hangings. But the personal clothing and bedclothes will also have
 become infected. Hence it is necessary to disinfect the floor, walls,
 and ceiling of the rooms occupied by the patient, as well as the
 furniture, carpet, bedclothes, &c.

 When this has been done, if the personal precautions advised are
 carried out by the consumptive, further disinfection should not be

 It is, however, difficult to make sure that personal precautions are
 fully carried out, and rooms should therefore be subsequently cleaned
 at least once in six months, the floors being scrubbed with soft soap,
 the furniture washed, the walls cleaned down with dough, and the
 ceiling whitewashed.

 Confined workshops in which a consumptive has worked for some time
 should be cleansed, and a notice in reference to spitting should be
 suspended in all workshops. The latter precaution should also be
 observed in all public-houses and common lodging houses, both of which
 require special attention to cleansing.

 Disinfection of rooms which have been occupied by consumptive patients
 may be secured in various ways, but the following are the practical
 rules which must underlie any methods adopted:—

 1. Gaseous Disinfection of Rooms, or “Fumigation,” as it is termed, by
 whatever method it is practised, is inefficient in such cases.

 2. In order to remove and destroy the dried infective discharges, the
 Disinfectant must be applied _directly to the infected surfaces_ of
 the room.

 3. The Disinfectant may be applied by washing, brushing, or spraying.

 4. Amongst other chemical solutions used for this purpose a solution
 of Chloride of Lime (1 to 2 per cent.) has proved satisfactory and

 5. In view of the well-established fact that it is the dust from dried
 discharges which is chiefly infective, emphasis must be laid upon the
 importance of thorough and wet cleansing of infected rooms.

 6. Bedding, carpets, curtains, wearing apparel, and all similar
 articles belonging to or used by the patient, which cannot be
 thoroughly washed, should be disinfected in an efficient steam

 7. After all necessary measures of Disinfection have been carried out,
 the essential principle governing the subsequent control of a case
 of consumption is that all discharges, of whatever kind (especially
 expectoration from the lungs), should under no circumstances be
 allowed to become dry. #/

Besides measures of disinfection and cleanliness, the patient must be
placed under the best conditions for overcoming the disease. The same
measures tend to prevent infection. Thus abundant food, an open-air
life, sleeping with bedroom windows widely open, avoidance of dust,
abundance of sunshine, are all important. The importance of _sunlight_
in the prevention of consumption can scarcely be exaggerated. Koch
found that tubercle bacilli were killed in from a few minutes to some
hours, according to the thickness of the layer in which they were
exposed to the sunlight. He found that even ordinary daylight produced
the same effect, if it lasted long enough; cultures of tubercle bacilli
dying in from five to seven days if exposed at the window in compact
masses. These experimental facts emphasise the importance of abundant
open space about dwelling-houses (see p. 203), the provision of a large
window-area (see pages 202 and 216), of staircase ventilation, and
lighting, &c.

=Scrofula= means a tubercular affection of the lymphatic glands. It
occurs most commonly in the neck. The infection is usually received
from some neighbouring mucous surface, as from the throat, being
derived from dried expectoration or diseased milk. The same indications
as for the prevention of phthisis hold good for scrofula.



We are confident from the actual discovery of the micro-organisms
causing certain infective diseases, that the other diseases of an
analogous nature are similarly caused by living contagia. On this
supposition, action is taken for the prevention of these diseases. This
action comes under a number of different heads, which may be classified
as follows:—

1. =Means for the early recognition of the infectious character of a
disease.= The bacteriological aids to recognition in diphtheria (page
299), enteric fever (page 301), and phthisis (page 310) have been
already mentioned. It is important to call in medical aid when any
suspicious symptoms arise, even when these symptoms do not appear to
be urgent. If an infectious disease is not recognised in its early
stage, it may be easily overlooked, and the patient cause a serious
epidemic. The following hints for teachers are in Brighton sent with
each circular letter as to excluding infected children from school. The
list is not exhaustive, but may aid in drawing attention to suspicious
symptoms. The only safe rule when in doubt is to _act as though a case
is infectious until a skilled opinion can be obtained_.


 As infection is sometimes spread by means of children attending school
 while suffering from undetected infectious diseases, the following
 hints may be useful to the teacher:—

 1. Any scholar having a sore throat should be sent home and regarded
 as infectious until the throat has been examined by a doctor.

 If a scholar has enlarged glands in the neck, and especially if he or
 she is very pallid, the suspicion of possible diphtheria should be
 entertained. Many slight cases of diphtheria escape detection.

 2. Any scholar suffering from a severe cold, with sneezing, redness
 of the eyes and running at the nose, should be sent home. It may
 mean an influenza cold or the commencement of measles, and both are
 infectious. This recommendation is particularly important when measles
 is known to be prevalent.

 3. A child with a violent cough, especially if it is severe
 enough to cause vomiting or nose-bleeding, should be suspected of
 whooping-cough, and sent home, even if the characteristic “whoop” is
 not heard.

 4. Slight cases of scarlet fever sometimes escape notice, and the
 patients are sent to school with the skin on the hands, etc., freely

 5. In any of the above instances, or any other case of suspicion, the
 Medical Officer of Health, on receiving a confidential intimation,
 will be glad to make an investigation.


  Sudden onset.
  Usually vomiting.
  Always headache.
  Feverish, with dry, hot skin.
  Sore throat.
  Red rash on chest in a few hours.


  Severe “cold in the head” for 72 hours before the blotchy rash
  appears. _Measles is extremely infectious in this preliminary stage._
  Consider every severe influenza cold as possibly measles.


  may be very indistinct.
  Languor and sore throat.
  Glands under and behind jaw are enlarged.
  Patient very pallid.
  White or yellow patches seen on examining inside throat.
  Whenever doubtful, send the scholar home.


 In a child under seven, a severe cough should always be regarded as
 possibly whooping-cough, although no “whoop” has yet been heard.

2. The =notification= of all cases of infectious diseases to the
medical officer of health, is clearly a means to an end, that of
securing that the preventive measures to be next named are effectively
carried out.

3. =Means for the production of an artificial immunity.= This is only
practicable at present for two diseases of this country, small-pox
by means of vaccination (page 293), and a temporary immunity against
diphtheria by a dose of antitoxic serum (page 299). Apart from these
means, any measures for improving the health of a child tend in the
same direction. Enlarged tonsils, “adenoids” at the back of the nose
(causing the child to snore at night and to breathe through his mouth),
discharges from nostrils or ear, and similar conditions should receive
early medical attention.

4. =Isolation=: preventing the conveyance of the contagium from the
sick to the healthy.

5. =Disinfection=, _i.e._ destruction of the contagium of the disease.

The Infectious Disease (Notification) Act, 1889, and the corresponding
London Act of 1891, impose a dual duty of notification (_a_) on every
medical practitioner attending on or called in to visit an infectious
patient, as soon as he becomes aware of its nature; and (_b_) on
the head of the family to which the patient belongs or the nearest
relative. The intimation must be sent by each of these to the local
medical officer of health, the practitioner being paid a small fee
for his trouble. Usually notification by the householder is only
enforced when no doctor is in attendance. The diseases to which this
Act applies are small-pox, cholera, diphtheria, membranous croup[11],
scarlet fever, erysipelas, and the fevers known by any of the following
names: typhus, typhoid, enteric, relapsing, continued or puerperal. The
list of notifiable diseases may be extended by resolution of the Local

The enforcement of notification is most important for the public
health. (_a_) It enables the medical officer of health to take
immediate steps to prevent the spread of infection, by enforcing proper
isolation of the patient, efficient disinfection, and by preventing
the attendance of children from infected houses, at school, etc. (_b_)
It enables the links of evidence connecting a series of cases to be
identified, _e.g._ cases due to a common milk supply, or attendance at
a particular school. (_c_) It has a valuable educational effect on all
concerned in the cases.


Both the patient and his attendant need to be isolated in diseases like
scarlet fever, diphtheria and small-pox. The rule is less absolute
in enteric fever. In the following description the standard of
requirements taken is that of the most dangerous infectious disease,
small-pox. The first point to decide is whether the patient may be
safely isolated at home. For small-pox this ought never to be allowed
in a town. For other diseases, this may be permitted, if the following
conditions can be fulfilled.

For =Isolation at Home= a couple of rooms are required, preferably
on a higher floor or in a detached wing of the house. The w.c. used
for the dejecta of the patient must not be used by any other members
of the household. All linen, towels, handkerchiefs, etc., should be
immersed in actually boiling water containing some washing soda, before
leaving the sick-room. Other articles to be washed, if they will be
deteriorated by soaking in boiling water or a chemical disinfectant,
must be tightly wrapped in bundles, and covered with a clean wet sheet
saturated with a strong disinfectant solution (page 331). Solid and
liquid excreta, expectoration and other discharges must be treated
as described on page 331. The nurse should not eat her meals in the
patient’s room. She should wear a cotton dress to be changed before
going out for a walk. Her hands must be thoroughly washed and brushed
after handling or helping the patient, particularly in enteric fever.
It is advantageous if the nurse has previously had the patient’s
complaint. Attention on the part of the nurse to minute detail is
essential, especially in view of the possibility of receiving infection
from infected articles as well as directly from the patient. The
measures required for the subsequent disinfection of the sick-rooms and
of clothing, bedding, books, etc., are given on page 332.

The use of =hospital isolation= has rapidly increased in recent years,
thus releasing private families from a serious burden. The number
of beds which a Local Authority should supply for their district is
usually stated as one for every 1,000 inhabitants, but in poorer
districts this does not suffice. The site of the hospital should be
well removed from houses. There must be a minimum zone of 40 feet
between all infected buildings and the boundary walls, and the same
distance between neighbouring buildings. A wall at least 6 ft. 6 in.
high should enclose the hospital site. The hospital is divided into
separate detached pavilions for the treatment of different infectious
diseases. A floor space of 156 square feet should be allowed for each
bed. The height of the ward should be about 13 feet, its width from 24
to 26 feet, and the total cubic space for each patient should be 2,000
cubic feet for scarlet fever, 2,500 for diphtheria. The lavatories and
water-closets are separated from the main ward by a cross-ventilated
lobby. In an isolation hospital every surface should be washable; all
corners should be rounded off, and all projections on which dust can
lodge avoided. The proportion of window space should be about 1 square
foot to every 70 cubic feet. Special isolation pavilions are required
for cases of doubtful diagnosis. The ventilation and warming of wards
must be carefully regulated. Cross-ventilation by windows open on
opposite sides of the ward can be maintained in nearly all weathers.
The temperature of the ward should be maintained at 55°-60° F.

=Ambulances= are usually provided by the Local Authority for the
removal of infectious patients. The ambulance should be cleansed and
disinfected after each journey. The use of private conveyances for
infectious patients is forbidden, except under special limitations.

The =hospital isolation of small-pox= is beset with special
difficulties. There is a considerable body of evidence indicating
that small-pox may be aerially carried from patients in hospitals
to people living within a zone of half a mile, or possibly further.
Without accepting the view that aerial dissemination of small-pox
to considerable distances from the patient frequently occurs, it
still remains true that, either by this means or by errors in the
administration of small-pox hospitals, they do frequently constitute
a source of danger to persons living in the vicinity. The Local
Government Board recommended that a Local Authority should not
contemplate the erection of a small-pox hospital. (_a_) On any site
where it would have within a quarter of a mile of it as a centre either
a hospital, whether for infectious diseases or not, or a workhouse, or
any similar establishment, or a population of 150-200 persons; (_b_)
on any site where it would have within half a mile of it as a centre a
population of 500-600 persons, whether in one or more institutions or
in dwelling-houses.


This term has been chiefly employed to denote the limitation of the
movements of vessels coming from infected ports, for a term which, as
the name indicates, was formerly forty days, but is now shorter. It may
be conveniently employed, however, to signify the restriction of the
movements of all persons who have been apparently exposed to infection,
or who continue to live in infected dwellings. In this sense we may
speak of:

  1. Domestic Quarantine.
  2. Scholastic Quarantine.
  3. National and International Quarantine.

=Domestic Quarantine=, to a varying extent, is desirable for the
members of a family of which one member has been attacked by an
infectious disease. For small-pox every member of a household should be
kept under strict watch until sixteen days have elapsed since the last
contact with the case of small-pox, or until successful vaccination has
been secured. For enteric fever this strict watch would be unnecessary,
but the remaining members of the household should be warned to call in
a doctor on the first symptom of malaise.

Quarantine is specially indicated for certain occupations. Thus if
the child of an out-door labourer had been removed to a hospital with
scarlet fever, it would be unnecessary to keep the latter away from
work during the following week. If, however, he were a milk-carrier,
or a tailor, or an assistant in a sweet-stuff shop this would be a
desirable measure.

The =Quarantine of School Children= is more necessary than that of
adults, because the former are more susceptible to infection. Children
are kept from school:

(_a_) Because the infectious patient still remains in the house.
In this case the healthy children must be kept from school until
the patient has ceased to be infectious and disinfection has been
thoroughly carried out; and for a further period longer than the
longest known period of incubation of the disease in question (page
287), a margin being left for contingencies. It would probably be 8
_plus_ 2 weeks for scarlet fever.

(_b_) Children are kept from school for a period exceeding the longest
period of incubation when the patient has been removed to hospital.

The table on page 322, modified from the Author’s _School Hygiene_, is
introduced as furnishing a convenient summary of the subject.

Objection is sometimes taken to the exclusion of children under the
above circumstances from school, on the ground that they continue to
mix with others in the street or in neighbouring houses. Clearly,
however, in a school-room, a suspected child may communicate infection
to children coming from widely scattered streets, while out-of-doors
the danger is comparatively slight, and among neighbours the danger is
very limited in area.

It is assumed in the following table that all infected articles have
been disinfected before the termination of the period of quarantine.

  │             │                     │                     │ DURATION OF│
  │             │                     │   DATE AT WHICH     │ QUARANTINE │
  │             │                     │       SCHOOL        │ OF CHILDREN│
  │             │    DURATION OF      │   ATTENDANCE MAY    │  EXPOSED TO│
  │  DISEASE.        INFECTION.       │     BE RESUMED.     │ INFECTION. │
  │_Scarlet     │From 5 to 8 weeks;   │Not less than 8 weeks│14 days.    │
  │ fever_      │ ceases when all     │ from the beginning  │            │
  │             │ peeling of the skin │ of the rash, and    │            │
  │             │ has been completed, │ then only if no sore│            │
  │             │ and when the child  │ throat or sore      │            │
  │             │ is free from        │ places.             │            │
  │             │ discharge from the  │                     │            │
  │             │ nose or ear or sore │                     │            │
  │             │ places.             │                     │            │
  │             │                     │                     │            │
  │_Diphtheria_ │ At least 21 days;   │Not less than 2      │12 days.    │
  │             │ often much longer.  │ months, and not     │            │
  │             │ Absence of infection│ then if strength not│            │
  │             │ should be confirmed │ recovered, or if any│            │
  │             │ by bacteriological  │ sore throat or any  │            │
  │             │ tests.              │ discharge from nose,│            │
  │             │                     │ eyes, ears, etc.    │            │
  │             │                     │                     │            │
  │_Small-pox   │About 4 to 5 weeks   │When every scab has  │18 days.    │
  │ and Chicken │                     │ fallen off.         │            │
  │ pox_        │                     │                     │            │
  │             │                     │                     │            │
  │_Measles_    │From 3 to 4 weeks;   │Not less than 4 weeks│21 days.    │
  │             │ when all cough and  │ from beginning of   │            │
  │             │ branny shedding of  │ rash.               │            │
  │             │ skin has ceased.    │                     │            │
  │             │                     │                     │            │
  │_Rötheln     │2 to 3 weeks         │From 3 to 4 weeks    │21 days.    │
  │(German      │                     │ from beginning of   │            │
  │  measles)_  │                     │ rash.               │            │
  │             │                     │                     │            │
  │_Mumps_      │About 21 days from   │4 weeks from the     │24 days.    │
  │             │ the beginning.      │ beginning.          │            │
  │             │                     │                     │            │
  │_Whooping    │6 weeks from the     │In about 8 weeks     │21 days.    │
  │cough_       │ beginning of        │                     │            │
  │             │ whooping, or when   │                     │            │
  │             │ the cough has quite │                     │            │
  │             │ ceased.             │                     │            │
  │             │                     │                     │            │
  │_Typhus and  │4 to 5 weeks         │When strength        │28 days.    │
  │ enteric     │                     │ sufficient.         │            │
  │  fevers_    │                     │                     │            │
  │             │                     │                     │            │
  │_Influenza_  │2 to 3 weeks         │1 month              │10 days.    │

=School Closure= is occasionally required to prevent the further
spread of an infectious disease. This can be enforced on the order of
any two members of the Local Sanitary Authority acting on the advice
of the medical officer of health. This ought to be only occasionally
necessary if notification of infectious diseases is strictly enforced,
and if suspicious individual children are excluded from attendance
at school. In diphtheria school closure may occasionally be rendered
unnecessary by systematic bacteriological examination of the throats
of children who had been exposed to infection (see page 299). School
closure is more useful for country than for town schools, as in the
former the homes of children are more remote from each other, but it
is occasionally necessary for both. For measles school closure is
specially indicated in Infants’ Schools. We have already seen that
this disease is chiefly fatal when caught at a tender age (page 297).
The early closure of Infants’ Schools, and particularly of the Babies’
Class is therefore indicated. It is unfortunate that the attendance at
school of children under six years of age is encouraged. Such children
have more severe and more frequently fatal attacks of diphtheria,
scarlet fever, measles, and whooping-cough; and these are frequently
acquired at school.

=International Quarantine= was originally enforced against plague; but
in many countries has been extended to other diseases, as cholera,
yellow fever, typhus fever, small-pox and leprosy. In England cholera
is the only disease in connection with which it has been in the past
enforced. It has now been entirely abandoned. It consists in the
compulsory isolation at the port of entry of all persons who have come
from an infected district, or have been in contact with a case of the
infectious disease against which quarantine is enforced, for a length
of time which will enable it to be determined whether the persons
detained are or are not incubating the disease. If this measure could
be strictly enforced, and if infectious diseases were conveyed only
by infectious persons, quarantine would undoubtedly be effective.
But in practice quarantine cannot be enforced in Europe; and as it
cannot be efficiently enforced it forms an ineffective and irrational
derangement of commerce. Thus if plague prevailed in France it would be
impracticable to detain for ten or twelve days every person entering
England. Furthermore, in this instance, infection is brought by rats as
well as persons; and measures effective for the latter do not prevent
the former from importing infection. Because of its impracticability
and of the disorganization of commerce which would be associated with
any attempt to enforce it, England has abandoned quarantine and other
countries are gradually following its example. England bases its
action on the ground that (_a_) _sanitation is the true chief means of
defence_, especially against cholera. It does not trust to this alone
but to this along with (_b_) _medical inspection_ at the ports, (_c_)
and _subsequent medical supervision_ of persons landed from suspected
vessels. By these means a watch can be kept over persons who have been
in contact with infection.

Regulations are issued at intervals by the Local Government Board
requiring the disinfection by steam of all rags and similar materials
imported from towns in which small-pox, cholera, etc., are prevalent.



By disinfection is meant the destruction of the active cause of each
infectious disease. A disinfectant is therefore synonymous with a
_germicide_. Disinfectants must be distinguished from _deodorants_
or deodorisers, such as charcoal, and from _antiseptics_, which are
antagonistic to the growth of bacteria, without necessarily killing
them, _e.g._ common salt. Disinfection may be effected by chemical or
physical means.


A chemical disinfectant should fulfil the following conditions: 1. It
must be an efficient germicide. 2. Its germicidal power should not
be destroyed by the fæcal or other polluting matter, with which the
bacteria of infection are associated. 3. For many purposes, it must
not be destructive to or liable to stain the skin, or fabrics, or
other articles to which it is applied. 4. It should preferably not be
a virulent poison; and should be moderately cheap. The search for a
completely non-poisonous disinfectant is a chimera.

There are three great =classes of chemical disinfectants=.

1. Oxidising agents, as the halogens (chlorine, etc.) and permanganates.

2. Deoxidising agents, as sulphurous acid (SO₂) and formic aldehyde

3. Other disinfectants, which act by coagulating protoplasm or
otherwise, as carbolic acid, corrosive sublimate.

The number of disinfectants is legion. Only the chief ones can be
mentioned and their chief properties described. It is a good rule to
eschew the use of all disinfectants of which the exact composition is
not given; and all disinfectants which are described by “fancy” names,
which are not descriptive of their composition.


=Chlorine= has been most commonly used as chloride of lime (CaCl₂,
Ca(ClO)₂). This is somewhat unstable in composition. A solution of
sodium hypochlorite containing 10 per cent. of available chloride is
preferable. Chloride of lime for sprinkling on decomposing matter
should contain at least 10 to 15 per cent. of available chlorine.
Sulphuretted hydrogen and other offensive gases are decomposed by it.

SH₂ + Cl₂ = S + 2HCl. Its chief action is as an oxidising agent. Thus
H₂O + Cl₂ = 2HCl + O.

A large excess must be used in disinfecting, otherwise the chlorine
may simply oxidise fœcal or other organic matter, and not effectually
destroy contagia.

_Methods of Use_—(_a_) As a gas, by the action of hydrochloric acid on
strong chloride of lime. The molecular density of chlorine is 35·5, of
formic aldehyde 15, of sulphurous acid 32; and the rate of diffusion of
gases being inversely to the square-root of their densities, clearly
chlorine does not compare favourably as a gas with formic aldehyde.
The bleaching effect of chlorine on coloured articles of apparel is a

(_b_) As a liquid: used thus chlorine is very efficient, applied either
as a spray or brushed on walls and other surfaces. Delépine found
that a solution of one part of chloride of lime in 100 parts of water
applied to wall paper impregnated with tubercular matter, disinfected
it in a few hours, or in a few minutes if the layer of infected matter
was not thick.

=Bromine=, =Iodine=, and =Euchlorine= (a mixture of chlorine and Cl₂O₄)
are efficient disinfectants.

=Iodine Trichloride= (ICl₃) was found by Behring to share with
corrosive sublimate (HgCl₂) carbolic acid and cresol mixed with acids
(see page 327), the halogens (Cl, Br, and I), and chloride of lime a
superiority over other disinfectants in their power of killing anthrax
spores in a short time.

=Permanganates= have been largely used as disinfectants, but their
value is small. Impure sodium manganate (Na₂MnO₄) with much common salt
(NaCl) containing some permanganate is known as “Condy’s Green Fluid.”
“Condy’s Red Fluid” consists of permanganate and sulphate of soda. To
be of any use it must be employed in 5 per cent. solution. It stains
fabrics brown, and it exhausts its feeble disinfecting power in first
oxidising decomposing organic matter.


=Sulphurous Acid= (SO₂) acts chiefly as a reducing agent on organic
matter. It is used chiefly as a gaseous disinfectant, and for this
purpose is generated (_a_) by burning 1 lb. of sulphur for every 1,000
cubic feet of space in the room (which will equal 1·12 per cent.
of SO₂). The windows and chimney of the room are first closed; the
sulphur is placed in a saucepan supported over a bucket of water, and
its ignition is aided by a small quantity of methylated spirit. The
door of the room is then sealed, and the room left until the next
morning. (_b_) Carbon disulphide may be burned in a benzoline lamp.
(_c_) SO₂ liquefied under pressure is supplied in cylinders available
for convenient use. The experimental results of the action of SO₂
on various bacteria are somewhat discrepant. It probably is fairly
efficient for some diseases, but not in tuberculosis.

=Formaldehyde= or Formic Aldehyde (CH₂O) is produced by the slow
and incomplete oxidation of methyl alcohol (CH₃OH) under access of
air. A saturated solution in water containing 40 per cent. of the
formaldehyde gas is known as =formalin=. The simple evaporation or
heating of formalin is liable to produce the polymeric _paraform_ which
is solid and inert. To prevent the formation of paraform when formalin
is evaporated, Trillat adds to it a solution of calcium chloride
(C_a_C_l_₂), the mixture being known as _formochloral_. It is stated
that when the air of a room is charged with less than one per cent. of
the vapour, rapid and complete disinfection of surfaces occurs, and
that it possesses a certain amount of penetrating power into loose
fabrics. No damage is done to textile fabrics; and disinfection by this
means possesses the advantage over disinfection by sulphurous acid
or chlorine that the room can be entered without serious discomfort
soon after the disinfection is carried out. In solution formalin is
undoubtedly a powerful disinfectant, and in the gaseous condition it is
at least equal in value to SO₂, probably better. Formaldehyde is used
as a disinfectant.

(_a_) By evaporating a 60 per cent. solution of CH₂O in methyl alcohol
(trade name _holzine_) over pieces of glowing coke placed under an
asbestos plate (Opperman-Rosenberg apparatus). (_b_) By subliming
tabloids of paraform by the heat of a lamp. A methylated spirit lamp
is employed, and the moisture from the combustion in this causes
the transformation of a considerable proportion of paraform into
CH₂O vapour. It is doubtful if the quantity of the latter evolved
is sufficient for efficiency. (_c_) In Trillat’s apparatus formalin
(_i.e._ the 40 per cent. solution in water of CH₂O) with CaCl₂ solution
is heated in an autoclave worked at a pressure of 40 lbs., provided
with a pressure gauge and thermometer. In all these methods the room
must be carefully sealed, as the tendency for the disinfectant to
escape is greater than with SO₂ or C_l_. (_d_) The best method is to
spray a solution of formalin 4 oz. to one gallon of water on all the
surfaces of the room (see page 333). This is equal to a strength of 1
in 40 of formalin, or 1 in 100 of formic aldehyde.


TAR ACIDS.—When coal tar is treated by acids and alkalies in
succession, it becomes separated into (1) hydrocarbons, (2) phenols
or tar acids, carbolic, cresylic, etc., (3) aniline and other basic
substances. The hydrocarbons are known in commerce as “neutral tar
oils.” They are brown and syrupy, turning milky with water, and feebly
disinfectant. The two most important “tar acids” are phenol or carbolic
acid (C₆H₅OH) and methyl-phenol, also called cresol or cresylic acid
(C₆H₄(CH₃)OH). The higher members of this same group yield milky
emulsions with water, and are less poisonous than phenol. Various
mixtures of them are used as disinfectants, and sold as creolin, Jeye’s
and Lawes’ fluids. Izal belongs to the same series.

=Carbolic Acid= (phenol) did not kill anthrax spores until a 3 per
cent. strength of its solution was used for 7 days (Koch), but
sporeless anthrax bacilli were destroyed in a few minutes by a 1 to 2
per cent. solution. The disinfecting power of carbolic acid is greatly
increased by adding mineral acids. Carbolic acid and lysol are superior
to creolin for disinfecting stools. A 5 per cent. solution of carbolic
acid destroys tubercle bacilli in sputum in 24 hours. _Carbolic acid
powders_ are in common use. In my opinion quicklime is more valuable.

=Cresol= is obtained from “crude carbolic acid” by fractional
distillation at a temperature between 185° and 205° C. A one-half per
cent. solution has equal disinfecting power to a 2 or 3 or sometimes a
5 per cent. of phenol (carbolic acid).

=Creolin= consists of cresol emulsified in a solution of hard soap.
Behring classifies the comparative germicidal power of phenol, cresol,
and creolin on bacteria in broth as 1, 4, and 10 respectively. When
albumen is present, creolin loses a part of its disinfectant power.

=Lysol= contains 50 per cent. of cresol, dissolved by means of neutral
potash soap. It is completely soluble in water and does not turn milky
as creolin does when water is added. It is more effective than creolin,
and still more than HgCl₂ in albuminous liquids.

=Soap= has, owing to its alkalinity, disinfectant as well as cleansing
action. A temperature of 55°-75° C. greatly aids its action.
_Antiseptic soaps_ possess no special value as germicides, but carbolic
soap is a useful insecticide.

=Lime= in a one-tenth per cent. solution destroys typhoid and cholera

=Mercuric Chloride= (HgCl₂, corrosive sublimate) was found by Koch
to destroy anthrax bacilli in a dilution of 1 in 20,000. Others have
obtained less favourable results, but it is certainly a powerful
germicide. The germicidal effect is greatly diminished by contact with
organic matter, an insoluble albuminate of mercury being produced. For
this reason HgCl₂ is not the best disinfectant for fæces unless mixed
with acid, as in the following solution: HgCl₂ ½ oz., HCl 1 oz.,
aniline blue 5 grains to three gallons of water. This gives a solution
of 1 in 960. The colouring is added to avoid accidental poisoning.
HgCl₂ is not a good disinfectant for linen. Stains are apt to be fixed
by it, and if linen soaked in it is subsequently washed with soap,
without first carefully washing out the HgCl₂, it is darkened in
colour. It attacks metals, and must not therefore be placed in metal

=Chloride of Zinc= in a solution containing 25 grains to the fluid
drachm is known as “Sir William Burnett’s solution.” It is a good
deodorant, but an inefficient disinfectant.

=Chinosol= (C₉H₆NKSO₄) belongs to the quinoline group. It is an almost
inodorous powder, very soluble in water, noncorrosive, and does not
stain. A solution of 1 in 1200 forms an efficient germicide.


Natural processes tend to the destruction of pathogenic microbes after
their elimination from the patient. Of these desiccation, sunlight, and
fresh air are the most potent. Heat and cold have a similar effect.
Filtration or mechanical separation deprives a contaminated liquid of
its microbes.

=Desiccation= attenuates the virulence of and finally kills most
microbes. In laboratory experiments the vibrio of Asiatic cholera
when dried dies in from three hours to two days, according to the
degree of desiccation. The bacilli of enteric fever, tuberculosis,
and diphtheria only die after drying for a few weeks or even months.
The anthrax bacillus may retain its vitality for several years in a
desiccated state. Clearly, therefore, desiccation has no administrative
value in the prevention of disease, and on the contrary it aids the
dissemination of the microbes of tuberculosis, small-pox, scarlet
fever, etc.

=Direct Sunlight= kills a large proportion of the sporeless pathogenic
microbes. Diffuse is less energetic in its action than direct sunlight.
The bacillus of diphtheria is destroyed by a half to one hour’s
exposure to sunlight. As to tubercle bacilli, see page 316. Downes
and Blunt showed that diffused sunlight retards the putrefaction of
organic infusions, and that direct sunlight inhibits putrefaction.
Sunlight cannot, however, be trusted as an efficient disinfectant. It
only secures _surface_ disinfection, and could not be relied upon for
pillows, mattresses, etc. M. Ward’s experiments showed that the actinic
rays of the sun are germicidal, independent of the heat.

=Fresh Air=, like sunlight, should be employed as a valuable auxiliary,
not as an agent to be depended upon apart from systematic disinfection.
The experiments of Downes and Blunt showed that light and oxygen
together accomplished what neither alone could do. The presence of
air in anthrax increases danger. The anthrax bacillus does not form
spores in an animal suffering from this disease, and does not do so
_post mortem_, unless the animal is dissected. Hence the importance of
keeping the skin unbroken in this disease, only examining a drop of
blood to establish the diagnosis.

=Filtration= is a means of separating microbes from the gases or
liquids containing them. For the filtration of water see page 96.
The carbolic sheet outside a sick-room is supposed to filter the air
leaving the room from microbes. It is probably useless except as a
reminder to the nurse to change her dress and adopt other precautions
on leaving the sick-room.

=Settlement of dust= also acts as an aerial disinfectant. If a room be
locked up, its air next day is almost free from particles, and all that
is then required is _disinfection of the surfaces_ of the room and of
the articles in it. Whatever method of disinfection is employed, it is
not disinfection of the air, but of the surfaces of a room which is the
end in view.

=Washing= is the most efficacious means of removing infection. It is
a mechanical means of removing the particular matter of which the
contagium consists from the person or article to which it adheres into
the water, which subsequently enters the drain, in the same way as do
urine and fæces. Washing is an absolutely efficient means of purifying
articles that can be completely submitted to it. A consideration of the
=physical laws governing the spread of infection= will make this clear.
The contagia are passive. When contained in a liquid they cannot escape
from it under ordinary circumstances. Thus foul smelling gases may
escape from sewage, but bacteria do not escape, except rarely during
bubbling, or from dried portions of the invert of the sewer. Barring
rare accidents “microbes submerged are imprisoned.” Contagia are
harmless until they become dust. Hence the danger associated with the
use of pocket handkerchiefs in such diseases as influenza and phthisis;
and the importance of keeping all infectious discharges wet, until they
can be finally disposed of.


Heat may be applied in various ways: (1) Prolonged boiling in water of
materials which are not spoilt by this means. (2) Destruction by fire
of infected articles. (3) Dry hot air. (4) Steam.

=Boiling= kills most pathogenic microbes. The cholera vibrio is
killed in four minutes at a temperature of 52° C. (126° F.); the
typhoid bacillus at 59°.4 C. (138°.8 F.) in ten minutes. If boiling
be continued for five minutes, the spores of pathogenic microbes are
killed. The addition of one to two per cent. of washing soda to the
water hastens this effect. For infected linen nothing beyond this is

=Destruction by Fire= is to be recommended for comparatively worthless
articles, such as toys, straw from beds, rags, old clothing and bedding.

=Dry Hot Air= has been largely used in the past in ovens, for the
disinfection of bulky bedding. It is now entirely superseded by steam.
Its disadvantages are that (_a_) heat penetrates very slowly into
the interior of bedding. Disinfection in test experiments was not
accomplished in the interior of small bundles of clothes in three
or four hours. (_b_) Scorching of articles often occurs. The sole
advantage of this method is that bound books and leather goods are
less liable to be damaged by it than by steam. If no other apparatus
is available a baker’s oven will serve to kill the non-sporiferous
microbes of cholera, enteric fever, and diphtheria, as well as animal
vermin. If, however, we accept the proper test proposed by Buchanan of
the efficacy of disinfection, the “destruction of the most stable known
infective matter,” dry heat is unsatisfactory.

=Steam= may be employed as a disinfectant either (_a_) _superheated_,
or (_b_) _saturated_, _i.e._ close to the temperature at which
condensation occurs. This temperature depends upon the pressure under
which the water has been boiled. At ordinary atmospheric pressure
it is 100° C. (212° F.). The temperature of boiling is raised by
subjecting the water to pressure. Consequently boiling water and the
steam produced from it may be at any temperature. Thus steam may be

  (_a_) Under pressure, with a temperature above 212° F.
  (_b_) Not under pressure, at a temperature of 212° F.

[Illustration: FIG. 57.


 =A=—Disinfection chamber. =B=—Partition wall separating infected from
 disinfected side. =C=—Door on disinfected side. =D=—Door on infected
 side. =EE=—Safety-locking bolt for securing door. =FF=—Stiffening
 rings on doors. =G=—Steam inlet from boiler. =H=—Steam separator for
 arresting water condensed in =G=. =I=—Valve controlling admission
 of steam to disinfecting chamber. =K=—Valve controlling admission
 of steam to coils. =LM=—Safety valves regulating steam pressure in
 chamber and coils respectively. =NU=—Pressure guages indicating steam
 pressure in chambers and coils respectively. =OO=—Objects after
 disinfection. =P=—Wheeled carriage and cradle for =OO=. =Q=—Hinged
 rails on which =P= runs. =R=—Exhaust pipe for steam and air on first
 admission. =S=—Thermometer showing rise of temperature (to control
 complete air evacuation). =T=—Valve for closing exhaust pipe =R= when
 air is completely evacuated. =V=—Sluice valve to cause sudden escape
 of steam. =W=—Cock to admit steam to ejector. =X=—Exhaust pipe fitted
 with ejector for escape of steam before and of air during drying.
 =Y=—Valve for admission of air for drying under suction of ejector.
 [In some types of this machine this valve is placed on the lower part
 of =C=.]]

Steam when admitted into a disinfecting stove comes into contact with
cold objects. _If the steam is saturated_, immediate condensation to
1∕1600 part of its original volume occurs. Its latent heat is at the
same time evolved. The condensation causes enormous shrinkage in bulk.
More steam is thus insucked into the partial vacuum produced, and this
is repeated, until in every part of the mattress or other material
undergoing disinfection equality of temperature is reached, when
condensation of steam will cease, and disinfection is complete. _If the
steam is superheated_ and no condensation allowed, disinfection occurs
by the relatively slow method occurring with dry heat. In practice
at the early stage cooling causes some conversion of superheated
into saturated steam, though subsequently the much slower process of
disinfection by conduction of heat goes on. Hence superheated steam is
a less efficient disinfecting agent than saturated steam.

Superheating is produced in disinfecting stores in two ways: (1) By a
jacket around the stove, which is kept at about double the pressure
and about 20° to 30° F. hotter than the interior of the stove; as
in the older patterns of the Washington Lyon stove. (2) By having a
jacket containing a solution of calcium chloride, which is heated by a
furnace under the stove. This solution is kept at a constant strength
by an automatic supply from a cistern. The temperature of the boiling
water is thus raised without pressure to 225° F. This is the principle
of Thresh’s stove. The object of superheating steam is to assist in
rapidly drying materials; but this object can equally well be secured
by periodically allowing the sudden escape of the steam confined under
pressure, in pressure disinfectors. This last method is the best, as
it can not only be utilised at the last stage of the disinfection for
drying the articles; but at the earlier stage for sweeping the air out
of the stove, and thus removing what, owing to its low conductivity
for heat is one of the most serious obstacles to rapid and efficient

In the above description it has been assumed that the steam, whether
saturated or superheated, is =confined=, except when the exhaust is
employed for drying purposes. Steam may also be employed as =current
steam=. Current steam disinfectors are initially cheap, but more steam,
and therefore more fuel, is required in their use; and unless pressure
is used by impeding the escape of the steam a temperature of only 212°
F. can be secured. Accepting Buchanan’s dictum, a stove supplying
saturated steam under pressure at a temperature in the interior of the
stove of 234° F. is to be preferred. This temperature with saturated
steam destroys the spores of the most resistant known microbe (that
of symptomatic anthrax). With superheated steam or hot air stoves on
the same basis a temperature of 280° F. would be required, which is
damaging to most textiles, except horsehair.


The =Management of the Sick-room and Patient= requires careful and
conscientious attention to detail. Certain details are given on page
319. All unnecessary furniture, carpets, and hangings should be removed
as soon as the nature of the illness is known; but unless these
articles have been contained in close trunks or drawers, and not opened
since before the onset of the illness, they must be disinfected. Food
left over from the patient’s meals must be burnt, if solid, in the
patient’s room; if liquid, emptied down the water-closet. Dry sweeping
of the floors is to be avoided, only wet brushing or cloths being used.
Volatile aerial disinfectants during the sickness are valueless.

The =Treatment of Discharges from the Patient= is the most important
point in the management of infection. The stools should be received
into a bed-pan containing a 5 per cent. solution of carbolic acid,
a 3 per cent. solution of cresol or lysol, or a 5 per cent. solution
of chloride of lime. Milk of lime (20 per cent. strength) is very
reliable, when added like the preceding solutions in bulk equal to that
of the stool to be disinfected. The urine and vomit, if any, should
be treated in exactly the same way. The infection of enteric fever is
often spread by undisinfected urine.

Discharges from the =throat, nose and mouth= of patients should be
received into a solution of

  lysol         5 oz. to 1 gallon of water, or
  carbolic acid 7 oz.    „   „         „

The efficacy of the carbolic acid solution is increased by adding 2 oz.
of NaCl, or 12-14 oz. of NaCl to each gallon. Pocket-handkerchiefs must
be avoided, linen rags being employed instead, and placed at once in
one of the above solutions or burnt.

The =skin= may scatter infection, especially in small-pox and scarlet
fever. Frequent baths and inunction with vaseline or oil are useful.

The =disinfection of hands= is most important for all attendants on
the infectious sick. A solution of corrosive sublimate 1-1000, or one
of the above solutions may be used for this purpose; but this is to be
supplemented by the free use of the nail-brush and soap and water. The
treatment of =linen= has been described (page 329).

=Woollen articles= of underclothing, and =blankets= can be disinfected
by steam, which shrinks them less than boiling water. The ordinary
laundry processes appear, however, to suffice to rid them of infection,
without boiling.

=Bedding=, curtains, and carpets should be disinfected by steam.
Certain precautions are required in removing these to the disinfecting
station. Surface disinfection of the room must have been first effected
(see below); and the infected bedding should be encased in canvas bags
or sheets. When a steam disinfector is inaccessible, the mattress
and pillows should be taken to pieces, the covers washed, and their
contents disinfected by spraying with formalin solution (1 in 40) or
HgCl₂ solution (1 in 1,000), and subsequently exposing to sun and air.
For disinfection of suits of clothes, current steam may be improvised
as follows:—Over two bricks at the bottom of the kitchen “copper” thin
floor-boards are placed, above the level of 2 or 3 inches of water
previously placed at the bottom of the copper. The cover of the copper
is put on, and by means of a brisk fire steam is kept streaming through
the clothes. This is continued for an hour, and the clothes then hung
out to dry.

=Furniture=, when wooden, can be washed. If upholstered it can be
disinfected by spraying (see p. 333), and then beating and dusting in
the open air.

=Furs, Boots, and Shoes= are spoilt by steam. For the first, spraying
freely with formalin (1 in 40), or exposure over a formalin lamp (page
326) is recommended. Boots and shoes should be filled and washed with a
solution of HgCl₂, chinosol, or formalin.

[Illustration: FIG. 58.


The =sick-room= can only be efficiently disinfected after the patient
has left it. The aim is _surface disinfection_. Aerial disinfection is
sufficiently effected by open windows. Four chief methods of surface
disinfection are practised. (_a_) _Fumigation_ by SO₂, formalin,
cresol, or other vapours (see page 326). (_b_) _Spraying_ the ceiling,
walls, floor, and furniture with a disinfectant solution is probably
the most convenient method of disinfection. It is more effectual than
fumigation, less laborious than rubbing down walls, etc., by bread
or wet cloth, and less likely to damage wall-papers than brushing
a disinfectant solution on them. Solutions of HgCl₂ 1 in 1,000, or
chinosol 1 in 1,200, or formalin 1 in 40 are efficient. A special spray
apparatus (Fig. 58) is usually employed. A practical point is to spray
the wall from below upwards, to prevent the solution running down the
wall and producing streaks of discolouration. (_c_) _Washing_ ceiling
and walls with the disinfectant solution may be substituted. A one
per cent. solution of hypochlorite of lime is largely used for this
purpose, applied by a long-handled whitewash brush. (_d_) _Attrition_
of walls, etc., by means of bread or dough sterilises them by
mechanically removing microbes. The bread is cut into pieces suitable
for grasping in the hand, the cut surface being applied to the wall.
The crumbs must afterwards be burnt in the room. This is the official
method in Germany.

=Floors= may be treated like walls and ceiling after the patient has
left the room. During his occupancy of the room, tea-leaves or sawdust
thoroughly impregnated with lysol or cresol should be sprinkled on
the floor before it is swept, or washing substituted for sweeping.
Scrubbing with soap and water constitutes the best disinfectant for
floors and all other washable surfaces.

=Books= are difficult of disinfection. Steam damages leather. The
penetrating power of dry heat is doubtful. Cheap books should be burnt.
Abel discovered virulent diphtheria bacilli on toys six months after
the patient, to whom they belonged, had diphtheria. Formalin and phenol
vapours have been used to disinfect books in closed chambers, the books
being stood on end. Letters can be rendered safe by steam disinfection.

=Corpses= of infectious patients should be placed in the coffin and
buried as early as possible. A thick layer of sawdust saturated with
lysol or cresol should be placed at the bottom of the coffin, and the
corpse enveloped in cotton wool. Cremation is better than burial.



Vital Statistics is the science of numbers applied to the life-history
of communities. Its significance is similar to that of the more
recently coined word—Demography—though the latter does not necessarily
confine itself strictly to study of life by statistical means. Another
term has been frequently used in recent years—“Vital and Mortal
Statistics.” The continued use of the word “mortal” in this connection
is undesirable and objectionable. The term “Vital Statistics” is
comprehensive and complete, as death is but the last act of life.

Of the problems of life with which the science of Vital Statistics is
concerned, population, births, marriages, sickness, and deaths, possess
the chief importance; and in the following sketch of the subject
I shall concern myself chiefly with these. The subject naturally
divides itself into two sections: the sources of information, and the
information derived from these sources, and both of these will require

The importance of numerical standards of comparison in science
increases with every increase of knowledge. The value of _experience_,
founded on an accumulation of individual facts, varies greatly
according to the character of the observer. As Dr. Guy has put it:
“The _sometimes_ of the cautious is the _often_ of the sanguine, the
_always_ of the empiric, and the _never_ of the sceptic; while the
numbers 1, 10, 100, and 100,000 have but one meaning for all mankind.”
Hence the importance of an exact numerical statement of facts. The
sneering statement that statistics cannot be made to prove anything can
only be made by one ignorant of science. In fact, nothing can be proved
without their aid, though they may be so ignorantly or unscrupulously
manipulated as to appear to prove what is untrue. Instances of
fallacious use of figures will be given as we proceed.

An accurate statement of =population= forms the natural basis of all
vital statistics. Thus the comparison of the number of deaths in one
with the number of deaths in a second community has no significance
unless we know also the number living out of which these deaths
occurred. Even then our knowledge would be defective, without further
particulars as to the proportion in each population living at different
ages, and the number dying at the corresponding ages. For other
purposes we should require to know the number married and unmarried,
the number engaged in different industries, and so on; in order that
the influence of marital conditions, of occupation, etc., on the
prospects of life may be calculated. The first desideratum of accurate
vital statistics is a =census enumeration= of the population at such
intervals as will not cause the intervening estimates of population
to be very wide of the mark. In this country a decennial census is
taken, the last occurring in 1901. In the intervals the population of
the entire country, and of each town or district is estimated. Various
methods of =estimating the population= have been adopted. (1) If a
strict record of emigration and immigration is kept, then in a country
in which a complete registration of births and deaths is enforced, the
population can be easily ascertained by balancing the natural increase
by excess of births over deaths, and the increase or decrease due
to migration. This is done in New Zealand, but is impracticable in
England, as no complete account of migration can be kept.

(2) The increase of inhabited houses in a district being known year by
year, the increase of population may be estimated on the assumption
that the number of persons per house is the same as at the last census.
This may not be strictly accurate. In 1901 it was found that in England
and Wales the average number of persons per house was fractionally less
than in 1891.

(3) It may be assumed that the annual increase during the present
decennium will be 1∕10 of the increase during the last decennium
1891-1901. If so, the population, _e.g._ in 1905, is the enumerated
population in 1901 _plus_ 4¼ times the annual increase occurring
during 1881-91. (The _fourth_ is required because the census is taken
early in April, and the population is estimated to the middle of the
year). This method is fallacious, because it makes no allowances for
the steadily increasing numbers who year by year attain marriageable
age and become parents. It assumes, in other words, simple interest,
when compound interest is in operation.

(4) The Registrar-General’s method, the one generally adopted, assumes
that the same _rate of increase_ will hold good as in the preceding
intercensal period, _i.e._ that the population increases in geometrical
progression, and not in arithmetical progression as under (3).

The application of this method will be best understood by an example.
If the census population of a town is 32,000 in 1891, and 36,000 in
1901, what is the mean population in 1905?

(_a_) _Find the rate of increase in 1891-1901._

          If P = population at census 1891,
  and if P^{1} =     „           „    1901,
      and if R = rate of increase of population, then
         P^{1} = P - R^{_n_} in the _n_th year.
     log P^{1} = log P + 10 log R.
          1∕10(log P^{1} - log P) = log R.
         (4·556303 - 4·505150)∕10 = ·0051153 = log R.

(_b_) _Apply this to the increase in the next 4¼ years._

  Here P_1905 = P_1901 R^(17∕4)

  log P_1905 = 4·556303 + (17∕4) (·0051153)

  = 4·578043.

 By consulting the table of logs, the population corresponding to this
 number will be found to be 37,848 = population at the middle of 1905.

Estimates made by the last-named “official” method are liable to error,
even for the entire country, and still more when applied to special
districts. Thus the decennial rate of increase of the population of
England and Wales in the 100 years has varied from 15·8 per cent. in
1821-31 to 11·6 per cent. in 1891-1901. The anomalies are even greater
when the official method is applied to great towns. In one decennium
such a town may, owing to brisk trade, have a rapid increase of working
population with many children, and in the next decennium in consequence
of emigration or transmigration there may be little or no increase.
The declining birth-rate, which is having a greater effect on the
number of population than the declining death-rate, is another cause
of disturbance which increases the difficulty in forming a correct
estimate of the population in intercensal periods. A quinquennial
census is highly desirable, in order to avoid the doubts necessarily
associated with estimates of population in the later years of a
decennium, and with the birth and death-rates which are based on these

=The Registration of Births and Deaths.=—Civil registration of births
and deaths began in 1837, but was not compulsory till 1870. It will
be going beyond the scope of this chapter to give details of the
enactments as to registration. It suffices to state that it is the
duty of the practitioner to give a certificate stating the cause of
death of his patient to the best of his knowledge and belief. There
is no registration of still-births in this country. Many deaths are
registered of which the cause of death is not medically certified,
and the value of our national vital statistics is considerably
diminished on this account. Much improvement is desirable in the
medical certification of causes of death. Every medical student ought
to receive instruction on this subject before the completion of
his studies. Names of symptoms as dropsy, hæmorrhage, convulsions;
and obscure names, as abdominal disease, should be avoided. If the
patient has recently suffered from injury, or recently passed through
childbirth, or had a specific febrile disease, this must not be omitted
from the certificate.

=The Registration and Notification of Sickness= forms another valuable
source of information. Various attempts have been made to secure a
general registration of disabling sickness, but with only partial
success. District and workhouse medical officers appointed since
February, 1879, are required to furnish the medical officer of health
with returns of pauper sickness and deaths. This source of information
might with advantage be more fully utilised by medical officers of
health. Sec. 29 of the Factory and Workshops Act, 1895, requires that
every medical practitioner attending on or called in to visit a patient
whom he believes to be suffering from lead, phosphorus, or arsenical
poisoning, or anthrax, contracted in any factory or workshop, shall
send to the Chief Inspector of Factories at the Home Office, London,
a notice stating the name and full postal address of the patient, and
the disease from which he is suffering; a fee of 2s. 6d. being payable
for each notification, and a fine not exceeding 40s. being incurred for
failure to notify.

=The Compulsory Notification of Infectious Diseases= is enforced by
the Act of 1889, which now applies to the whole country. The list of
diseases to be notified is as follows:

 “Small-pox, cholera, diphtheria, membranous croup, erysipelas, the
 disease known as scarlatina or scarlet fever, and the fevers known
 by any of the following names: typhus, typhoid, enteric, relapsing,
 continued, or puerperal, and also any infectious disease to which the
 Act has been applied by the Local Authority in manner provided by the

It is the duty of the medical practitioner to ascertain whether in his
own district, such diseases as whooping cough and measles have been
added to the schedule of notifiable diseases. It is the duty of (_a_)
the head of the family to which the patient belongs; in his default, of
(_b_), the nearest relatives in the house; in their default, of (_c_),
every person in attendance upon the patient; and in default of any such
person, of (_d_) the occupier of the building, as soon as they become
aware that the patient is suffering from an infectious disease to which
this Act applies, to send notice thereof to the Medical Officer of the
District. (_e_) The more formal duty of sending to the Medical Officer
of Health a certificate stating the name of the patient, the situation
of the building, and the infectious disease from which in his opinion
the patient is suffering, is imposed on every medical practitioner
attending on, or called in, to visit the patient, on becoming aware
that the patient is suffering from an infectious disease to which this
Act applies. He is entitled to a fee of 2s. 6d. if the case occurs in
his private practice, and of 1s. if the case occurs in his practice
as medical officer of any public body or institution. He is subject
to a fine not exceeding 40s. if convicted of failure to notify. The
value of returns of infectious diseases as enabling preventive measures
to be taken is increased by interchange of notification returns of
different districts. This is now undertaken weekly for a large number
of districts by the Local Government Board, and the Registrar-General
publishes quarterly summaries of such returns, as well as weekly
returns of infectious diseases for the metropolis.

=Marriages= are usually stated in proportion to the total population,
or the number per thousand of population; but a more accurate method
would be to base the marriage-rate for comparative purposes on the
number of unmarried persons living at marriageable ages. In England the
marriage-rate is always higher in large towns than in rural districts.
Thus in 1900 the marriage-rate in London was 17·6 as compared with an
average marriage-rate in 1891-95 of 15·2 per thousand of the estimated
population in England and Wales. The higher marriage-rate in towns is
chiefly owing to the fact that higher wages and greater scope for
remunerative work attract young country people of marriageable ages to

=Births= are usually reckoned as a rate per thousand of population.
Clearly, however, if one population had a larger proportion than
another of women of child-bearing years this method of comparison
would not be free from possible error. Even were the proportion of
women of child-bearing ages equal, the comparison might be fallacious
if in one population the proportion of single women was much higher
than in the other. Illegitimate births do not materially vitiate this
conclusion, as such births do not constitute more than 4 per cent. of
the total births, and this number is not excessive in the districts in
which there is the greatest excess of single women, viz. in districts
in which a large number of domestic servants are employed. The only
strictly accurate method is to subdivide the births into legitimate
and illegitimate, stating the former per 1,000 married women of
child-bearing years, and the latter per 1,000 unmarried women of
child-bearing years. I append an example of the relative accuracy of
the three methods above indicated[12]:—

  │                     │               BIRTH-RATE               │
  │                     ├──────────────┬────────────┬────────────┤
  │                     │              │            │ PER 1,000  │
  │                     │  PER 1,000   │ PER 1,000  │  MARRIED   │
  │                     │ INHABITANTS. │   WOMEN    │ WOMEN AGED │
  │                     │              │ AGED 15-45.│15-45 YEARS.│
  │ _Kensington_        │   21.8       │      61.6  │  215.4     │
  │ _Whitechapel_       │   39.9       │     172.1  │  328.3     │
  │_Percentage excess   │   83%        │     179%   │   53%      │
  │  of birth-rate in   │              │            │            │
  │ Whitechapel over    │    A         │       B    │    C       │
  │  that in Kensington_│              │            │            │

Thus, according to the ordinary method (A) of stating the legitimate
birth-rate, it is 83% higher in Whitechapel than in Kensington,
whereas it is really only 53% higher. Similarly a statement of the
illegitimate birth-rate in the two districts “per 1,000 inhabitants,”
shows an excess of only 6% in Whitechapel, while a statement “per
1,000 unmarried women aged 15-45 years” shows the real excess of
144%. Both in this and other civilised countries there has been in
the last 25 years a steady decline in the birth-rate. In England the
maximum birth-rate was 36·3 per 1,000 of population in 1876, and the
minimum 29·3 in 1899. This diminution is only caused to a minor degree
by postponement of marriage to more mature years, and by a larger
proportion of celibacy. Nor is there any reasonable ground for the view
that a diminished power of either sex to produce children has been
produced by alcohol, syphilis, tobacco, or other causes. The main cause
of the diminution of the birth-rate is “the deliberate and voluntary
avoidance of child-bearing on, the part of a steadily increasing number
of married persons.”

=Deaths= are calculated in proportion to every 1,000 of the population,
the unit of time being a year. This unit is preserved even when
death-rates for shorter periods, _e.g._ a week, are stated. Thus the
death-rates for the 33 great towns published weekly in the chief
newspapers are _annual death-rates_; they represent the number who
would die per 1,000 of the population, supposing the same proportion
of deaths to population held good throughout the year. The best plan
to obtain the weekly annual death-rate is as follows: the correct
number of weeks in a year being 52·17747, if the population of a town
be 143,956, and the number of deaths in a given week are 35, then the
death-rate is 12·687. Thus:—

  143,956∕52·17747 = 2758. 1,000∕2,758 = 0·3625. This is the factor by
  which the weekly number of deaths must be multiplied.

  35 × 0·3625 = 12·6875 or 12·7.

The above is the _crude death-rate_. Various corrections are required,
which must now be considered. The most important of these are for
public institutions, for visitors, and for age and sex. A public
institution, _e.g._ a workhouse, infirmary, or asylum, in a given
district may consist almost entirely of persons belonging to another
district. The rule is to relegate to the district to which they belong
all deaths of inmates of an institution, _i.e._ subtract all deaths
of outsiders occurring in inside institutions, and add all deaths of
inhabitants occurring in outside institutions. The population as well
as the deaths of these institutions should be excluded, in so far as
they are derived from the outside district, in order to make the net
death-rate approximately correct.

Theoretically the correction ought to be extended so as to apply
to visitors who do not die in public institutions. In practice,
however, this cannot be effected, until a central “clearing house” is
established. The exclusion of deaths of visitors from the district
in which they occur is easy; their inclusion in the returns of the
district from which they come is more difficult to secure. For the
present, they should be included in the death-rate of the district in
which they occur.

=Death-rate according to Age and Sex.=—To obtain a true conception of
the death-rate in a community, it is necessary to state the number of
deaths in each sex in proportion to the number living at different
ages. The importance of this is shown by the following extract from the
Registrar-General’s report for 1899.

England and Wales.—_Deaths to 1,000 living at each of 12 groups of

  │         │  ALL  │ AGED │     │     │     │     │     │      │
  │         │ AGES. │  0─  │  5─ │ 10─ │ 15─ │ 20─ │ 25─ │ 35─  │
  │_Males_  │ 19·5  │ 60·4 │ 3·8 │ 2·2 │ 3·6 │ 5·3 │ 7·1 │ 12·3 │
  │         │       │      │     │     │     │     │     │      │
  │_Females_│ 17·3  │ 50·7 │ 3·9 │ 2·3 │ 3·3 │ 4·3 │ 6·1 │ 10·0 │
  │      │      │      │       │ 85 AND   │
  │  45- │  55- │  65- │  75-  │ UPWARDS. │
  │ 20·0 │ 37·2 │ 69·8 │ 152·6 │  300·3   │
  │      │      │      │       │          │
  │ 15·4 │ 29·8 │ 61·5 │ 142·6 │  272·0   │

Thus at ages over 5 and under 45 for males, and under 55 for females,
the death-rate is lower than is the total death-rate for all ages.
For females at all ages except from 5 to 15, the death-rate is lower
than for males. From the above statement it will be clear that a
considerable excess of women (as in a residential district with a
large number of domestic servants) or a considerable excess of either
sex at the ages of 15 to 45 (as in most large towns) in proportion to
the number living at other ages, would produce a lower total or crude
death-rate, which does not imply any truly more healthy condition than
that of another district, which is less favourably constituted so far
as the proportion of the sexes and the numbers living at different ages
are concerned. By a means of correction now to be described this source
of error can be eliminated. The method of obtaining the _factor for
correction_ can be best understood by an example. The annual death-rate
of England and Wales in 1881-90 was 19.15, and the death-rate at each
age-group is given in the following table:

  │   AGES.         │   MEAN ANNUAL DEATH─RATE   │
  │                 │    IN ENGLAND AND WALES    │
  │                 │1881─90, PER 1,000 LIVING AT│
  │                 │  EACH GROUP OF AGES.       │
  │                 │  _Males._  │   _Females._  │
  │ _Under_ 5       │   61.59    │    51.95      │
  │ 5               │    5·35    │     5·27      │
  │ 10              │    2·96    │     3·11      │
  │ 15              │    4·33    │     4·42      │
  │ 20              │    5·73    │     5·54      │
  │ 25              │    7·78    │     7·41      │
  │ 35              │   12·41    │    10·61      │
  │ 45              │   19·36    │    15·09      │
  │ 55              │   34·69    │    28·45      │
  │ 65              │   70·39    │    60·36      │
  │ 75 _and upwards_│  162.62    │   147.98      │

          │     POPULATION       │     CALCULATED        │
          │       1891.          │   IN HUDDERSFIELD.    │
          │_Males._ │ _Females._ │ _Males._ │ _Females._ │
          │ 4,551   │   4,785    │    280   │    249     │
          │ 4,691   │   5,081    │     25   │     27     │
          │ 5,113   │   5,165    │     15   │     16     │
          ├ 4,905   │   5,549    │     21   │     25     │
          │ 4,541   │   5,461    │     26   │     30     │
          │ 7,466   │   8,834    │     58   │     65     │
          │ 5,576   │   6,265    │     69   │     66     │
          │ 3,944   │   4,649    │     76   │     70     │
          │ 2,393   │   3,017    │     83   │     86     │
          │ 1,128   │   1,590    │     79   │     96     │
          │   250   │     466    │     41   │     69     │
   Totals │44,558      50,862    │    773        799     │
          │     \──────/         │       \───────/       │
          │      95,420          │         1,572         │

The population of Huddersfield at each of the corresponding periods
as given by the census of 1891, is also shown in this table, and in
the last column the number of male and female deaths that would occur
by applying the death-rates for England and Wales to the population
of Huddersfield are shewn. The total number of deaths thus calculated
is 1572 in a population of 95,420, and the total death-rate = 16·47
per 1000. This is the _standard death-rate_, _i.e._, the death-rate
at all ages calculated on the hypothesis that the rates at each of
12 age-periods in Huddersfield were the same as in England and Wales
during the ten years of the last intercensal period, viz. 19·15 in
1881-90.[13] But the standard death-rate of Huddersfield would
have been 19·15 instead of 16·47, were it not for the fact that the
distribution of age and sex in the Huddersfield population is more
favourable than in the country as a whole. Hence it must be increased
in the ratio of 19·15: 16·47, _i.e._, multiplied by the factor
19·15∕16·47 = 1·1627. When the crude or recorded death-rate for 1900 of
16·78 is multiplied by this factor we obtain the _corrected death-rate_
of 16·78 × 1·1627 = 19·51 per 1000, which is the correct figure to
compare with the death-rate of 18.31 for England and Wales in that
year. If the death-rate of England and Wales be stated as 1000, then
1000 × 1951∕1831 = 1066, is the _comparative mortality figure_ for
Huddersfield. Similarly in the year 1900 the comparative mortality
figure of London was 1093, of Croydon 831, of Norwich 919, while
that of Liverpool was 1539, of Salford 1541. In all the towns except
Plymouth and Norwich the corrected death-rate is higher than the crude
or recorded death-rate. This implies that, in all except these two
towns, the factor of correction is greater than unity.

This is a convenient point for briefly discussing the =relationship
between the birth-rate and death-rate=. The opinion is commonly held
that a high birth-rate is a direct cause of a high death-rate, owing to
the great mortality amongst infants. The table on page 340 shows that
the death-rate at ages under five is three times as high as at all ages
together, and it is therefore natural to suppose that a high birth-rate
by producing an excessive proportion of persons of tender years will
cause a high general death-rate. This might be so, if the birth-rate
were to remain high for only five years. But if the high birth-rate
continued longer, the proportion of the total population at ages of
low mortality would be increased, and the general death-rate would
be lowered. We have already seen that in nearly all the great towns,
in which the birth-rate is higher than in rural districts, the age
distribution of the population is more favourable to a low death-rate
than in rural districts; and their higher crude death-rate is made
still higher than that of rural districts when the necessary factor of
correction is applied.

The =Infantile Mortality= should be stated in terms of the infantile
population. This is more accurately assumed to be equal to the number
of births in the given year, than estimated from the number stated to
be under one year of age at the last census. The number of deaths under
one year of age per 1000 births was 163 for England and Wales in 1899,
being lowest in the agricultural counties and highest in manufacturing
counties. In the 33 great towns it averaged 172 in the year 1900,
ranging from 132 in Croydon, Huddersfield and Halifax to 236 per 1000
births in Preston. Of 1000 male children born in England and Wales
in 1881-90, the number surviving at the age of three months was 921,
at the age of six months 889, twelve months 839, while the number of
female children surviving one year of 1000 born was 869. In towns a
smaller number survive. Of the conditions causing this high infantile
mortality, ignorance and inexperience on the part of parents bear a
considerable part, especially as influencing the food and mode of
feeding. The death-rates at other age-groups beyond infancy are given
in the table on page 340. =Season= influences the death-rate. The third
quarter of the year has the lowest death-rate, unless the amount of
Epidemic Diarrhœa has been excessive. In the first quarter of the year,
the highest death-rate usually occurs. Mild winters and cool summers
both lower the mortality. The seasonal incidence of infectious diseases
need only be mentioned in passing.

=Density of Population= has important bearings on the death-rate.
Thus the urban districts in 1899 had a death-rate of 19·2 and the
rural of 16·3 per 1000 of population. Farr found that the death-rate
increased with the density of populations, not in direct proportion,
but in proportion to the 6th roots of the contrasted populations.
This rule does not now hold generally good. It is only after the
density has reached a certain degree of intensity that it begins
to exert an appreciable effect. Even then it is what is implied in
aggregation rather than the aggregation itself that is pernicious. In
particular, poverty is usually greater in densely populated districts
than elsewhere, with its accompaniments of deficient food and clothing
and bad housing. Hence the excess of phthisis in tenemented houses,
especially in houses with only three rooms. I have shown that the true
density that should be considered is the number of persons to each
room, not the number of persons on a given area (“The Vital Statistics
of the Peabody Buildings,” _Roy. Statist. Soc., Feb., 1891_).

=Occupation and Mortality.=—To obtain correct statistics showing the
influence of occupation on vitality, one must know the number and
age of those engaged in each industry, and the corresponding number
of deaths. A statement of the mean age at death of those engaged in
different occupations would be most fallacious (page 344). The best
plan is to restrict the statistics to men aged 25-65, and calculate
for these _death-rates in a standard population_, after the fashion
already described (page 340). By this means a “comparative mortality
figure” can be obtained. For all males it is 1000, for farmers 563,
teachers 603, lawyers 821, doctors 966, butchers 1096, plumbers 1120,
brewers 1427, innkeepers 1659, potters 1706, file-makers 1810. Speaking
generally, the occupations are most unhealthy in which there is most
exposure to dust, to the breathing of foul air, and to excessive
indulgence in alcoholic drinks (for further details see the author’s
_Elements of Vital Statistics_, page 169 _et seq._).

=Deaths from Various Causes.=—These may be stated in proportion to
total deaths from all causes, or in terms of the population. The
first plan must be adopted only when it is desired to ascertain the
proportional share of a given cause of death in the total mortality. In
1899, in England and Wales the diseases named in the first column of
the table (page 344), were the most prolific causes of deaths.



  _Bronchitis_                  880
  _Phthisis_                    729
  _Pneumonia_                   685
  _Old age_                     541
  _Diarrhœa_, _Dysentery_       511
  _Cancer_                      452
  _Apoplexy_                    327
  _Influenza_                   213
  _Whooping cough_              174
  _Measles_                     172
  _Diphtheria_                  160
  _Enteric fever_               108
  _Scarlet fever_                64
  _Small-pox_                     3

The diseases in the second column are given in order to indicate their
proportional share of the total number of deaths.

The proper plan of stating the death-rate from a given disease is in
terms of the population, or better still subdivided into death-rates
from the disease for different age-groups as in the table on page
340, if the number of deaths is not too small to admit of this. The
importance of stating the death-rate for different age-groups is
greatest for such diseases as diarrhœa, whooping cough, and measles,
in which most of the deaths occur at ages under five. In the following
table are given the death-rates from the causes of death which are most
important, either from their magnitude, or because of their preventible


  _Small-pox_                  ·005
  _Measles_                    ·32
  _Scarlet fever_              ·12
  _Influenza_                  ·39
  _Whooping cough_             ·32
  _Diphtheria_                 ·29
  _Enteric fever_              ·20
  _Typhus fever_               ·001
  _Cholera_                    ·04
  _Diarrhœa_, _Dysentery_      ·94
  _Intemperance_               ·09[14]
  _Cancer_                     ·83
  _Phthisis_                  1·34
  _Other tubercular diseases_  ·58
  _Premature birth_            ·58
  _Old age_                    ·99
  _Apoplexy_                   ·60
  _Convulsions_                ·57
  _Valvular disease of heart_  ·38
  _Bronchitis_                1·61
  _Pneumonia_                 1·26
  _Gastro-enteritis_           ·61
  _Bright’s disease_           ·29
  _Accidents_                  ·59
  _Ill defined and not
      specified causes_        ·73
  _All causes_              +18·33+

=Determination of Longevity.= We have hitherto considered only
death-rates, _i.e._ the number dying each year out of each 1,000 of
population. The mean duration of life involves another aspect of the
same problem. Although nothing is more uncertain than the duration
of individual life, the duration of life for the entire community is
subject to so little variation that annuities and life assurance can
be made the subject of exact calculations. Of the tests employed to
measure the duration of human life the most commonly employed is the
=mean age at death=.[15]

                      sum of ages at death.
  Mean age at death = ——————————-——————————-.
                        number of deaths.

This is a fair method of stating the average longevity of a particular
group of persons, if the group is sufficiently large to avoid the
possible error caused by paucity of data (page 349). But it would
be entirely unsafe to assume that by this means a safe standard of
comparison between two groups can be formed. Thus in 1890 it was
stated that the mean age at death of workmen was 29-30 years, of the
well-to-do classes 55-60 years. This statement throws no light on the
relative vitality of the two classes under comparison. The well-to-do
classes consist largely of those whose working days are past; and it
is as untrustworthy to compare their mean age at death with that of
workmen, as it would be to base any conclusion on the fact that mean
age at death of bishops is much higher than that of curates. The mean
age at death is lowest in countries with a high birth-rate. Hence it
would be very fallacious to compare the mean age at death in England
and France.

The =probable duration of life= (_vie probable_) is a term sometimes
employed to denote the age at which any number of children born into
the world will be reduced to one half. In practice it can only be
ascertained from a life-table.

The true mean duration of life or expectation of life can only be
ascertained from a =Life Table=, and this must therefore be briefly
described. This is the true _biometer_, of equal importance in all
inquiries connected with human life with the barometer or thermometer
and similar instruments employed in physical research. The Life Table
represents “a generation of individuals passing through time.” The
data required for its construction are the number and ages of the
living, and the number and ages of the dying, _i.e._ the data required
for ascertaining the death-rate for each year of life. Theoretically
the best plan for forming a Life Table would be to observe a million
children, all born on the same day, through life, entering in a column
(headed _l_{x}_) the number who remain alive at the end of each
successive year until all have died; and in a second column (headed
_d_{x}_) the number dying before the completion of each year of life.
This method is impracticable, and were it otherwise, the experience
would be obsolete before it could be utilised. The method employed in
constructing the national Life Tables for England is, without tracing
the history of individuals through life, to assume that the population
being given by the census returns and the death-rate for each age for
a given decennium being known, that the same death-rate will continue
during the remainder of the lives of the population included in the
census returns.

The total mean number living and the total number dying for a given
age-period are known. The mean chance (_p_{x}_) of living one year
during this age-period is found by the fraction

  Population - ½ Deaths
  ———————————-———————————- = _p_{x}_
  Population + ½ Deaths

It is usual to start with a million or 100,000 children at birth,
and to make a separate table for the proportionate number of males
and females at birth. Thus in Brighton in 1881-90 these were in the
proportion of 51,195 and 48,805. Starting with 51,195 male infants
at birth, and multiplying this number by ·84608, the probability of
surviving for one year, we obtain 51,195 × ·84608 = 43,315. For the
second year of life, the probability of surviving was ·93398; hence the
number of survivors is

 43,315 × ·93398 = 40,452, and so on.

The general arrangement is shewn in the following example of a Life
Table, which only gives the data at or near the two extremes of life,
the intermediate figures having been omitted from considerations of


(Based on the mortality of the 10 years 1881-90.)

  │    │           │    AGE.   │AGE, _x_ + 1, AND   │ LIFE) AT EACH  │
  │    │           │           │UPWARDS, TO THE LAST│  AGE.          │
  │    │           │           │AGE IN THE TABLE.   │                │
  │    │           │           │                    │                │
  │ x  │    d{x}   │    l{x}   │      Σl{x}+1       │      e{x}º     │
  │  0 │   7,880   │  51,195   │      2,206,174     │     43·59      │
  │    │           │           │                    │                │
  │  1 │   2,863   │  43,315   │      2,162,859     │     50·43      │
  │    │           │           │                    │                │
  │  2 │     996   │  40,452   │      2,122,407     │     52·96      │
  │    │           │           │                    │                │
  │  3 │     733   │  39,456   │      2,082,951     │     53·29      │
  │    │           │           │                    │                │
  │  4 │     440   │  38,723   │      2,044,228     │     53·29      │
  │    │           │           │                    │                │
  │ ── │      ──   │     ──    │         ──         │      ──        │
  │    │           │           │                    │                │
  │ ── │      ──   │     ──    │         ──         │      ──        │
  │    │           │           │                    │                │
  │ 97 │      12   │     29    │         43         │      1·60      │
  │    │           │           │                    │                │
  │ 98 │       7   │     17    │         26         │      1·53      │
  │    │           │           │                    │                │
  │ 99 │       4   │     10    │         16         │      1·48      │

The 43,315 males surviving to the end of the first year of life out of
51,195 born will each have lived a complete year in the first year, or
among them 43,315 years. Similarly the 40,452 males will live among
them 40,452 further complete years, and so on, until all the males
started with become extinct at the age of 105. Evidently, therefore,
the total number of complete years lived by the 51,195 males started
with at birth will be

43,315 + 40,452 + 39,456 + 38,723 + ... + 10 + 6 + 4 + 3 + 2 + 1 =
2,206,174 years, this sum being obtained by adding together the numbers
living at each age beyond (_i.e._ below on this table) the age in
question right down to its last item. This number of years is lived by
51,195 males. Hence the number of complete years lived by, _i.e._ the
expectation of life of, each male

  = ————-————- = 43·09 years.

This is the _curtate expectation of life_. It deals only with the
complete years of life, not taking into account that portion of
life-time lived by each person in the year of his death, which may
be assumed to be on an average half a year. Hence the _complete
expectation of life_ according to the above table is 43·59 years.

In the following table the expectation of life (complete) for various
towns and for England is given:—


                                                 _Male._       _Female._
  English Life Table, 1838-54 (_Farr_)            39·91         41·85
     „        „       1871-80 (_Ogle_)            41·35         44·62
     „        „       1881-90 (_Tatham_)          43·66         47·18
  London, 1881-90 (_Murphy_)                      40·66         44·91
  Brighton, 1881-90 (_Newsholme_)                 43·59         49·25
  Manchester City, 1881-90 (_Tatham_)             34·71         38·44
  Glasgow, 1881-90 (_Chambers_)                   35·18         37·70

Formulæ of varying degrees of accuracy have been devised for giving in
the absence of a Life Table an approximation to the expectation of life.

=Willich’s Formula= is as follows:—If _x_ = expectation of life, and
_a_ = present age, then _x_ = 2∕3 (80-_a_). Thus, at the age of 50
years the expectation of life, according to this formula, is 20 years.
By the English life-table for 1881-90 it was 18.82 for males, and 20·56
for females. =Farr’s formula= is based on the birth and death-rates. If
b = birth-rate and d = death-rate per unit of population, then

  Expectation of life = (2∕3 × 1∕d) + (1∕3 × 1∕b).

  Thus b for England and Wales, 1889-98 = 30·3∕1,000 = ·0303.

  and d       „           „       „    = 18·4∕1,000 = ·0184.

(2∕3 × 1∕·0303) + (1∕3 × 1∕·0184) = 47.2 years, as compared with the
expectation of life for 1881-90 shown in the above table.

  In a life-table the number out of which one dies annually}    are
                                      the mean age at death} identical
                                and the expectation of life}  in value

when the whole duration of life from birth to death is included in
the calculation. This is only true for a stationary or life-table
population, in which the number dying is assumed to be regularly
replaced by a corresponding number of persons of the same age.

=Life Capital.=—The life-tables now in use are those based on the
experience of 1881-90. The gain in any subsequent year, as in 1900,
may be ascertained as follows: the mean population and the death-rate
for each age-group as 0-5, 5-10, etc., are calculated. Then the mean
death-rate of the same community for 1881-90 is applied to this
population. By this means the “calculated number” of deaths in 1900 is
obtained. The difference between these numbers and the “actual number”
obtained from the death-registers, gives the gain or loss during the
year. Next multiply these differences by the mean expectation of
life for the corresponding groups of years. By adding the gains thus
ascertained and subtracting any losses, we obtain the net gain in
“life-capital” (Tatham) during the year 1900.

=Tests of the Health of a Community.= 1. The _general death-rate_ is
the test most commonly applied, and generally trusted. It has its
limitations in this respect. It may usually be trusted in comparing a
town or district for a single year with preceding years, as the age
and sex distribution of a given population only changes slowly. But
when comparison with other towns or districts is made, the possibility
that erroneous conclusions may be drawn becomes considerable. (_a_)
Before the death-rates of two districts can be compared, either this
comparison must be made by means of death-rates for age-groups (0-5,
5-10, ... 65-75, etc.) or the factors of correction, the method of
obtaining which is described on page 341, must be applied. (_b_) It
must be ensured that in the two compared districts, an equal amount of
correction has been made for deaths occurring in public institutions
and among visitors (page 340). (_c_) Even when the above precautions
are taken, it is conceivable that a town with a death-rate of 15 per
1,000 may really be as healthy as another with a death-rate of 12
per 1,000, though a statistical justification of this statement is a
difficult task.

Social conditions quite irrespective of the sanitary condition or the
natural salubrity of a district have an important influence on the
death-rate. Poverty and all that it connotes, necessarily involves a
higher death-rate than occurs among the well-to-do. Furthermore, the
domestic servants employed by the latter frequently die in districts
other than those in which they are employed, without any possibility of
the requisite correction being made.

2. _The zymotic death-rate_ is frequently quoted as a test of
sanitary condition. This is a death-rate based on the deaths from the
“seven chief zymotic diseases,” small-pox, measles, whooping-cough,
diphtheria, scarlet fever, fever (chiefly enteric), and diarrhœa. This
death-rate should be entirely discarded, the death-rate from each
infectious disease being separately stated. A high death-rate from
enteric fever would be a much more serious reflection on the health of
a town than a high death-rate for whooping-cough.

The death-rate from each of these diseases in London and in England in
1899 was as follows:—


                        _England and Wales._       _London._

  _Small-pox_                     ·005               _nil_
  _Measles_                       ·32                ·47
  _Scarlet fever_                 ·12                ·08
  _Diphtheria_                    ·29                ·43
  _Typhus_                        ·001               _nil_
  _Enteric fever_                 ·20                ·18
  _Whooping cough_                ·32                ·38
  _Diarrhœa_                      ·94                ·92

A statement of the death-rate from each of these diseases for a series
of years is a much more trustworthy test than a similar statement for
a single year, in which accidental causes may have caused a temporary
increase, or than a statement of the average result for a series of
years, which tends to conceal the epidemic variations of the disease
in question. The danger of such averages has been well exposed by
Chadwick in the remark that “a mean between the condition of Dives and
Lazarus tends to make it appear that after all Lazarus has not so much
to complain of.”

3. _The infantile mortality_ (page 342) is a delicate test of mixed
sanitary and social conditions, and stress may always be laid on it
from these standpoints. The importance of comparing death-rates at
other age-groups has already been explained.

4. The most delicate and exact method, if all the data are accurate and
complete, is to construct a _Life Table_, and ascertain the expectation
of life in comparison with that of other communities.

The preceding statistical tests of the salubrity of a community,
and any others that may be available, should all, when practicable,
be utilised; and it should always be remembered that these tests,
especially the general death-rate, are most trustworthy when
contrasting the experience of a community with its past experience, and
least trustworthy when contrasting its experience with that of others;
owing to the difficulty in the latter case of ensuring the avoidance of
error arising from _non ceteris paribus_.

=Statistical Fallacies.=—If “fallacies” be regarded as synonymous with
“errors,” clearly they may occur at every step. They may be classified
as errors of data, and errors of methods. The most important _errors
of data_ are erroneous estimates of population, and erroneous returns
of deaths, especially in the direction of exclusion of certain deaths
(page 340). Death-rates for short periods are relatively untrustworthy.
The erroneous use of the mean age at death as a test of longevity has
been mentioned (page 344). These are in part also _errors of methods_,
and numerous mixed examples are given below.

=Errors from Paucity of Data= frequently arise, the “fallacy of
small numbers,” a too hasty generalization, being the most common
fault in medical writings, especially in therapeutics. The degree of
approximation to the truth of a varying number of observations is
estimated by means of =Poisson’s formula=.

  μ = total number of cases recorded in two groups.
  m = number in one group.
  n = number in the other group, so that μ = m + n.

The extent of variation in the proportion of each group to the whole
will vary within the proportions represented by—

  m∕μ + 2√(2mn∕μ^3), and n∕μ - 2√(2mn∕μ^3)

The larger the number of the total observations (μ), the less will be
the value of 2√(2mn∕μ^3), and the less will be the limits of error in
the simple proportion m∕μ.

Thus, of 147 cases of enteric fever, 17 died, a fatality of 11·4 per
cent. The possible error is determined by the second half of the above

  = 2√(2 × 17 × 130∕147^3) = 2√(4,420∕3,176,523) = ·0746.

_i.e._ the possibility of error = ·0746 to unity or 7·46 per cent. In
other words, in a second series of cases of enteric fever under the
same conditions as the above, the fatality may vary from 3·94 to 18·86
per cent., a vague result which indicates that the first series cannot
be regarded as establishing more than a _primá facie_ case in favour of
any special method of treatment that may have been adopted.

=Non ceteris paribus.=—The necessity that data to be compared shall be
collected on a uniform plan, and be of a strictly comparable nature,
is very frequently ignored. The conclusion that the administration of
a given antiseptic is a valuable means of treating enteric fever is
not demonstrated by the fact that the fatality in the series of cases
thus treated is 7 per cent., while in another series treated without
antiseptics it is 14 per cent., unless it is shown that the age and
other previous conditions of the patients in the two cases were not
widely different, and unless the series are sufficiently long to avoid
the fallacy due to paucity of data.

=Errors from the Composition of Rates.=—If the death-rate of A having
a population of 10,000 is 10 per 1000, and of B having a population
of 20,000 is 15 per 1000, the combined death-rate is not (10 + 15)∕2
= 12·5. To obtain the correct combined death-rate, the number of
deaths in A (=100) and in B (=300) must first be ascertained, and the
death-rate on a population of 30,000 in which 400 deaths occurred will
then be found to be _13·3 per 1000_.

=Errors from Stating Deaths in proportion to Total Deaths.=—There is
nothing erroneous _per se_ in stating the proportion of deaths at one
age as a ratio of the total deaths at all ages, or the deaths from one
cause as a ratio of the total deaths from all causes. It is a useful
and in fact the only method practicable when it is required to give the
proportion of one of these to the other. But beyond this, such a ratio
cannot be trusted. For instance, the proportion of fatal accidents
among male infants is 12·2, and among female infants 25·1 per cent. of
the total fatal accidents in the male and female sex respectively. But
it would be erroneous, if it were concluded from these figures that
female are more subject to fatal accidents than male infants. The only
conclusion that they justify is that at higher ages females are much
less subject to fatal accidents than males. In actual facts, for every
1000 infants born, only 2·9 female as against 3·1 males die under one
year of age as the result of accident.

Again, suppose the case of two towns, A and B. A with a population
of 10,000 has 150 annual deaths, of which 20 are caused by cancer;
the general death-rate therefore being 15, and the death-rate from
cancer 2·0 per 1000, while the deaths from cancer form 2∕15 of the
total deaths. B, with the same population as A, has 300 deaths, its
death-rate being 30 per 1000, and 40 deaths from cancer, its cancer
death-rate being 4·0 per 1000; while the proportion of the deaths from
cancer to the total deaths is 2∕15 as before. It is useful to know
in regard to each of these individual communities that cancer causes
2∕15 of its total mortality, but no comparison between the two is
practicable on this basis. The only proper comparison is between the
death-rate from cancer per 1000 of population in A and B, which shows
that it is twice as high in B as in A. A still more accurate method is
to ascertain the number of deaths from cancer, and the number living at
different age-groups, thus avoiding any errors due to variations in age
and sex distribution of population.

=Errors as to Averages.=—The most common of these results from
paucity of data (page 349). Note that the results obtained from an
average cannot be applied to a particular case. The mean duration or
expectation of life, obtained from a life-table, expresses with almost
mathematical certainty, the number of years of life of the members of
a community _taken one with another_, but is often not accurate when
applied to a single individual.

In _Army statistics_ errors have arisen by failure to comprehend what
is meant by the _average strength_ of a force. The statistics must
comprise the lives of a given number of persons as well as the deaths
occurring among them _for an entire year_, or allowance must be made in
this respect when required.

_Hospital statistics_ for similar reasons are frequently fallacious.
Thus death-rates have been frequently given per 100 occupied beds,
which are most misleading, as the frequency of succession of patients
as well as the nature of the patients’ complaints will vary greatly in
different hospitals. The only proper method of stating hospital-returns
is on the basis of the aggregate annual number of cases treated to a
termination. The cases should be further subdivided according to age
and sex and disease. _Average death-rates for epidemic diseases_ when
used to compare one community with another may give rise to erroneous
conclusions. This is inseparable from the nature of such diseases.
During the period under comparison, one town may happen to have,
say, three epidemics, and the other four; possibly if two or three
additional years had been added to the series, the place of the two
towns would have been reversed as regards their average death-rate from
the disease in question. The proper plan is to give the death-rates
from the epidemic disease for every year recorded, to draw a curve of
these death-rates for the two towns on the same scale, and to compare
the height, the variations of height, and the trend of the curve in
each instance.



  Acarus Scabiei, 276

  Achorion Schönleinii, 276

  Acne, 161

  Aerated Waters, 46

  Ague (see Malaria)

  Air—Bacteria in, 109, 121
    Composition, Properties of, 100
    Contagia and, 109, 114
    Degree of Moisture of, 119, 128
    Gaseous and Other Impurities of, 111
    Examination of, 126
    Moisture of, 234
    In Soil, 221
    Suspended Impurities of, 105
    Temperature of, 119, 128
    of Mountains, 228
    Purification of, 129

  Air-space, amount required, 142

  Alcohol, 55

  Amines process, 191

  Ammonia—in Air, 101
    in Water, 86

  Amyloids, 7

  Amylaceous Foods, 19

  Anopheles (see Mosquito)

  Anthrax, 274, 306

  Anti-cyclones, 233

  Antidiphtheritic Serum, 268, 299

  Anti-syphonage, 174

  Antill Trap, 180

  Apjohn’s Formula, 242

  Arnott’s Valve, 149

  Arrowroot, 19

  Arsenic—in Beer, 62
    in Wall Papers, 214
    in Clothing, 272

  Artesian Wells, 71

  Artificial Ventilation, 152
    Relative Value, 154

  Ascaris, 278

  Ash-pits, 199

  Aspect, 201

  Atavism, 246


  Bacteria, 273

  Bacterial Methods, Sewage Treatment, 192

  Ballard’s Researches, 303

  Barley, 18

  Barometers, 237

  Barometric Pressure, 231

  Baths, 262

  Beaufort’s Scale, 243

  Beef, 10

  Beer, 61

  Bell-trap, 180

  Benham’s Gas Burners, 157

  Berkefeld Filter, 98

  Beverages, 46

  Bilharzia Hæmatobia, 277

  Birds, Flesh of, 11

  Birth-rate, 339

  Black Death, 1

  Bonds, English, Flemish, 205

  Borax and Boric Acid, 44

  Boyle’s Mica Valve, 149

  Bowels, Attention to, 248

  Brandy, 63

  Bread, brown and white, 17, 41

  Bricks, 205

  Broad Irrigation, 192

  Burnett’s Solution, 327

  Butter, 14

  Buys Ballot’s Law, 232


  Caffeine, 48

  Calorigen Stove, 157

  Carbohydrates, 6

  Carbolic Acid as Disinfectant, 327

  Carbon Filters, 97

  Carbonic Acid—in Air, 102, 111
    estimation of, 126

  Carbonic Oxide, 112

  Calorie, 32

  Carpets, 218

  Cement, 213

  Cereal Foods, 15

  Cesspools, 183

  Cheese, 13

  Chicory, 50

  Chigoe, 277

  Chlorides in Water, 81

  Chlorine as Disinfectant, 324

  Cholera, 92, 225, 302

  Cisterns, 76

  Clarke’s Process, 94
    Soap Test, 79

  Climate, 227

  Closets, 168

  Clothing, 265

  Coal Gas, 115

  Cocoa, 51

  Cod Liver Oil, 14

  Coffee, 50

  Cols, 233

  Comparative Mortality Figures, 342

  Concrete, 207

  Condiments, 45

  Condy’s Fluid, 325

  Conservancy Methods, 194

  Constipation, 248

  Constitution, 245

  Consumption (see Tuberculosis)

  Container, 169

  Cooking, 339

  Cooper’s Ventilators, 149

  Corrosive Sublimate as Disinfectant, 327

  Cotton, 270

  Cream, 15

  Cyclones, 232

  Cysticercus Cellulosæ, 23, 279


  D-Trap, 169

  Damp, Cause of, 211

  Damp-proof Course, 210

  Death-rate, 2
    Crude, 340
    Corrected, 342
    Zymotic, 297, 348

  Decomposed Meat, 24

  Demography, 335

  Density of Population, 343

  Destructors, 200

  Dew Point, 241

  Diarrhœa, Epidemic, 302

  Diet, 29

  Dietaries, 33

  Diffusion, 129

  Diphtheria, 225, 298

  Diseased Animals, Meat of, 23

  Disinfection, 324

  Distillation, 94

  Drainage, 166
    of Soil, 226

  Drains, 177
    Examination of, 180

  Drugs, 54

  Dust in Air, 105

  Dust-bins, 199

  Dyspepsia, 28, 248


  Earth-closets, 195

  Eggs, 11

  Ellison’s Bricks, 151

  Endemic Diseases, 289

  Enteric Fever, 91, 224, 300

  Epidemic Diarrhœa, 26, 225, 302

  Epidemic Diseases, 289

  Erysipelas, 110, 305

  Excreta, 165

  Exercise, 249

  Expectation of Life, 346


  Farcy (see Glanders)

  Farr’s Formula, 347

  Fats, 6

  Favus, 276

  Fermented Drinks, 55

  Filaria, 278

  Filters, 97

  Filtration, 95

  Fire Grates, 159

  Fish, 11
    Dangers of, 26

  Flax, 270

  Fleas, 277

  Flesh Food, 9

  Floors, 217

  Flour, 16

  Flukes (see Trematoda)

  Fomites, 299

  Food, 4
    Diseases due to, 23
    Heat value of, 32
    Preparation and Preservation of, 38, 43
    Relation of, to Mechanical Work, 36
    Variations from Climate, Age, &c, 29
    Vegetable and Animal, 31

  Forests and Climate, 229

  Formalin., 44
    and Formaldehyde as disinfectants, 326

  Fortin’s Barometer, 238

  Fruits, 21

  Fuel, 161

  Fungi, 20


  Gaertner’s Bacillus, 25

  Galton’s Stove, 155

  Gas Stoves, 157, 161

  Gelatin, 9

  Gin, 63

  Glanders, 304

  Glaisher’s Tables, 241

  Glucose, 21

  Gluten, 15

  Gout, 28, 59

  Goux System, 194

  Graveyards, Air of, 118

  Green Vegetables, 20, 42

  Ground-water, 222

  Gully-trap, 167, 180


  Habits, 247

  Haffkine’s Cholera Vaccine, 228

  Hardness of Water, 79, 90

  Heat, kinds of, 159

  Hendon Disease, 27

  Heredity, 245

  Hermite Process, 191

  Hopper-closets, 170

  Hot Water Supplies, 163
    Pipes, 162

  House Construction, 209
    Drainage, 165
    Materials of Construction of, 205
    Position of, 201
    Refuse, 198
    Slops, 165

  Humidity, absolute and relative 235
    Measurement of, 240

  Hydatids, 279

  Hydrocarbons, 6

  Hydrophobia, 305

  Hygrometers, 101, 240


  Idiosyncrasy, 246

  Illuminants, 115

  Immunity, 287

  Incubation Periods, 287

  Infantile Mortality, 342

  Infective Diseases, 284
    of Animals, 24

  Infectious Diseases, Hospitals for, 320
    Notification of, 338

  Influenza, 309

  Insects and Disease, 281

  Intermittent Downward Filtration, 192

  Iron in Water, 83

  Isobars, 231

  Isolation, 319

  Isothermal Lines, 230


  Jenner’s Discoveries, 293


  Koch’s Postulates, 285


  Latrines, 174

  Laveran, 282

  Lead in Water, 82, 90
    Workers in, 108

  Lice (see Pediculi)

  Liebig’s Extract of Meat, 10

  Life Capital, 347
    Tables, 345

  Linen, 270

  Lysol as Disinfectant, 327


  Macaroni, 17

  Main Sewers, 183

  Maize, 18

  Malaria, 91, 224, 307

  Mallein, 304

  Malt, 18, 62

  Malted Bread, 17

  Margarine, 15

  McKinnell’s Ventilator, 149

  Metabolism, 6

  Measles, 297

  Meat, 9
    Diseased, 24
    Tinned, 25
    Parasites in, 23

  Meat Poisoning, 25

  Metchnikoff’s Theory, 289

  Meteorological Observations, 237

  Metallo-keramic Joint, 177

  Miasm, 285

  Microbes (see Bacteria)

  Microscoporon Audouini, 275

  Milk, 12
    and Disease, 26, 296, 299, 301
    Boric Acid in, 44
    Souring of, 274
    and Tuberculosis, 311

  Mineral Waters, 47

  Mortar, 206

  Mosquito, 282, 308

  Moule’s Closet, 195

  Mountain Climate, 228

  Mutton, 10


  Natural Ventilation, 147
    Relative value, 154

  Nematoda, 278

  Nitrogen, 274

  Nitrates in Water, 81

  Nitrification, 192, 220

  Nitrogenous Foods, 5

  Notification of Consumption, 314
    Infectious Diseases, 318, 338
    Trade Diseases, 337


  Oatmeal, 17

  Obesity, 28

  Occupation and Mortality, 343

  Offensive Trades, 120

  Oidium albicans, 275

  Oils, 46

  Onion, 20

  Over-feeding, 28

  Oxygen in Air, 100

  Oxygen Absorbed, 86

  Oxyuris, 278

  Oysters and Disease, 291

  Ozone, 101


  Pan-closets, 169

  Pandemics, 289

  Parasites, 276
    in Meat, 23

  Pasteur-Chamberland Filter, 98

  Pasteurization of Milk, 13, 312

  Pediculi, 277

  Personal Hygiene, 245, 257, 260

  Pettenkofer’s Method, 126

  Phagocytosis, 287

  Phosphorus, in Food, 5
    Workers with, 108

  Phthisis, 225, 310

  Piles, 248

  Plaster, 212

  Plague, 281, 305

  Pneumatic System, Liernur, 183

  Poisson’s Formula, 349

  Population, Density of, 343
    Estimation of, 336

  Pork, 11

  Porter-Clarke Process, 95

  Portland Cement, 206

  Potato, 20

  Privy or Midden System, 196

  Proof Spirit, 64

  Proteids, 5

  Propulsion, Ventilation by, 153

  Puerperal Fever, 306


  Quarantine, 320


  Rabies (see Hydrophobia)

  Rainfall, 235

  Rain Gauge, 242
    Water, 67
      Pipes, 166

  Rats and Plague, 306

  Registration of Births and Deaths, 337

  Relapsing Fever, 28, 300

  Respiration, 102, 113

  Rest, 257

  Rheumatic Fever, 225, 306

  Rickets, 28

  Ringworm, 275

  Rivers, 72

  Roasting, 38

  Roofs, 208

  Rum, 63

  Rye, 18


  Saccharomycetes, 275

  Sago, 19

  Salts as Food, 7

  Saprophytes, 286

  Scarlatina or Scarlet Fever, 296

  Schools, Closure of, 322

  Scott Moncrieff Process, 192

  Scrofula, 316

  Scurvy, 2, 27

  Seasonal Incidence of Diseases, 289

  Sea Relation to Climate, 229

  Sebaceous Glands, 260

  Semolina, 17

  Septic-tank, 193

  Sewage—Disposal of, 190
    Dry and Wet Methods of Removal of, 197

  Sewers, 183, 184
    Air of, 117
    Problems as to flow in, 187

  Shell-fish and Disease, 291

  Sheringham’s Valve, 151

  Shone System, 186

  Sinks, 167

  Silk, 270

  Sleep, 258

  Slop-closets, 174

  Small-pox, 2, 292

  Smoke Nuisance, 160
    Test, 181

  Soap, 261

  Soil, 219
    Diseases in Relation to, 224
    Drainage of, 226

  Soil-pipe, 174

  Spices, 46

  Spirits, 63

  Springs, 68

  Starch, Detection of, 19

  Starvation, 27

  Statistical Fallacies, 349

  Steam as Disinfectant, 329

  Stoves, 157, 161

  Streets, Width of, 203

  Sugar, 21

  Sulphuretted Hydrogen, 112

  Sulphurous Acid (Disinfectant), 325

  Summer Diarrhœa, 225

  Sunshine Recorders, 243

  Sweat Glands, 260

  Sweating Sickness, 1

  Sylvester’s Method, 150

  Synoptic Map, 231

  Syphonic Closet, 172


  Tannin, 49

  Tape-worms, 279

  Tapioca, 19

  Tea, 30, 47

  Temperature of Rooms, 158

  Tetanus, 304

  Thermometers, Maximum and Minimum, 239

  Thermometers, Dry and Wet Bulb, 240

  Thrush, 275

  Tight Lacing, 267

  Tinea, 276

  Tobacco, 54

  Tobin’s Tubes, 152

  Toxins, 286

  Trades and Disease, 107, 118
    Offensive, 120

  Traps, 179

  Trematoda, 277

  Trichina Spiralis, 23

  Trichophyton, 275

  Trough-closets, 174

  Tuberculin Test, 311

  Tuberculosis, 309
    Prevention of, 314

  Tuberculous Meat, 24

  Typhoid Fever (see Enteric Fever)

  Typhus Fever, 300


  V-shaped Depressions, 233

  Vaccination, 293

  Valve-closets, 170

  Variola (see Small-pox)

  Veal, 10

  Vegetables, 20

  Ventilation, 132
    Methods of, 146
    Problems as to, 137
    By Propulsion, 153

  Ventilation by Introduction of Warmed Air, 155
    Of Mines, 156
    Of Drains, 178

  Vermicelli, 17

  Vernier, 238

  Vinegar, 46

  Vital Statistics, 335


  Wall-paper, 214

  Walls of House, 210

  Wanklyn’s Ammonia Process, 86

  Warming of Houses, 159

  Wash-out and Wash-down Closets, 172

  Waste-pipes, 166

  Water, 65
    As food, 8
    Analysis of, 84
    Classification of supplies of, 73
    Constant and Intermittent Services, 76
    Enteric Fever and, 72
    Hardness of, 79
    Impurities of, 78, 89, 90
    Sources of, 66
    Storage and Delivery of, 74
    in Soil, 222
    Purification of, 94

  Water-closets, 168

  Water-gas, Carburetted, 115

  Water-test of Drains, 182

  Weather Forecasting, 234

  Weissman on Heredity, 246

  Wells, 69

  Whiskey, 63

  Whooping Cough, 298

  Widal Reaction, 301

  Willich’s Formula, 347

  Windows, 216

  Winds, 131, 230, 243

  Wines, 62

  Wool, 269

  Wool-sorters’ Disease, 274

  Work, Amount done, 252
    Relation of Food to, 36

  Wort, 62

  Writers’ Palsy, 252


  Yellow Fever, 305


  Zygophyta, 275


[Footnote 1: While the addition of animal fat like margarine raises the
melting point, rape-seed oil and other vegetable oils lower it.]

[Footnote 2: The fat to be analysed is saponified with soda or potash,
and then the fatty acid set free by hydrochloric acid. If water be now
added, 11 or 12 per cent. of the fatty acid will be dissolved, if the
fat is butter; less than this if it is a mixture; and not more than 5
per cent. if no butter is present in the fat.]

[Footnote 3: Freshly made; of which 1 c.c. = ·00001 grm. of N₂O₃]

[Footnote 4: Made by dissolving ·395 grm. of KMnO₄ in 1,000 c.c. of
water. Each c.c. of this solution =·0001 grm. of oxygen available for

[Footnote 5: Caused by the liberation of iodine. Thus—

 K₂Mn₂O₈ + 8 H₂SO₄ + 10 KI = 6 K₂SO₄ + 2 MnSO₄ + 8 H₂O + 5 I₂.]

[Footnote 6: Of the strength of 1 grm. of crystalline sodium
thiosulphate to 1 litre of water.]

[Footnote 7: In practice one has frequently to be contented if the CO₂
does not exceed 1 part per 1000 of air; and if the room is clean and
free from dust, this higher limit may be accepted.]

[Footnote 8: The damp-proof course should have been shown close under
the plate carrying the floor joists.]

[Footnote 9: Some bacteria form in their interior minute _spores_, by
means of which they are able to resist ordinary destructive agents.
These spores again develope into bacteria.]

[Footnote 10: Furthermore, it is stated that when at rest on a plane
surface the Culex assumes a position with the axis of the body more
or less parallel to the surface; while the Anopheles, under the same
circumstances, has the axis of its body more or less at right angles to
the surface.]

[Footnote 11: This is diphtheria attacking the larynx]

[Footnote 12: From “Elements of Vital Statistics,” by A Newsholme.]

[Footnote 13: This was written before the figures for the period
1891-1900 were available; but the method adopted is the same,
substituting the death-rates, etc., for the later period.]

[Footnote 14: The death-returns greatly understate the actual
death-rate from this cause.]

[Footnote 15: There is no general agreement as to the exact sense in
which the words _average_ and _mean_ should be used. They are used here

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