FRESH AIR 325 



into a fever. This fever is accompanied by abnormal chemical changes 

 within his tissues and the production of toxic substances, which in turn 

 react upon his tissues diminishing their working power, inducing early 

 fatigue, and upsetting the normal equilibrium of his organs. The re- 

 sult of such a disturbance of his bodily mechanism, if very pronounced, 

 is the production of a pathological condition which is called heat stroke. 



But the extreme condition of air at a temperature above the bodily 

 temperature and completely saturated is not necessary for inducing the 

 pathological symptoms. We may witness them under somewhat more 

 moderate conditions in the frequent cases of sunstroke which occur in 

 the streets of our American cities on hot and humid days. The ob- 

 servations of Kubner, one of the foremost German hygienists, indicate 

 that even at 75° F., or more than 23 degrees below bodily temperature 

 and with a humidity of only 80 per cent, of saturation an untrained 

 man can continue comfortable only by refraining from physical work. 

 The performance of work under these conditions would throw a tax 

 upon his powers of adaptation. Even at still lower degrees of tempera- 

 ture and humidity the unfavorable symptoms may begin to appear, 

 indeed the point at which our environing air ceases to be comfortable 

 and begins to force us to make special efforts at accommodation to it is 

 one that is not outside our range of frequent experience. 



Many experiments, some of them striking, seem to make it clear that 

 it is to these two features of heat and humidity, the same features which 

 are responsible for sunstroke, and not to others, that all the evil effects 

 of the air of crowded, ill-ventilated rooms are actually due. These 

 experiments have usually consisted in confining and observing men, 

 perhaps several together, in comparatively small experimental cham- 

 bers. Sometimes these chambers have been little more than bare boxes ; 

 sometimes they have been rooms provided with elaborate devices for 

 varying the quantity and qualities of the air. Sometimes the subjects 

 of the experiments have been obliged to breathe over and over again 

 the same air; sometimes the air has been kept under careful control 

 and changed in various ways. The effects of the various conditions 

 have then been observed and recorded. These observations upon 

 human beings have been supplemented by a variety of experiments on 

 animals, and these animal experiments have added greatly to our knowl- 

 edge of the qualities of the air which human beings ought to breathe. 



One of the notable and fruitful investigations was an American one, 

 carried on between 1893 and 1895 by Billings, Mitchell and Bergey 

 with the aid of the Smithsonian Institution in Washington. The 

 Billings of this investigation was the efficient organizer and first libra- 

 rian of the New York Public Library and the Mitchell was our famous 

 physician-author, Dr. Weir Mitchell. Another helpful American con- 

 tribution is that of Benedict, whose work with the respiration calorim- 



