Production of Heat and Work. 83 



further regulated by the production of sweat and the vaporization 

 of water from the lungs. The clothing of man and the thick skin, 

 hair, wool, and feathers of animals also check and control the loss 

 of heat. 



According to Howell, 1 the heat lost from the human body escapes 

 as follows : 



Heat lost 

 Avenue of escape Per ct. 



By urine and feces 1.8 



By warming expired air 3.5 



By vaporizing water from lungs 7.2 



By evaporation of water from skin 14.5 



By radiation and conduction from skin 73.0 



Total 100.0 



The relative importance of these channels of heat loss depends 

 upon various conditions and upon the species of animal. Animals 

 that do not sweat give off more heat by the lungs and less by the 

 skin. In proportion to their weight small animals lose relatively 

 more heat by radiation than do larger ones of the same species. (96) 

 High external temperature tends to diminish the loss by radiation 

 and increase that due to evaporation from the skin or vaporization 

 from the lungs. Violent exercise calls for the rapid burning of 

 food and tissue fuel, with a consequent increase of body heat. This 

 heat passes off by the more rapid breathing and by the increased 

 losses from the skin. 



In humans the loss of heat is largely controlled by the clothing 

 worn. As a consequence, man has, in some measure, lost his power 

 of heat regulation. With many of the warm-blooded animals, how- 

 ever, the reverse is true, as is admirably shown by the following 

 table of Rubner 2 giving the heat lost by a small dog before and after 

 the removal of his coat of long hair. 



Loss of heat by a dog before and after being shaved. 



The table shows that the coat of the dog prevented the loss of heat 

 from his body, so that no more heat was lost at a temperature of 



1 Text Book of Physiol., 1907, p. 861. 



2 Gesetze des Energieverbrauchs, 1902, p. 14. 



