for the most part derived from the human body, chiefly from
respiration, and these only will be considered here. In some cases it
is necessary to make special provision for the products of combustion
from gas, etc., but as a rule this is rather for the purpose of
regulation of temperature than anything else. The impurities of air
due to the presence of human beings consist mainly of carbonic acid,
ammonia, sulphuretted hydrogen, and sulphide of ammonium, and of
various organic compounds, mostly in the form of minute particles of
organic matter of uncertain structure, but extremely prone to
decomposition. It is usual to estimate the degree of impurity by the
amount of carbonic acid present, and this leads many persons to
suppose that the carbonic acid is in itself the chief and most
dangerous impurity. This gas is, however, not perceptible to the
senses, {178} nor is it injurious to health, unless present in much
greater proportion than that in which it will be found in the most
crowded habitations or assembly-rooms. Its importance in questions of
ventilation depends upon the fact that its increase in a room beyond
the amount present in the outer air may usually be taken to be in
direct proportion to the amount of the really dangerous and offensive
impurities present, and that the amount of carbonic acid can be
ascertained by chemical tests with comparative ease and rapidity;
which is not the case with regard to the organic matter. The carbonic
acid is therefore taken as the measure of the impurity, although it is
not itself the impurity of which we are most anxious to be free.
To decide as to whether a room is well ventilated or not, some
standard of permissible impurity must be fixed, and this standard is
now usually taken to be, in a room occupied by human beings, that
condition of air which produces in a person having a normal sense of
smell, and who enters from the fresh air, a faint sensation of an odor
very slightly musty and unpleasant. Upon testing the air of such a
room, it will be found that the amount of carbonic acid impurity
present--that is, the excess of this acid over the amount in the
external air--will be between 2 and 3 parts in 10,000.
As the amount of carbonic acid in normal air varies from 2 to 5 parts
in 10,000 in different places, and in the same place at different
times, it is better to look to the carbonic acid impurity as above
defined rather than to the total amount of the acid found present, if
strict accuracy is desired; but usually the statement of Dr. Parkes is
correct, that the organic impurity of the air is not perceptible to
the senses until the total carbonic acid rises to the proportion of 6
parts in 10,000 volumes. When the carbonic acid reaches 9 parts in
10,000 the air is close, and when it exceeds 1 part in 1000 the air is
usually decidedly unpleasant. If we take 2 parts in 10,000 as the
permissible maximum of carbonic acid impurity, it follows that the
amount of fresh air which must be supplied and thoroughly distributed
for each person per hour is 3000 cubic feet. If 3 parts per 10,000 be
taken as the permissible maximum (which is the standard of
Pettenkofer), the amount of air per head per hour must be 2000 cubic
feet. While it is impossible, as Dr. Parkes remarks, to show by direct
evidence that the impurity indicated by 7, 8, or even 10, parts of
carbonic acid per 10,000 is injurious to health, it is advisable to
accept his standard, because it is a simple one, and can be
practically applied without special apparatus or technical skill, and
because there is evidence of the injury to health which continued
exposure to air impure, by this standard, ultimately produces.
Keeping this standard in view, the physician may be called on for an
opinion as to whether the ventilation of a given building is
satisfactory or as to the merits of a proposed plan for ventilation.
The first is a question of fact: What are the effects produced upon
the inmates? Are there unpleasant odors in the building or not? What
percentage of carbonic impurity is present? What is the number of
cubic feet of air per head that is introduced and removed per hour?
And what is the character of the fresh-air supply as to purity? Does
it come from the cellar, or from other rooms, or from a foul area?
Air-currents can usually be best investigated by the fumes of nascent
muriate of ammonia produced by {179} exposing a cylinder of common
blotting-paper, moistened with dilute hydrochloric acid, to the vapors
coming from a crumpled fragment of the same paper moistened with
common aqua ammonia and placed within the cylinder. The process for
carbonic acid determination is simple, and can be learned in three
hours in a laboratory under a skilful teacher. It does not seem worth
while to describe it here. The determination of the amount of air
passing through a given register, flue, or chimney in a given time is
to be made by the use of an anemometer, an instrument which registers
the velocity of the current of air passing through it.
In judging of the merits of a plan of ventilation the following points
should be remembered: The defect in most plans for ventilation is in
the air-supply. Many people suppose that they have made all necessary
provision for ventilation if they have put in tubes or openings for
the escape of foul air, forgetting that these outlets will have no
effect if corresponding inlets are not provided. Examine, first of
all, therefore, the ducts, flues, and openings proposed for the
fresh-air supply, with reference to their size and position and the
amount of air to be furnished by them. These will almost invariably be
found to be too small. The proper size of flues and registers for a
given room is ascertained by dividing the number of cubic feet of air
to be supplied per second by the velocity in feet per second which the
air is to have in the flue or opening, bearing in mind that it is much
better that these flues and registers shall be too large than too
small, since it is easy to reduce their capacity, but, in most cases,
impossible to increase it. When the fresh-air register is so situated
that the current of air from it is liable to strike upon the person of
an occupant of the room, the velocity of this current should not
exceed 1-1/2 feet per second if unpleasant draughts are to be avoided;
and it will usually be found best that the velocity of the air in the
flue shall not exceed 6 feet per second, except in the case of very
large flues, where the element of friction becomes of comparatively
small importance. In the great majority of cases the amount of air to
be supplied depends upon the number of persons, and not on the cubic
space; but in exceptional instances, where the amount of cubic space
is very large in proportion to the number of persons, and the heating
is effected by warm air, it may require more air to keep the room at a
comfortable temperature than is necessary for the supply of the
occupants. The cubic space is also relatively much more important in
rooms which are to be occupied but a short time continuously, and can
then be thoroughly aired, than it is in rooms constantly occupied.
The methods of calculation can be best illustrated by one or two
examples. What should be the number and size of flues and registers
for fresh-air supply for a hospital ward to contain 24 beds, the ward
being a rectangular pavilion with windows on opposite sides? In this
case the room is constantly occupied, and the supply of air should be
1 cubic foot per head per second, or, in all, 24 cubic feet per
second. The velocity of current at the registers should not exceed 3
feet per second--better only 2. This will require from 8 to 12 square
feet of clear opening in the registers. If we allow four on each side
of the room, each register must have at least 1 square foot of clear
opening. The velocity of the air in the flues supplying these
registers should not exceed 4 feet per second, and therefore the area
of each flue should be about 9 by 12 {180} inches. Suppose the same
question be asked with regard to a school-room to contain 48 pupils.
In this case the room will not be occupied more than two hours at a
time. The air-supply desirable may be put down at 35 cubic feet per
head per minute, or 28 cubic feet per second for the whole. The
velocity in the flues may be put, as before, at 4 feet per second;
hence we need 7 square feet area of flue, or seven flues, each having
1 square foot of area. It is safe to say that there are not twenty
school-houses in the United States which have fresh-air flues of
sufficient area; the deficiency is made up, for the most part, by
leakage of the outer air through cracks around windows and directly
through the wall, and also by the passage of air from the central hall
into the room, this last air coming from the cellar or basement.
The velocity of the air at the foul-air registers and in the foul-air
ducts may be greater than in the fresh-air flues, since there is no
danger of its causing draughts, and hence there is no truth in the
common notion that the outlets should be larger than the inlets to
allow for the expansion of heated air. It is important that the
velocity of the current in the outlet shaft or chimney should be at
least 8 feet per second at the point where it escapes into the outer
air; and if the outlets be too large for the inlets, the result may be
that some of the foul-air flues will work backward and become inlets.
The plan of making everything a little larger than is necessary is not
a safe one as regards chimney-flues and outlet shafts.
The merits of a plan of ventilation depend not only on the amount of
air introduced, but on its distribution. The test for distribution is
chemical analysis of samples taken in different parts of the room and
at different levels. A very good idea of the direction taken by the
incoming air can also be obtained by the use of fumes of nascent
muriate of ammonia, as above described. In considering the
distribution which will probably take place in a given plan, care
should be taken not to fall into the common error of supposing that
because pure carbonic acid gas is heavier than air, therefore the
carbonic acid derived from respiration sinks to the floor, and that
special provision should be made to remove it at that point. The law
of the diffusion of gases effectually prevents this separation and
sinking of the carbonic acid from the mixture of gases expired, and it
will be found to be present in about equal proportions in all parts of
an inhabited room.
The methods of introducing and distributing fresh air depend to a
great extent upon the methods of heating employed; and it is necessary
to remember that while good ventilation is a very desirable thing,
satisfactory heating is, in cold weather, still more desirable, and
must be attained even if the ventilation is interfered with for that
purpose. The principal difficulty in the way of securing good
ventilation is its cost. In a cold climate satisfactory heating, good
ventilation, and cheapness are not compatible; it is comparatively
easy to obtain any two of them, but impossible to have the three
together. This fact should be fully understood and realized by the
physician, for its comprehension will save much time in considering
the merits of various patent ventilators and ventilating appliances,
which, according to their inventors, produce good ventilation at no
expense beyond that of the original cost of the apparatus; which is
practically about the same as a claim to have discovered perpetual
motion. Patent ventilators are usually cowls to be placed upon the top
of outlet {181} flues. I know of none which are superior to the common
Emerson Ventilator, on which there is now no patent. In cold weather
the air must be warmed to secure comfort; it must be changed to secure
ventilation. The changing of the air carries off heat, the loss of
which must be supplied by fuel, which fuel costs money. The greater
the ventilation, the more rapid the change and the more heat required.
It is therefore quite possible to judge somewhat of the merits of a
heating and ventilating apparatus--for example, of a
school-house--from the amount of fuel consumed; but the conclusion
will be precisely the reverse of that drawn by the average trustee,
since it will be, that within certain limits the less fuel required
the less satisfactory the apparatus.
The evil effects of insufficient ventilation, although very certain
and very serious, are not immediate, or such as to attract attention
at first, except in very aggravated cases with excessive
over-crowding. The power of the organism to adjust itself to
surrounding circumstances is very great, and perhaps as great in
regard to the endurance of foul air as anything else. Yet this power
is greater in seeming than in reality, for at last such air produces
disease and shortens life. Its effects are manifested in diseases of
the respiratory organs, acute and chronic, and it is now generally
admitted that the undue prevalence of phthisis in troops is due to the
foul air of the barrack-rooms.
Some persons are much more susceptible than others to the effects of
impure air, and will suffer from headache, languor, loss of appetite,
etc. where others would experience little inconvenience. Children thus
susceptible dread the school-room as ordinarily constructed and
ventilated, and their discomfort should be taken into account and
guarded against.
Thus far, reference has been made only to those impurities of air due
to respiration and lights; in other words, the necessary impurities
found in human habitations. The impurities due to sewer gases will be
referred to hereafter; they should be prevented absolutely, and not
provided for by ventilation. One of the most difficult problems
presented to the physician is to determine whether the effluvia from a
given locality are injurious to health, and if so, to what extent.
These effluvia may be due to certain occupations or manufactures, or
they may result from the disposal of excreta, from obstructed drainage
giving rise to swamps and the collection of decaying organic matter,
and in other ways. The best definition of the term "injurious to
health" in this connection is perhaps that suggested by Dr.
Ballard--_i.e._ that exposure to the offensive effluvia causes bodily
discomfort or other functional disturbance, continuing or recurring as
the exposure continues or recurs, and tending by continuance or
repetition to create an appreciable impairment of general health and
strength, to render those exposed more liable than others to attacks
of disease, and more apt to suffer severely when attacked, and, in the
more serious forms, to the direct production of the disease and the
shortening of life.
The group of symptoms due to offensive effluvia is, as Dr. Ballard
remarks, a tolerably constant one, and consists of loss of appetite,
nausea, headache, giddiness, faintness, and a general sense of
depression, with, in some cases, vomiting and diarrhoea. But it is
usually impossible to prove by statistics that these phenomena are due
to a given effluvium complained of, for those who suffer from it are
usually exposed to other causes of ill-health, such as poverty,
overcrowding, collection of filth, etc.; and, on the {182} other hand,
many of those exposed to the effluvium seem to suffer very little, if
at all, from their surroundings. And so true is this, that in the
carefully prepared report upon effluvium nuisances recently issued by
Dr. Ballard,[2] it will be found that as a rule no attempt is made to
prove that the effluvia from any particular branch of industry are
injurious to health; the test practically applied is that they produce
offensive odors.
[Footnote 2: _Report in respect of the Inquiry as to Effluvium
Nuisances arising in connection with various Manufacturing and other
branches of Industry_. By Dr. Ballard, London. Her Majesty's
Stationery Office, 1882, 8vo.]
The legal view of this subject is given in the various decisions as to
what should be considered a nuisance, the essence of which is the use
of one's own property in such a way as to inflict damage upon, and
injure the rights of, another. If a man collects on his own premises,
for his own use, any material, such as water or filth, he is bound to
retain it within his own premises or to let none of it escape in such
a way as to damage others; and this holds good as regards gases,
vapors, and odors. The decision of Mansfield, in the case of Rex _vs._
White, is often quoted approvingly by jurists, viz.: "It is not
necessary that the smell be unwholesome; it is enough if it renders
the enjoyment of life uncomfortable." But, practically, the question
as to whether the discomfort produced is sufficient to produce
ill-health will be the one upon which the physician is called to give
evidence, and the one also upon which he will find it most difficult
to obtain data sufficient to enable him to form a positive opinion.
III. IMPURE WATER.--Of all the various preventable or removable causes
of disease to which the attention of the physician engaged in practice
in the small towns and rural districts is directed, it will usually be
found that the water-supply is the most important, because it is in
these localities that it is most liable to become contaminated in such
a way as to produce sickness.
All water used for drinking purposes is impure in the chemical sense,
since it contains some inorganic matters or salts, and in most cases
organic matter also. It is difficult to define precisely what should
be considered an impure water in a sanitary sense, and the best we can
do is to indicate probabilities in the absence of positive evidence of
the production of disease by the suspected water. So far as inorganic
impurities are concerned, the most important, from the sanitary point
of view, are the salts of lead, magnesia, and lime, but in this
country these are so rarely the cause of disease that they hardly
require special notice. The physician should, however, bear in mind
possibilities of lead-poisoning in some obscure cases which he will
meet.
The diseases due to impure water are certain specific fevers,
diarrhoeal diseases, and some affections due to parasites which find
entrance to the body through this medium. The water-supply is to be
suspected in case of prevalence of diarrhoeal disease in a community,
and especially if the outbreak be sudden and affect a number of
persons and families. Sudden outbreaks of cholera, typhoid fever, or
malarial fever, confined to a limited locality, should lead to careful
examination of the water-supply. The impurity in water which causes
these diseases is supposed to be either organic or the product of
organic life, and at present the prevailing opinion is that the really
dangerous impurities consist of minute living organisms or {183}
germs. It is usual to estimate the impurity of water by the amount of
organic matter present, but it is evident that this alone can give no
positive information, since by this standard milk and soup would be
very dangerous. Much depends upon the character of the organic matter,
whether it is derived from the animal or vegetable kingdom--whether it
is in a state of fermentation or putrefaction, etc. etc.; but the
presence of specific germs in it is the most important part of all,
and at the same time the most difficult to ascertain. Nitrogenous
organic matter in a state of decomposition is dangerous, yet it does
not always produce disease, even when ingested in comparatively large
quantity, as in case of "high" game or tainted meat; and it is easy to
find instances where water strongly polluted with sewage has been used
for a considerable period without producing marked ill effects. It is,
however, so extremely probable as to be for practical purposes
certain, that water contaminated with the discharges from persons
suffering from certain diseases will produce similar diseases in those
who drink it, and there is also enough evidence that water containing
filth of various kinds either produces or promotes disease to warrant
much more attention to this subject than has heretofore been bestowed
upon it.
The chemical examination of a suspected water is by no means a simple
process, and in most cases had better be referred to an expert in such
matters. It is highly desirable, however, that the physician should
have sufficient technical knowledge to be able to make a rough
analysis at least, if for no other reason than that he may be able to
appreciate the results reported by the chemist. As a rule, when a
water is so polluted with decomposing organic matter as to be
positively dangerous it will have an unpleasant odor, which is best
developed by half filling a quart bottle with the water to be examined
and shaking it thoroughly. The so-called simple and ready methods
which are from time to time advocated in the newspapers, such as the
addition of sugar to the suspected water and allowing fermentation to
take place, the use of tannin as a precipitant, or the decolorization
of a solution of potassium permanganate, are really of very little
value and should not be relied upon. In the hands of an expert the
best simple method of determining the quality of a water is by
evaporation of a known quantity and the ignition of the solid residue.
From the amount of the total residue, the quantity left after
ignition, the amount of blackening produced, and the odor, a very fair
opinion can be formed as to the amount of organic matter present, and
whether it is of animal or vegetable origin.
It is not within the province of this paper to describe the methods
used by chemists in water analysis, of which the principal are known
as the Franklin and Armstrong, the Wanklyn, and the permanganate
methods. A careful examination of these methods has recently been made
under the direction of the National Board of Health, and a preliminary
note of the results, prepared by Professor Mallet, has been published
in the _Bulletin_. From this it appears that the chief value of
chemical analysis is, first, the verification of gross pollution,
which will usually be detected by the appearance and smell of the
water; and, second, in periodical examination of a water-supply to
detect changes from the normal or usual character of the water, which
may be taken to have a certain local standard of purity. Special
importance is attached to the careful determination of {184} nitrates
and nitrites in water to be used for drinking, these being the results
of oxidation of organic matters, and therefore giving evidence of
previous contamination.
Prof. Mallet concludes that "there are no sound grounds on which to
establish such general standards of purity as have been proposed,
looking to exact amounts of organic carbon or nitrogen, albuminoid
ammonia, oxygen of permanganate consumed, etc., as permissible or not.
Distinctions drawn by the application of such standards are arbitrary
and may be misleading." While this is perfectly true, considered from
the standpoint of scientific precision, it does not sufficiently take
into account the value of probabilities in these matters, considered
as motives to action. It is perfectly true that there can be no fixed
standard--that a water which the chemist would report as relatively
pure might be much more apt to produce disease than one which he would
pronounce impure--but it is nevertheless true that from the results of
chemical analysis, taken in connection with evidence as to the source
and history of the water, an opinion can be formed as to the danger
from its use which is sufficiently reliable to be acted upon in the
absence of positive evidence, such as the production of disease.
In many cases the matter must be doubtful, and Prof. Mallet truly says
that it will not do in all such cases to forbid the use of the water,
for it often happens that this should not be done unless it is
absolutely necessary; but there are many other cases in which there is
very little doubt, and where action should be governed by the
probabilities.
The microscopical examination of suspected waters sometimes gives
decided indication as to the nature of the impurities; and it may be
that hereafter, in connection with physiological tests, it will become
of even more importance than the chemical. To determine the presence
of organisms in a sample of water the best method known at present is
to kill and coagulate them by means of osmic acid or chloride of
platinum, and allow them to subside. This method is of course
inapplicable if it be desired to use them for either culture- or
inoculation-tests.
Chemists have no uniform system of reporting the results of their
analyses, some using grains per gallon, U.S. or Imperial as may be,
and others parts per hundred thousand or per million of the water. It
is therefore difficult to appreciate the value of the figures as given
by them. The following, in parts per 100,000, will enable the
practitioner to form a general estimate of the character of analytical
reports; but the opinion in individual cases is so modified by the
coincident amounts of chlorine, ammonia, nitrous and nitric acids,
that the experienced sanitarian only is qualified to put on the
results an estimate which shall be in accordance with our present
knowledge of such matter:
_Upland Surface-Waters_.
Allowable. Doubtful. Impure.
Total organic elements to .4 .4 to .6 Over .6
Oxygen required to .3 .3 to .4 " .4
Albuminoid ammonia to .015 .015 to .025 " .025