HYGIENE OF RESPIRATION AND VENTILATION 169 



evaporating more water from the skin. At 70° it begins to be 

 uncomfortable and to affect the efficiency of our work. 



2. Moisture. The more moisture there is in the air, the slower 

 the evaporation will be, and the more heat the body will retain. 

 The lower the humidity, the more rapidly will water evaporate, 

 and the more rapidly will the body lose heat. A hot, stuffy 

 room interferes with breathing and comfort because it interferes 

 with the radiation of heat and evaporation of water in the lungs. 



Ordinary air 



Carbon dioxid 0.03"^, 



Expired air 



Nitrogen 78.09 5« 



Carbon 

 dioxid 

 4.1 i 



Fig. 88. Effect of breathing on the air 

 The ratio of oxygen to carbon dioxid is changed from 700: i to 4: i 



The advantage of large spaces in workshops and other places 

 where people are likely to be crowded together is that they make 

 it possible for the heat and moisture given off by the body to be 

 removed fast enough to insure comfort. The amount of oxygen 

 or of carbon dioxid seems to have nothing to do with the diffi- 

 culties of suitable ventilation. 



The drowsy effects of a badly ventilated room are due to the conges- 

 tion, or crowding, of the skin capillaries with blood and the corresponding 

 lack of blood in the brain and the muscles. In the Black Hole of Cal- 

 cutta, in which so many people lost their lives, the victims were supposed 

 to have died from lack of oxygen. It seems more likely that in such 

 cases death really results from heat stroke, due to the excessive humidity 

 (from the perspiration and lung transpiration of the people) and the 

 high temperature (from the heat radiated by the bodies). 



