270 



EFFECT OF HUMIDITY OF AIR 



corded. Rubner found that if 100 Calories were lost by radiation 

 and conduction when the air was dry, 107 would be lost in this 

 way at 75 per cent, relative dryness, 116 at 50 per cent., and 125 

 at 25 per cent. In other words, 1 per cent, increase of humidity 

 raised the loss by radiation and conduction 0*32 per cent. A 25 

 per cent, increase in humidity equalled in effect a change in ex- 

 ternal temperature of 2 C. In the case of warmed air (2530 C.) 

 the evaporation of sweat proved to be a factor of greater moment, 

 a 50 per cent, increase of humidity having the same effect as an 

 increase in temperature of 5 C. A temperature equal or above 

 that of the body cannot be tolerated if the air be saturated with 

 moisture. The favourable conditions of relative dryness of the air 

 for workers are at 18-20 C., 60-40 per cent, relative dryness ; at 



Water Output, 



Co z Output 



Saturation; deficit 



3O 33 34 3 



FJG. 20. Effect of raising External Temperature on Water 

 and CC>2 Output (Rubner). 



15 C., 30 per cent, relative dryness ; and at 25-30 C., as dry as 

 possible ; at 25-30 C., 30-40 per cent, relative dryness is dis- 

 tinctly unfavourable (Wolpert). 



To study the effect of varying the temperature under conditions 

 of constant humidity, Rubner constructed a chamber which he 

 surrounded with a water-jacket and kept at a constant temperature. 

 The urine and faeces of the animal fell into a vessel of rape-oil, 

 and sinking to the bottom did not influence the cutaneous and 

 respiratory output of water which was measured in the ventilation 

 air. In a small animal such as the guinea-pig the minimum output 

 of water occurred at 15 C. At lower temperature, in spite of 

 the greater relative saturation of the air with moisture, the loss 

 of water increased a physiological reaction due to the increased 

 respiration and rate of metabolism excited by the cold. In larger 

 animals this reaction is not marked. 



