316 A TEXTBOOK OF PHYSIOLOGY 



The experiments showed that breathing increased percentages of 

 C0 2 . and diminished oxygen percentages of 2 to 3 per cent., had little 

 effect in modifying the frequency of the pulse, while the increased 

 temperature and humidity of the air had a profound effect. If the 

 percentage of C0 2 in the chamber were suddenly raised up to 2 per 

 cent., the subjects inside were quite unaware of this. If the air in the 

 chamber were breathed through a tube by a man standing outside, 

 none of the discomfort, experienced by those shut up inside, waa 

 felt. Similarly, if one of those in the chamber breathed through a 

 tube the pure air outside, he was not relieved. The cause of the 

 discomfort was thus proved to be heat stagnation due to the 

 excessive heat and humidity, and absence of movement of the air. 

 The wet and dry bulb thermometers do not indicate the degree of 

 this heat stagnation; this may be measured by the katathermometer 

 described later (see p. 500). 



The cooling power of the atmosphere exerted on the skin depends 

 far more on its movement than on its temperature ; the air in ordinal y 

 rooms with the windows closed is so still that the cooling power 

 approximates to that in the tropics out of doors. The good effects of 

 open-air life depend very largely on the wind and its cooling power 

 stimulating the metabolism of the body. It has been shown that 1he 

 will to perform either mental or physical tasks is diminished by hot, 

 moist atmospheres, the pulse in increased in frequency, the arteiial 

 blood-pressure lowered and the appetite diminished by such. 



