presence to the sense of sight; they are the products of processes constantly going on in the lungs and the skin. This organic matter, though invisible, is not inodorous; it may easily be distinguished on entering a sleeping apartment which has not been "aired" after a night's occupancy. The sickening stench represents an unknown quantity of animal matter thrown off by the body in watery vapor. This fœtid material oxidizes slowly, is difficult to remove, and is readily absorbed by all hygroscopic substances. It clings to the clothing and furniture, permeates the porous walls, lodges in crevices and corners. It undergoes decomposition in the presence of other dead organic matter, such as we have seen our rooms to be plentifully filled with, and this decomposition and putrefaction afford an explanation of the characteristic fœtor.

It is easy, from what has been said, to see how quickly the air of a school-room containing fifty scholars must become unfit to breathe. Add to this the varied effluvia which the clothing of many scholars, especially those of the poorer classes, carries, - a redolence of manifold household occupations, culinary and industrial, and the sources of the foulness of school-room air become more and more apparent, while the necessity is made manifest for incessant vigilance to secure the renewal of the air, to maintain the natural means for the disinfection and oxidization of the decomposing products of molecular decay. If the supply of fresh air is equal to the demand, these organic matters are rendered harmless; if through inattention or through ignorance the pure air is shut out from school-rooms, the children are exposed to a devitalizing material, which is none the less sure in its action because its presence and accumulation are imperceptible to those producing it, and because its actual or relative amount in the atmosphere cannot be measured by more accurate methods than are at present available.

So far as the school-rooms which were inspected are con

cerned in this respect, the tables will show that their condition was not unexceptionable. It will be observed that in general terms a foul odor was perceived in rooms whose atmosphere was most remarkable for carbonic acid impurity; while the rooms which gave the best results as regards the latter impurity gave the least offence to the inspector's sense of smell.

Warmth of School-rooms.

The question of temperature

is intimately related to that of ventilation; indeed, it is impossible to dissociate the two subjects in this climate. During seven months of the year, in our latitude, it is necessary to supply artificial warmth to the air of rooms in which we dwell or work. The atmosphere must be not only pure but also measurably warm, as a condition requisite for health as well as comfort. A temperature like that of our autumn, winter and spring months is depressing to the vital energies, unless, by exercise and proper clothing, the animal heat of the body is enabled to maintain a healthful equilibrium. When the body is at rest, it is impossible to work the brain comfortably or economically in an atmosphere whose temperature is much below 65° Fahrenheit.

On the other hand, an artificial warmth in excess of the proper degree is enervating. Some notion of the probable effect upon health of a continued exposure to a superheated atmosphere, which is at the same time vitiated by respiration, may be obtained by entering almost any of our school-rooms at the latter part of a half-day's session in midwinter. To a sensitive person, leaving the outer air and coming at once into such a room, the impression is one not easily forgotten. The blast of hot, foul air is sickening. The marvel is that children do not more frequently succumb to the inevitably depressing influence of such unwholesome conditions.

The temperature which may be regarded as a reasonable standard for the warmth of school-rooms must be fixed somewhat arbitrarily. We cannot apply here the test of

individual sensitiveness by which the warmth of dwellingrooms is generally governed. The teacher's sensation of comfort ought not to be relied upon as a guide for that of the scholars; for a great diversity exists, not only in the individual idiosyncrasies (and this is especially true of female teachers), but, also, in the needs of the same persons from one day to another. Hence, a properly adjusted thermometer which has been tested by a standard is alone to be trusted in this matter, and its record should be frequently consulted. Bearing in mind that the body in repose suffers more from cold than one in active exercise, and that, other things being equal, children require a somewhat higher degree of warmth than adults, it may be set down as a safe standard rule, that the temperature of school-rooms should range between 65° and 68° Fahrenheit (18.5° and 200 Centigrade). It need hardly be stated here that the ordinary temperature of school-rooms is above 68°, and that a point in excess of 70° is very commonly found. A considerable part of the languor and depression observed in school children may be traced to this cause.

It is proper to call attention here to a practice which is believed to be far too common in school-rooms, and which is the source of great injury to the scholars. It is the sudden cooling of the air of an overheated room by opening the windows widely. If anything is worse than an excessive degree of artificial heat, it is the quick transition to the opposite extreme. It is a frequent thing in school-room experience that the teacher, becoming suddenly aware that the air is too warm for comfort, directs that the windowsashes be opened at the top to effect a speedy relief. The consequence is, that the inevitable wave of cold outside air sweeps over the uncovered heads of the children, and a fresh accession of cases of bronchitis, or of more serious pulmonary affections, is the result. An instance of this thing was observed in the inspection of the Chapman school;

a room showed at the desk-level a temperature of 77°; three quarters of an hour later the same room was re-visited, when the thermometer indicated 61.7°, a fall of 15.3°! Between the two visits the teacher had "aired" the room to some purpose; the air was pure enough, surely, and the coughing and sneezing of the children gave warning that it was cold enough also. If such a sudden change should occur in the outer atmosphere it would be considered a fruitful cause of increased sickness in the community.

Much has been written about the differences of temperature at different levels in a room. Considerable stress has been laid upon the fact that the floor temperature is relatively much cooler than that elsewhere; and the opinion is expressed that health is imperilled thereby. Among recent observers, Dr. Kedzie, of Michigan,* has made much of this point. In an excellent and exhaustive paper on the ventilation of school-buildings, he states that he has frequently found a difference of from 8° to 15° between the temperature at the floor and that at the desk-level (in one instance 19° and in another 21°), and he forcibly entitles the lower stratum of such an atmosphere "a lake of cold air." Careful observations made on this point in our recent inquiry failed to confirm Dr. Kedzie's results. As will be seen by an examination of the tables, the greatest difference found in any of the one hundred and eleven observations was 11.7°, and this was a solitary and very marked exception; the usual difference was much below that, and amounted to two or three degrees only. Undoubtedly, a difference of more than four degrees is very objectionable, and should be guarded against.

The following tables present the results of the schoolhouse inspection in Boston. It should be stated that the column marked "number present" gives the actual attend

*Report of Michigan State Board of Health for 1873, page 74.

ance, the teacher being included with the scholars. The temperature was taken by means of corrected Centigrade thermometers; the readings have been reduced to the Fahrenheit scale, because the latter is better known in this country, and not because it is otherwise preferable. The method employed by Prof. Nichols for the analysis of the air is that known as Pettenkofer's. The temperature of the outer air and the barometric readings are as they were recorded at the Observer's office of the United States Signal service in Boston.