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pors, and solid particles which are thrown into it from a variety of sources. Those arising from habitations and works of man are the most important, from a hygienic point of view, both because we are constantly exposed to their influence and because they are most completely subject to control.

A cubic foot of air contains a little less than a cubic inch of carbonic acid. A cubic foot of air, as it comes from the lungs, contains upwards of seventy cubic inches of carbonic acid.

As carbonic acid is constantly generated within the body, we may regard the presence of a certain small amount of it as quite compatible with health. But when not promptly eliminated, its action becomes quickly injurious. Two volumes in one thousand of air causes headache and vertigo in many persons. Air containing one per cent. of it is soporific and depressing. From five to eight per cent. renders it dangerous to breathe, while from ten to twelve per cent. makes it speedily destructive to life. Adults inhale fourteen cubic feet of air an hour.

Air exhaled contains four or five per cent. carbonic acid, or more than one hundred times the normal proportion in pure air, and also is saturated with moist vapors.

Volatile substances and effete matter are also the products of respiration and perspiration. Such atmosphere is unfit to support life, and when breathed habitually and insidiously, often unsuspected, causes deterioration of vigor and health.

It is estimated that at least forty per cent. of all fatal diseases are directly or indirectly due to impure air.

Carbonic acid, in itself, is not poisonous, but acts as an obstructor of respiration, by preventing the oxygen of the air from being absorbed by the lungs. It is not impossible to live for a short time in atmosphere containing three per cent. of the gas produced artificially, but a small proportion of carbonic acid in air continually thrown off by respiration, indicates a highly deleterious condition of the atmosphere.

Such an atmosphere is far more injurious to the health of our children, originating, as it many times does, in rooms occupied by children of uncleanly habits.

Billings says: "There are less microbes found in sewer air than in streets" and quotes (proceedings of Royal Society). Carnelly and Haldane of London, state that Dundee sewers contain twice as much carbonic acid, and have three times as much organic matter as outside air, and fewer microorganisms, and remarks that this air in the sewers is better than in naturally, or even mechanically ventilated schools. Organic matter is a common impurity of the atmosphere, and is often present in dangerous proportions. It exists in the form of vapor and suspended matter, and is found most abundantly diffused in the air of dwellings, hospitals, and schoolrooms. In health it is thrown off through the lungs by the process of respiration, and also by exhalations from the skin. That coming from the lungs consists of organic vapor, holding in suspension epithelium cells that have been detached from the mucous surfaces of the air passages, pharynx, mouth, etc. By the skin more is given off, such as fatty matters, epidermic debris, and also small quantities of urea.

The presence of an excess of carbonic acid in the air, denotes in nearly every case a lessened proportion of oxygen, and if the air has been contaminated by breathing, a decided increase in the amount of organic matter. These conditions make it dangerous, but whether this danger is due to the extra quantity of carbonic acid and organic matter, or to the absence of oxygen, or partly both, does not matter. But it is sufficient to know that the three conditions are commonly associated in air contaminated by respiration.

The following have been attributed to overcrowding and inadequate ventilation of schoolrooms: anorexia, constipation, vomiting, diarrhea, coated tongue, prostration, drowsiness, headache, Bright's disease, clonic and tonic spasms, coma, tonsillitis and inflammation of the throat in general.

The transmission of infectious diseases by foul air has not been proven by past researches, but we know the above ailments may be produced in this way. The possible causes of diphtheria are many. Perhaps it is their very multiplicity which is confusing and bewildering.

We have found that to preserve good health, the capacity of a room should not be less than six hundred to one thousand cubic feet for each adult occupant, in cases where the ventilation is temporarily imperfect; and the volume of fresh air required is five hundred to one thousand cubic feet per hour for each child. This may seem a large amount, but on a calm day the atmosphere has a velocity of at least two miles an hour, and a body of ten square feet gets ventilation by one hundred thousand cubic feet pure air per hour.

I do not consider that the size or the capacity of the room is of as much importance, as that the warming and ventilation shall be in a perfect condition. I really feel like condemning the old practice of heating by stoves as inadequate both as to warmth and ventilation, especially the latter. Ventilation is very slight where stoves are used, as it requires a very small amount of air to support combustion. The temperature is not uniform in the schoolroom, as the circulation is sluggish.

When outside air is at zero, and the two sides are exposed, there is a difference of 4.5° in every foot of height. The atmosphere is a favorable medium for germs and in a cold. room they tend to fall to a low level and hence might often be breathed by children, when taller persons would escape them altogether. But this cannot hold good absolutely, as in warm rooms they would be distributed throughout the atmosphere to some extent if the rooms were well ventilated. But in case the ventilation is slight, as when stoves are used, the lower stratum holds nearly all. Carbonic acid should not be allowed to get higher than six or eight ten-thousandths for respiration. Streets, in some localities, have as high as fifteen

ten-thousandths, some schools as high as fifteen to thirty-one ten-thousandths, while one school is reported, in Paris, having fifty-seven ten-thousandths.

Another source of danger is in the soft crayons used, which with other causes, produce a great quantity of dust found diffused in the atmosphere with other impurities.

The production of moisture is inadequate in nearly every system of heating. I have been in schoolrooms where the system was such that the air might be either received from outside, or might return from the room for reheating. In one particular case I have in view, there were sixty-five pupils present. The janitor was returning the air from the room for reheating over and over again, while the water-pans supplying the furnace had been entirely neglected, thus allowing no admixture of moisture whatever. Passing to the ventilator I found the draft was not sufficient to draw out the flame of a lighted match held directly over the flue. The janitor told me that for some reason the furnace did not work properly, and that no air had been received from outside for three months except what would find its way in from natural

causes.

Cases of vertigo were of frequent occurrence in this room. Can we expect better health in our race, when they are subjected during their earlier and most trying years to such vitiated atmosphere?

SCHOOL HYGIENE: LIGHTING OF SCHOOLROOMS AND ITS RELATIONS TO ANOMALIES OF

REFRACTION.

BY J. A. BACH, M. D., OF MILWAUKEE,

PROFESSSOR OF THE DISEASES OF THE EYE AND EAR, WISCONSIN COLLEGE OF PHYSICIANS AND SURGEONS.

It is a well-known fact among oculists that nearly all eyes at birth are far-sighted, and that as the general development of the body proceeds, the eyes approach nearer and nearer to the normal, and under certain conditions the relative length of the anterior posterior axis of the eyeball may, by stretching or abnormally rapid growth, go beyond the normal and produce near-sightedness. Unequal curvatures in the different meridians of the eye, especially of the cornea, produce astigmatism, which as a rule, does not change much. This condition, outside of a few exceptions, is a congenital one.

Persons whose occupations do not necessitate close vision, such for instance as may be found among the Indians, rarely lose all their far-sightedness in this development, and as a class are a far-sighted people. On the other hand it is the active oculist's daily observation that persons who apply themselves to close work from childhood, as a rule, not only lose this far-sightedness, but a very large percentage of them become near-sighted in a greater or lesser degree. Especially is this so where the conditions are such as to necessitate a close approximation to the work under unfavorable surroundings. This tendency to the development of near-sightedness is most marked during the years of active growth, when the tissues are soft and unresisting. Any influences that produce an abnormal congestion of the eye with a consequent poor circulation in this organ, tend to favor the development of anomalies of the refraction by lowering the resistance of the

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