EFFECT OF HUMIDITY OF AIR 



269 



external temperature 1 C. The negative results obtained by 

 Rubner do not apply to small animals like mice. J. J. R. Macleod 

 and myself have found that air saturated with moisture at 20 C. 

 increases the C0 2 output of mice. In one case after 18 hours' 

 ventilation with wet air we found the mouse almost dead with 

 a rectal temperature of 22-5 C. It recovered in a current of dry 

 warm air. So long as the temperature of the wet chamber was 

 maintained at 24-25 C. the mouse maintained its temperature 

 by increased combustion. At 20 C. the compensatory mechanism 

 failed, and the increased heat loss over-passed the increased heat 

 production. The weight of the mouse fell in spite of the large 

 amount of food it consumed. Mice are, of course, extremely 



Water Output of 

 fasting dog. 

 Heat, Production, 

 Saturation deficit 



19 21 23 25 27 29 31 



Fia. 19. The Effect of Kaising the External Temperature on the Water 

 Output and Heat Production. Saturation deficit indicates relative saturation 

 of air with moisture. (Rubner.) 



susceptible to cold, but prolonged exposure to wet cold air 

 must have a similar though far less marked effect on larger 

 animals. 



To determine the influence of wet air on radiation and conduc- 

 tion, Rubner constructed an air calorimeter surrounded by a water- 

 jacket which was kept at a constant temperature of about 20 C. 

 The animal was placed in a wire cage isolated from the copper 

 walls of the chamber. The heat given out by the animal ex- 

 panded the air in the air-jacket, and this affected a recording 

 spirometer. A copper cylinder placed in the water-jacket, and 

 connected with a second spirometer, recorded any change in the 

 temperature of the water, or barometric pressure. The readings 

 of the second spirometer were used to correct those of the first. 

 The temperature of the incoming and outgoing air was also re- 



