ANIMAL HEAT 453 



temperature in physiological conditions does not rise, the assumption is 

 that the food is oxidized in the body to urea, carbon dioxid and water with 

 the liberation of the foregoing amounts of heat and their equally rapid 

 dissipation. 



Assuming 2500 Calories to be an average of heat liberated during a day 

 of repose, the losses, in the ways stated in the foregoing paragraph, may be 

 tabulated as follows: 



1. In Warming .Food and Drink. The average temperature of food and 



drink is about i2C.; the amount of both together is about 3 kilograms; 

 the specific heat of food about 0.8 that of water. The absorption 

 of body-heat therefore by the food amounts approximately to 3X0.8 

 X25C. = 60 Calories = 2.8 per cent. With the removal of the end- 

 products of the foods and drink from the body an equal amount of 

 heat is carried out, 



2. In Warming the Inspired Air. The average temperature of the air 



is i2C.; the amount of inspired air, about 15 kilograms; the specific 

 heat of air, 0.26. The absorption of body-heat by the air until it at- 

 tains the temperature of the body will therefore amount to 15 Xo.26X 25 

 = 97.5 Calories = 3. 8 per cent. The expired air removes from the 

 body a corresponding amount. 



3. In the Evaporation of Water from the Lungs. The quantity of water 



evaporated from the lungs may be estimated at 400 grams; as each 

 gram requires for its evaporation 0.582 Calorie, the quantity of heat 

 lost by this channel would be 400X0.582 = 232.8 Calories=9.4 per 

 cent. 



4. In the Evaporation of Water from the Skin. The quantity of water evapor- 



ated from the skin may be estimated at 660 grams, causing a loss of 

 heat by this channel of 660X0.582 = 384.1 Calories=i5.3 per cent. 



5. In Radiation and Conduction from the Skin. The amount of heat lost 



by this process can be indirectly determined only by subtracting the 

 total amount lost by the above-mentioned channels from the total 

 amount produced. Thus, 2500777.44=1725.6 Calories = 69 per cent, 

 would represent the average amount lost by radiation and conduction. 

 The Mechanism of Heat-dissipation. As stated in foregoing para- 

 graphs heat-dissipation is accomplished mainly by radiation and conduction 

 from the skin, 70 per cent., and by evaporation of water from the skin and 

 lungs, 25 per cent. The heat dissipated in warming food, drink and air 

 inspired, or what amounts to the same thing in raising the excretions, urinary, 

 fecal and respiratory to the body-temperature, may be here neglected. 

 The relative amounts dissipated by these two routes, radiation and evapora- 

 tion of water, will depend largely on the external temperature in so far as 

 it is not interfered with by clothing and artificial temperatures. 



The mechanism by which the dissipation is accomplished consists of 

 the cutaneous and respiratory blood-vessels and the sweat-glands, together 

 with the heart and respiratory apparatus, which collectively therefore may 

 be regarded as thermolytic organs, all of which are made to cooperate by 

 the intermediation of the nerve system, especially the vaso-motor and 

 secretory portions of it. With a given external temperature such as charac- 

 terizes the spring months, there is a certain ratio between the percentage of 

 heat lost by radiation and by water evaporation. As the temperature rises 



