THE PHYSIOLOGICAL PRINCIPLES OP VENTILATION 757 



"After 44 minutes the dry-bulb thermometer stood at 87 F., the wet bulb at 83 F. 

 The carbon dioxide had risen to 5.26 per cent. The oxygen had fallen to 15.1 per cent. 

 The discomfort felt was great; all were wet with sweat and the skin of all was flushed. 

 The talking and laughing of the occupants had gradually become less and then ceased. 

 On putting on the electric fans and whirling the air in the chamber the relief was im- 

 mediate and very great, and this in spite of the temperature of the chamber continuing 

 to rise. On putting off the fans the discomfort returned. The occupants cried out for 

 the fans. No headache or after effects have followed this type of experiment which 

 has been repeated five times." (Leonard Hill) Long before the discomfort had become 

 extreme 'the oxygen percentage became so low that matches would not light. The disin- 

 clination to smoke cigarettes was not noticed until some time after it was impossible 

 to light them. 



In other experiments of similar type the person in the cabinet was allowed 

 to breathe outside air through a tube, but with no amelioration of the un- 

 comfortable feeling, or a person outside the chamber breathed for hours 

 the air inside it through a tube without suffering any discomfort. Clearly 

 therefore neither the chemical nature of the air, nor the presence of toxic 

 substances in it, has any relationship to its evil influence. But the experi- 

 ment is not merely destructive of previously held hypotheses ; it also points 

 the way to the true solution of the problem, for it indicates that stagna- 

 tion of air loaded with moisture has some very close relationship to the 

 discomfort. It shows that a change in the physical rather than the chemical 

 properties of the air is the real cause of its deleterious action. 



THE RELATIONSHIP BETWEEN THE PHYSICAL CONDITION OF THE AIR AND 

 THE WELL-BEING OF THE BODY 



The changes observed in the preceding experiment can affect but one 

 function of the body, namely, that of heat dissipation, and by so doing 

 cause disturbances in the mechanism of heat control. This does not nec- 

 essarily imply that this disturbance is so great as actually to cause an in- 

 crease in the body temperature, although this is very commonly observed 

 in persons who have been for some time in crowded places, but it interferes 

 with a mechanism which is responsible not alone for proper heat regulation 

 but also for the maintenance of a correct relationship of blood supply 

 to different parts of the body, and for tonic stimulation of the nervous 

 system. 



It is in connection with this phase of the subject, more than any other, 

 that many people find it difficult to understand the true significance of 

 relative humidity to the well-being of the body. The difficulty depends 

 on the fact that the relative humidity has an opposite influence at low 

 and high temperatures. In the former case it increases the conductivity 

 of the atmosphere for heat and has a cooling influence, and in the latter 

 it interferes with the evaporation of sweat, and v has a heating influence. 

 Below about 65 F. the cooling effect of moist air is prominent because 

 there is little sweating, therefore a cold wet atmosphere is chilling it 



