but are met with in dwelling-houses, churches, lecture-rooms, halls, work-shops, and especially in railway cars.

Pure air to breathe, pure water to drink, pure food to eat, and a pure soil to live upon constitute four of the essential conditions of healthy existence. The first only of these conditions, pure air, as affecting the health of persons who spend a portion at least of their lives in such places as I have just mentioned, I propose to make the subject of this paper.

I.

QUANTITY.

And first as to the quantity of air essential to health under the conditions named. This embraces the two topics, (a) the amount of air-space essential to health and (b) the amount of fresh, out-door air to be supplied for each person per hour or per minute. It is quite clear that these two points have a definite relation to each other, since in any given case, with a definite amount of air-space and a like definite and constant supply, and with a given number of inmates in an apartment, if the cubic airspace is diminished, the air supply must be increased in order to maintain a like condition of purity of the air of the apartment, the number of inmates remaining the same, and vice versa.

(a) In school-rooms the amount of cubic air-space should be at least 200 cubic feet for each scholar of average age, and more for older pupils.

A room of 10,000 cubic feet, measuring about 30 by 25 by 13 feet, would afford for forty persons an air-space of 240 cubic feet for each, with a liberal allowance for the space taken by furniture and the occupants themselves. In an estimate of the amount necessary for school-rooms, allowance may be made for recesses and intermissions, and consequent opportunity for entire or partial renewal of air by opening doors and windows.

In a railway car carrying passengers and containing 3,000 to 3,500 cubic feet of air-space the space for each person will vary from 40 cubic feet upwards, as the car is full or nearly empty, an amount far too small if the air is not rapidly changed by ventilation. In a sleeping-car, and especially in the lower berths, with walls shut in on every side, with about forty-five to fifty

cubic feet of air to each berth, and with scarcely any opportunity for its renewal, the condition of the occupant at night is somewhat like that of premature burial, so far as air supply is concerned.

The ventilation of an ordinary railway car in winter, when in motion, with air considerably elevated in temperature above that of the surrounding air, would appear to be an easy matter, and such is the fact, the chief difficulty being to exclude smoke, cinders, and dust. This may be done quite effectually by admitting air at the rear end of the car, which can be readily accomplished, even when the car is in rapid motion, so long as arrangement is made for its aspiration at the top of the car. Train officials and the janitors of schoolhouses and other public buildings should be instructed in the proper management of ventilators, and required to use them for the health and comfort of the occupants, a matter that is usually neglected.

(b) What amount of fresh air should be supplied to each person per hour or per minute?

Forty feet per minute may be taken as a minimum for adults; some authorities place the required amount as high as sixty feet. For young children, using a smaller amount for respiration, less than either of these amounts is requisite, especially in rooms frequently opened at recesses or intermissions. Two thousand feet per hour for each pupil, except in higher grades of schools, may be deemed sufficient.

66

Dr. Billings says, in his recent treatise on this subject, that perfect ventilation can be said to have been secured in an inhabited room only when any and every person in that room takes into his lungs at each respiration air of the same composition as that surrounding the building, and no part of which has recently been in his own lungs or in those of his neighbors, or which consists of products of combustion generated in the building, while at the same time he feels no currents or draughts of air and is perfectly comfortable as to temperature, being neither too hot nor too cold."

THE QUALITY OF THE AIR NECESSARY FOR THE HEALTH OF OCCUPANTS OF SCHOOL-ROOMS OR OTHER APARTMENTS.

2. This topic naturally succeeds that already named, since it furnishes the reason for the change in the air of apartments when occupied. In order to treat this subject intelligently, a brief statement of the composition of the air is here necessary.

Pure out-door air is composed of 79 parts of nitrogen, 20.96 of oxygen, and .04 of carbonic acid, and also a small amount of watery vapor.

Of the parties to this mixture the carbonic acid has special importance in connection with the subject of air supply, not because of actively poisonous qualities, as is the case with carbonic oxide, but because it is an exponent of the respiratory impurity of the air. Other dangerous products of respiration are doubtless evolved at the same time with the carbonic acid, and hence the amount of carbonic acid which is capable of measurement is taken as an expression of the entire product.*

* Billings on Ventilation and Heating.

There appears to have been a change of opinion as to the action of this gas upon the health of those who breathe it, and also as to certain other properties which it possesses. In consequence of its greater weight, it was for a long period taken for granted that carbonic acid would necessarily be found at the bottom of occupied rooms. Actual determinations, however, have shown that this gas, as well as others, is quite equally dif fused throughout apartments.

There can be no doubt that the injurious effects of carbonic acid have been overestimated by confounding it with its excessively poisonous namesake, the carbonic oxide (or carbon monoxide), and I am also inclined to the belief that there has been too great a reversion of opinion in the direction of a belief in its harmlessness. The case of workmen in bottling establishments has been cited as an instance of its innocuous qualities, such men being constantly exposed to the liberation of free carbonic acid. In this case, however, there is quite a difference from that of persons exposed to the air of crowded apartments, since the carbonic acid is added to the normal air in the former case, while in the latter it is evolved at the expense of a portion of the oxygen of the room.

Dr. Angus Smith says upon this point that he had always considered carbonic acid as remarkably innocent, in small quantities, and was accustomed to look on the organic substances as the real evils; but his experiments in a tightly closed leaden chamber so far changed his mind that he was inclined to believe that carbonic acid had an injurious influence even in small amounts.*

The amount of carbonic acid added to the air of an apartment by an adult is about three fifths of a cubic foot per hour. At this rate one man would add to the air of a tightly closed apartment of 10,000 feet of air-space three cubic feet in five hours, raising the amount present to six or seven parts in 10,000, the exact ratio depending upon the amount previously present. In order, therefore, to reduce this amount to that consistent with health, a renewal of 3,000 cubic feet per hour, or 50 feet per minute, would

*"Air and Rain," by Robert Angus Smith, p. 179.

be required, and this amount would also be necessary for each added occupant.

Dr. Billings estimates twenty-five to thirty cubic feet per head and per minute as sufficient for school children.

A special reason for attention to the quality of the air supply, with reference to its pollution, is the enormous quantity which we use daily. We are wont to consider the quality of a water supply as a matter of the highest importance to the consumer, and justly so, and also to estimate the impurity of water by the number of grains per gallon, or parts per 100,000; and if we find a minute trace of ammonia or of other impurities, especially in connection with possible causes of pollution, we regard it as a dangerous water; and yet the average daily amount of water drank by each person is but a fraction of a gallon. On the other hand, when we consider the air supply, we find that each child at school takes into his lungs from 300 to 500 gallons of the air of the school-room in the five hours of his daily attendance, and each mechanic or operative in a work-shop breathes at least 1,000 gallons of the air of the shop in ten hours of labor. It is therefore a matter of the highest importance that the air should be pure and that the waste products of respiration should be removed as rapidly as possible and replaced by the pure out-door air. This is especially necessary in the case of work-shops and factories where processes are conducted in which dust or injurious gases are superadded to the products of respiration.

Combustion, both by fires and for heating, and also by gaslights, lamps, and other similar forms of lighting, has an effect upon the air similar to that of respiration, a single gas-burner producing six feet of carbonic acid per hour, which is eight or ten times as much as that produced by one adult. More thorough ventilation is therefore required for occupied apartments at night than by day, unless they are lighted by electric lights.