with fresh, warm air at high pressure; and every outlet is connected with the foul air room in the basement at low pressure, produced by the exhaust fan. The exhaust steam from the engine is injected into the heating coils and utilized for warming the building. Thus the Thus the only expense for running the fans is in the heat units actually converted into mechanical units as the steam passes through the engine. It will thus be readily seen that in manual training schools, where power is needed for other purposes, the cost of ventilating the building is very small. But even in ordinary school buildings the economy and efficiency of mechanical ventilation will undoubtedly in a few years be generally recognized. The fan system has been introduced into all the public school buildings of Chicago, though in many

of them it is still in an imperfect and undeveloped stage.

Many engineers do not yet recognize the ne cessity of combining the plenum and exhaust movements, confining the ventilation usually to the plenum only. This is, it seems to me, a serious error. With a proper exhaust supplementing the plenum, water closets may be placed in the basement and in other parts of the building and perfect ventilation secured for them. Every closet bowl should have independent downward connection with low pressure. In such an arrangement, with the fresh air inlets connected with high pressure, the rooms will be entirely free from impure air and foul gases. G. B. MORRISON, Principal Manual Training School.

Kansas City, Mo.

MANY important investigations have recently been made, in this country and in Europe, to determine the actual condition of schoolrooms, and the sources of discomfort and danger to health under varying conditions. The purpose of this paper is to give the results of some of these investigations, and to call attention especially to the sources of danger connected with the air in the schoolroom. The expired air.

We are still in a good deal of uncertainty in regard to the constituents of expired air and their influence upon health. We are certain of one thing. While outdoor air contains about twenty-one volumes per hundred of oxygen, expired air contains only about sixteen volumes. Hence, by decreasing the amount of oxygen, if in no other way, the presence of fifty persons in a confined space like a schoolroom tends to decrease the healthfulness of the conditions. Thus, negatively, expired air is injurious, because deficient in oxygen. It is probable that some of its constituents are also more or less positively injurious. In the light of recent in vestigations, one is cautious about expressing an opinion here. Some years ago carbonic acid (CO2) was deemed the injurious constituent of expired air, and some curious ideas about ventilation were based upon this belief.

But it was found that one could remain without discomfort in an atmosphere where the percentage of CO, was far in excess of that in the worst ventilated rooms.

Then the organic matter in expired air, the anthropotoxine, as some of the Germans called it, was deemed the really deleterious constituent. Brown-Sequard and D'Arsonval in 1887 reported experiments that indicated that expired air contains a volatile organic poison. This injected into rabbits caused death. In 1889 they reported new experiments that corroborated their previous views. Rabbits were confined in a series of metallic cages, connected by means of rubber tubing. The apparatus was so arranged that the animal in the last cage received air vitiated by all the air expired by the other rabbits. The animal in the next cage received the expired air from those beyond, and so on. The result was that the animal in the last cage died first, then after an interval the one in the next cage, while those in the first and second cages usually remained alive. By placing absorption tubes containing concentrated sulphuric acid between the last two cages, the rabbit in the last cage remained alive, while that in the next to the last was the first to die. These experiments of BrownSequard and D'Arsonval seemed to substanti

ate the theory that there is an organic poison in expired air. And their results have played quite a role in works on hygiene that have appeared since that time. Nearly all the standard hand-books speak of the organic matter in expired air as largely or chiefly the cause of the injurious effects produced by such air. The writer of this paper must admit that he has himself said the same (Ped. Sem., vol. II., No. 1, p. 23). He consoles himself, however, with the thought that at the time he was in good company. But, although in a report of more recent experiments Brown-Sequard and D'Arsonval reaffirm the validity of their former results, recent experiments by Lehmann and Jessen, by Haldone and Smith, and others, notably by Drs. Bergey, Billings, and Mitchell in this country, have made it doubtful whether the organic matter in exhaled breath is harmful. (See the paper by the last mentioned writers on "The Composition of Expired Air and Its Effects Upon Animal Life," Smithsonian Contributions to Knowledge, Washington, 1895, from which the following citations are made.) "Lehmann and Jessen confined a man, clothed in his working clothes, in a zinc cage for about half an hour, then allowed a boy and girl to inhale the air from the cage. No ill effects except increased respirations to 30 or 40 per minute were noticeable." They had also negative results from injecting condensed fluid into animals.

"Haldane and Smith, in 1892, published an account of experiments in which an air-tight chamber, 6 feet 2 inches high, 2 feet 11 inches wide, and 3 feet 11 inches long, was employed. Samples of air for analysis were drawn off through a tube placed in the wall of the chamber, about three feet from the floor. When one person remained in this chamber until the vitia. tion was from ten to twenty times as great as in the most crowded and worst ventiliated public buildings, there was no perceptible odor or sense of oppression. Air vitiated to such an extent as to completely prevent a match from burning had no appreciable effect upon the subject of the experiment." The Brown-Sequard experiments were repeated by them; but the results of their investigation were against the theory that a volatile poison, other than carbonic acid, exists in expired air.

Dr. Bergey's experiments.

Dr. Bergey, under the direction of Drs.

Billings and Mitchell, experimented upon animals, and also tested the air expired by a healthy man, a consumptive, and a man with a tracheal fistula. In an extended series of experiments they found no bacteria in expired air, no evidence of an organic poison; and the Brown-Sequard and D'Arsonval experiments were repeated, but with very different results. Some of the conclusions drawn from this very important investigation are as follows:

"The results obtained in this research indicate that in air expired by healthy mice, sparrows, rabbits, guinea pigs, or men there is no peculiar organic matter which is poisonous to the animals mentioned (excluding man), or which tends to produce in these animals any special form of disease. The injurious effects of such air observed appeared to be due entirely to the diminution of oxygen, or the increase of carbonic acid, or to a combination of these two factors. They also make it very improbable that the minute quantity of organic matter contained in the air expired from human lungs has any deleterious influence upon men who inhale it in ordinary rooms, and, hence, it is probably unnecessary to take this factor into account in providing for the ventilation of such rooms.

Past theories doubtful.

The results of this invesitgation, taken in connection with the results of other recent researches summarized in this report, indicate that some of the theories upon which modern systems of ventilation are based are either without foundation or doubtful, and that the problem of securing comfort and health in inhabited rooms requires the consideration of the best methods of preventing or disposing of dusts of various kinds, of properly regulating temperature and moisture, and of preventing the entrance of poisonous gases like carbonic oxide derived from heating and lighting apparatus, rather than upon simply diluting the air to a certain standard of proportion of carbonic acid present.

Other sources of contamination.

Whether or not further invesitgations corroborate Dr. Bergey's results, it is evident that there are other sources of contamination of the air of schoolrooms besides the expired breath of the pupils. Some of these are mentioned in the following paragraphs:

The various sources of bad odors.

The schoolroom smell is proverbial. The cause of this odor noticed in passing from the outer air to an unventilated room is unknown. "It may in part be due," as Dr. Bergey points out, "to volatile products of decomposition contained in the expired air of persons having decayed teeth, foul mouth, and certain disorders of the digestive apparatus; and it is due in part to volatile, fatty acids given off with or produced from the excretions of the skin and from clothing soiled with such excretions."

Recent investigations indicate that bad odors may have a greater effect upon the comfort and health of children than we have supposed, especially in case of very susceptible persons. Decaying teeth.

Here should be mentioned one of the sources of contamination of the air of schoolrooms to

which little attention has been given, namely, the decaying teeth of the children. Many interesting investigations of the teeth of school children have been made in England, France, Germany, and this country. Perhaps the most extensive investigations are those of Dr. Rose in Germany, who examined the teeth of 13,667 school children-a total of 233,339 teeth. (See Zeitschrift fur Schulgesundheitspflege, 1895.) He found that the number with defective teeth varies greatly with the locality. But the number was large in all places, as shown in the following table:

to bad odor from the mouths of his patients, but that even he again and again found it hard to stay in the schoolrooms when conducting his examinations, because of the bad breath of the pupils, and that he often pitied the teacher and the pupils who had to remain six hours in such an atmosphere. When one thinks of the number of pupils usually crowded into a limited space, and of the frequent poor ventilation, it is evident that this is a matter of some importance.

The various sources of dust-dirty shoes and clothes, dirty books, chalk, etc.

Some interesting investigations of the dust of schoolrooms have been made. Hesse found in a Berlin schoolroom 2,000 micro-organisms. per cubic meter of air before school; 16,500 during the time of instruction, and 35,000 at the end. The number depends largely on the conditions that favor the stirring up of the dust. Ignatjeff found similar results in Russian schools, as shown in the table.

Meyrich, a teacher in a Leipzig school, has made a similar investigation by a different method, and found some very interesting results. In the school where the tests were made the regulations indicate that a good deal of care was taken to keep the rooms clean. The janitors were required to sweep the rooms at least twice a week, oftener at the wish of the director, and the stairways and corridors daily. According to the regulations, in sweeping a large amount of moist sawdust must be used, the seats raised, and the dust carefully removed. A few hours afterward the furniture was dusted and the seats wiped with moist cloths. cloths. All the rooms must be thoroughly scrubbed at least five times a year, together with the windows, doors, etc. In spite of these

The investigation was carried out with German thoroughness. Tests were made to determine the number of micro-organisms in the dust that was swept up. Meyrich estimated that there were at least a million micro-organisms to a gram of dust. The fine dust that settles on the seats and furniture was also tested, and the number to a gram was estimated as 4,354,635. Now from these tests it appears that an enormous number of micro-organisms adhere to the dust and pass into the air. The significance of the figures cited is seen by comparison with the number found in mountain or sea air. It is said that in tests of the air on the high mountains in Switzerland, Frendenreich often had to seek through two or three cbm. of air before he found a single bacterium. Cleanliness and bacteria.

In

The studies of other investigators have shown that the number of micro-organisms stands in inverse ratio to the adequacy of the means of ventilation, the cleanliness of the room, and the cleanliness of the children. most of our schools, I fancy the number is pretty large. Ignatjeff estimated that in the schools where he made his investigations each pupil inhaled 45,000 micro-organisms during the five-hour session. Of course this need not frighten anybody. The bacteria, like the poor, are always with us. Most of them are harmless. Still, some are likely to be pathogenic. Not long since, our health officers here in

Worcester found a child ill with diphtheria sitting with the other children, the disease unsuspected. But then, quite apart from possible danger of infection, the dust is bad for the eyes and the mucous membrane of the respiratory and vocal organs. And further, it is not cleanly to breathe dust and bacteria all the time. Our ideas of cleanliness are peculiar. We turn away in disgust from dirt that we can see; we are not affected by dirt that we can only collect in a test tube or see with a microscope. The problem of cleanliness is the great problem that school hygiene must solve; how to keep the children clean, their clothes clean, their books clean; how to have clean floors, clean furniture, etc. One who finds a practical solution of these questions will be a public benefactor. Meanwhile there is no reason for stirring up the dust as much as possible by dry sweeping and the feather duster, in order that pupils may breathe the maximum number of micro-organisms while we are deciding what is the cheapest and most effective method of cleaning the room without injuring the wood. Dangers connected with the heating apparatus.

The fourth source of danger is connected with the heating apparatus. Sometimes the air is contaminated by small quantities of carbonic oxide and other poisonous substances from the coal used. The most common evil is probably overheating. Our rules in this country put the minimum temperature for schoolrooms so high (68°-70° F.) that the rooms are frequently heated to 75° or 80° F. Such a temperature is probably one chief cause of colds, headache, and general discomfort among school children.

Methods of ventilation.

The limits of this paper will not permit consideration of the sources of danger from the surroundings of the schoolhouse, unhygienic outhouses and the like, nor of practical methods of ventilation. Of course all sources of contamination should be removed as far as possible; but after all adequate ventilation is necessary. This can seldom be had without mechanical methods. The advantages of mechanical over natural ventilation has been shown by numerous investigations. The results obtained by Carnelly (see Jacob, Ventilation and Warming. Appendix, London, 1894), given in the table, will serve as an illustration:

Pedagogical importance of ventilation. The necessity of adequate ventilation should be emphasized from the point of view of pedagogy as well as from that of hygiene. Observers in this country and in Europe have estimated that from fifteen to twenty-five per cent more work is done by the pupils in well ventilated schoolrooms than in rooms badly ventilated. Dr. Lincoln says that the effect of perfect ventilation is to increase the pupil's power of work fifty per cent.

Ignorance and indifference.

Enough has been said to indicate that the

problem of supplying an adequate quantity of pure air in a schoolroom is not a simple one. Many of the questions in regard to the sources of discomfort and danger are still open, and many of the practical problems of heating and ventilation are still unsolved; but while from a scientific point of view our ignorance may be great, our practice is far behind our knowledge. Studies of the actual condition of schoolhouses show that universally accepted norms are ignored in a large per cent of the schools of this country, even in the large cities. Boston may be taken for illustration. The following citations are taken from an account by Mrs. Richards of the recent investigation in that city under the direction of a committee of the Collegiate Alumnæ. ("Municipal Responsibility for Healthy School-Houses," pp. 5-6.)

The Boston investigation.

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The legal re

against 250 required. quirement is a supply of thirty cubic feet of air per minute per pupil. Twenty-four rooms in ten buildings were examined. Six of these, or one-fourth of the whole, showed less than eight cubic feet per minute per pupil; eight rooms gave between eight and twelve cubic feet, and only three rooms showed over twenty cubic feet. The floors of seventy-seven of them, or forty-one per cent of the whole number, had never been washed since laid, until the summer of 1895. * A total of 126

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old-style flush and privy vaults still remained, after having been condemned year after year by the board of health. Only 27 out of the 186 schoolhouses of Boston were found to have anything like adequate fire escapes." "It is probably within the limits of truth to state that if the laws now on the statute books were enforced as strictly in respect to schoolness, there would be 20,000 children on the houses as to private houses and places of busistreets of Boston next September on account of the closing of buildings which have been allowed to be used year after year in defiance of all legal and moral law.”

Conclusions.

In view of these recent studies, a few prac tical inferences seem to be justified.

1. While at present there is some doubt about the injurious elements in expired air, there is no reason to diminish the present standards of air supply. Two thousand to three thousand cubic feet of fresh air per pupil should be brought into the schoolroom each hour. hour. The cubic air-space per pupil should be two hundred to three hundred cubic feet, never less than two hundred cubic feet.

2. Sources of contamination that have often

been disregarded, dust, bad odors, excess of moisture, overheating, and the like, appear to be of very grave significance. One of the most important means of avoiding these sources of danger, however, is a good system of heating and ventilation; but even this is not enough to make the schoolroom atmosphere hygienic, unless great care is also taken for the highest degree of cleanliness of the children, of the furniture, the blackboards, the books, etc.; and for removing dust, avoiding overheating, bad odors, etc.

3. The system of heating and ventilation. should be determined beforehand and incorporated in the plan of the building.