increasing character and strength to Boston, if increasing care be taken by Boston to nurture their minds and bodies healthfully.

In the execution of the instructions of the Board of Health to "make investigations concerning the ventilation of the school-houses of the city," much embarrassment was experienced in the selection of those buildings upon which the observations should be made. To make a thorough inspection of even the majority of the one hundred and fifty school-buildings owned by the city would be out of the question. The purpose of the proposed inquiry would be met sufficiently by presenting the facts concerning a comparatively small number of buildings, so selected as to give an impartial idea of the general condition of things, thus avoiding needless repetition. To this end, ten school-houses were chosen, representing, so far as possible, every variety of distinguishing quality. The age, construction, and locality of the building, its internal arrangements for heating and ventilation, the character of the scholars in attendance with special reference to their passive influence on the school-room air,— all these were taken into the account. Thus, as will be seen by the tables which present the results of the inspection, schoolhouses were visited through all the grades, from the High and Normal to the Primary; of all ages, from the Brimmer, with its full generation of graduates, to the Dudley, just completed; exhibiting a great variety of appliances for ventilation and warming; and accommodating more or less distinctly defined classes of occupants, from the children nurtured in prosperity down to those who had come from narrow courts and alleys, and had brought with them to their studies the characteristic flavor of overcrowded tenement-houses. The buildings thus chosen to represent their entire kind in Boston were called upon for representative facts concerning the matters of heating and ventilation. It was not to be expected that any school-house would give uniform results so far

as its own rooms were concerned, or that the whole series of observations would present a condition of things equally good or bad, throughout; for the circumstances surrounding the inspections would be exceedingly and inevitably various. But even allowing all this diversity, it is believed that the observations here reported give a tolerably satisfactory notion of the average condition of the Boston school-houses to-day.

A single word should be added concerning the manner in which the inspection was conducted. The time chosen in each instance was the last hour of the morning or of the afternoon session, when the room had been occupied at least an hour, and when the air would probably be found at its worst. A specimen of the air was obtained from the middle of the room, the jar being filled at the level of the scholars' heads. At the same time, the temperature of the room was taken at the floor-level and at the level of the pupils' heads. Finally, the condition of the window-sashes and of the ventilating registers, whether open or shut, was noted; and a note was also taken of the state of the atmosphere to the sense of smell, with the number of desks in the room, and the number of children present.

It is proper here to acknowledge the uniform courtesy with which the teachers aided the inspection. Their ready appreciation of the purposes of the investigation, and their earnest hope that tangible improvement in matters of ventilation would be promoted by a report of the facts gathered, afforded evidence that at least one class in the community has an intelligent interest in school-hygiene.

Before the facts obtained are presented in detail, it will be well to make some brief preliminary observations on the special matters involved in this report.

Carbonic Acid. - Chemistry has done much in these latter days toward assigning a true place for this gaseous product of respiration. Formerly, it was thought to be the

essential element for consideration in any discussion about vitiated air, and was regarded, in its relations to respiration, as the poison of which oxygen was the antidote. Now, however, while we are still very far from an exact or exhaustive knowledge of atmospheric impurities, carbonic acid is looked upon as harmful, because it obstructs respiration, and not because it is specifically a poisonous gas; in other words, through its accumulation, the air becomes adulterated, and to that extent is impaired for breathing purposes. According to M. Bernard,* when an animal dies from breathing this gas, its death is owing to the mere want of respirable air; hence he considers its action to be negative or suffocative.

But, however innoxious we may consider carbonic acid to be in itself, it is not without interest as an ingredient of foul air; for it affords us a constant and reliable test of atmospheric impurity. It is the component whose relative amount can be most accurately determined; and, as the other and more harmful parts of a vitiated air are known to bear a tolerably constant relation to this product, we come to look upon the chemical determination of its presence as an accurate guide to our judgment concerning all the rest.

The amount of carbonic acid which the atmosphere may hold before it becomes unfit for respiration is, therefore, a matter of the first importance to ascertain. The proportion of the gas in pure air has been frequently determined to be an average of 0.4 per 1,000, or four volumes in ten thousand. Parkes, the eminent English authority on hygiene,† states that the ventilation of a room is imperfect when it fails to introduce fresh air in sufficient quantity to remove all sensible impurity, so that a person coming from the external air shall not perceive a trace of odor, or any difference between the room and the outside atmosphere in point of fresh*Substances toxiques, page 137.

†Practical Hygiene, fourth edition, page 134.

ness. By repeated experiment, he has found that the organic products of respiration begin to be manifest when the carbonic acid in the air of an inhabited room reaches the proportion of 0.6 per 1,000; in other words, when, by respiration, the relative amount of carbonic acid in the air has become increased by 0.2 in a thousand parts as compared with a pure atmosphere. Pettenkofer, who is at the head of German sanitarians, makes the limit of purity 0.7 of carbonic acid in a thousand volumes of air, beyond which an unwholesome degree of vitiation begins.

While it is obvious that a system of ventilation is not to be expected which, in this climate at least, shall make the indoor air precisely identical with regard to purity with the outdoor, if any error is made in fixing the standard it should be on the safe side. Accordingly, the percentage adopted by Parkes is chosen as the normal measure by which to determine the comparative purity of the air of Boston school

rooms.

1

The general tables which appear elsewhere in this report give the results in this direction as they were found by Prof. William Ripley Nichols, upon the analysis of specimens of air taken by himself in each of the one hundred and eleven school-rooms inspected. From these tables is compiled the following exhibit, giving at a glance some of the fruits of the inquiry into the amount of carbonic acid in the rooms of the ten buildings visited.

This shows for each school-house the greatest and the least quantity in any single room, and the average of all the rooms, the figures representing parts in 1,000:

Organic Impurities. - A ray of sunlight entering a darkened room through an aperture of the closed shutter makes manifest certain remarkable physical qualities of the air. The display is not reassuring. If the experiment be made in even an undisturbed and unoccupied apartment, a dusty cloud is disclosed. If the floating particles be subjected to microscopic examination, the effect is still more suggestive; the impalpable dust-cloud then assumes positive characters, and is found to consist of the "detritus of every imaginable thing used in our social economy; clothing, food, organic emanations from our bodies and those of the lower animals, shoe-leather, mineral particles raised from the earth, besides the germs of infusorial life concerned in all the processes of putrefaction and decay.'

But beside the dust which is in suspension in the air of rooms, there are organic elements which do not betray their

* Derby. Anthracite and Health. 2d Ed., page 15.