THE TEMPERATURE OF THE BODY 1315 



The main regulation of heat loss thus takes place by the control of 

 the nervous system over the cutaneous circulation and the sweat- 

 glands. Besides these channels of heat loss, others may play an 

 important part under certain conditions. Heat is lost to the body in 

 warming the food and air which are taken in. It is also lost in respira- 

 tion in the evaporation of water and the setting free of C0 2 from 

 watery solution into the expired air. The following estimate, by 

 Tigerstedt, represents the proportion of losses in an adult man by 

 these different ways : 



A. WARMING THE FOOD AND AIR 



(1) 1500 g. water drunk at 15 C. and warmed to 37-5 raised Cal. 



therefore 22-5 .... . = 33-75 



(2) 1500 g. food eaten at 25 C. (mean) and warmed to 37-5 raised 



therefore 12-5 ; specific heat 0-8 . = 15-00 



(3) 15,000 g. ( = 11,500 1.) air respired at 15 C. and warmed to 37-5 



raised therefore 22-5 ; specific heat 0-237 . = 79-95 



128-70 

 B. Loss OF WATER AND C0 2 IN THE BREATH 



(4) It is assumed that the inspired air is half saturated with watery 



vapour at 15 C. and that the expired air is fully saturated at 

 37-5 C. Approximately 450 g. of water would be given off 

 therefore in the form of vapour from the respiratory passages ; 

 the latent heat of the water vapour is 0-537 Cal. . 241'70 



(5) The absorption of heat in the liberation of C0 2 from the lungs 



(800 g.); 0-134 Cal. per g. 



348-90 

 From above . . 128-70 



Total 477-60 



The sum of heat losses specified under these five headings amounts 

 to 477-60 Gal. Estimating the total heat loss of an adult man at 

 2400 Cal., this sum represents only about 20 per cent, of the 

 total. The remaining 80 per cent, (in round numbers) takes place 

 through the skin. 



If we estimate the total heat loss of an adult man at 2400 calories, 

 we may say that about 5 per cent, of the total heat loss takes place 

 by warming the food and air, about 15 per cent, by the evaporation of 

 water and C0 2 in respiration, and about 80 per cent, by radiation 

 and convection and the evaporation of sweat from the skin. The pro- 

 portion represented by the last factor will increase very largely in the 

 presence of a high external temperature, or of an excessive heat pro- 

 duction in consequence of violent muscular exercise. 



