ii THE THEEMIC ECONOMY OF THE OEGANISM 75 



They may be divided into two groups : those regulating the 

 loss and those regulating the production of heat. In the main- 

 tenance of the thermic balance much importance attaches to the 

 means for the regulation of the loss of heat, i.e. those by which 

 this loss is increased when the temperature of the body is raised, 

 and diminished when the temperature is lowered below the normal 

 average. 



The heat developed by the body is partly used to warm the 

 air inspired and the cold liquid and food taken, but the greater 

 part of it passes into the environment by radiation from the 

 surface of the body, evaporation of water from the skin and the 

 lungs, and exhalation of carbon dioxide from the lungs. 



According to the approximate calculations made by Helmholtz 

 and Eosenthal the quantities of calories lost in twenty-four hours 

 from these various sources in an adult are apportioned as follows : 



1. Water 1500 grms., heated from 15 to 37-5 . . . = 34 calories 



2. Food 1500 grms., heated from an average temperature of 



25 to 37-5 C. (specific heat 0'8) = 15 



3. Air inspired about 15,000 litres, heated from 15 to 37'5 C. 



(specific heat 0'237) 80 



4. Water discharged in the form of vapour, about 450 grms. 



(latent heat 0'592 calories) = 266 



5. Carbon dioxide discharged by the lungs, about 800 grms. 



(0-118 cal. per grm.) = 94 



Total 489 



Since the sum total of heat lost by an adult in a condition of 

 equilibrium of thermic balance amounts on an average to 2400 

 cal., we may estimate the daily loss through the skin at about 

 1911 cal. 



Mammals and birds possess natural means of reducing or 

 delaying the loss of heat, which enable them to attain an average 

 temperature which is very high in proportion to the quantity of 

 heat developed by them. These means of defence against the loss 

 of heat are the subcutaneous layer of fat and the fur or feathers 

 with which the skin is covered. Man, having no fur, instinctively 

 covers himself with clothes, which fulfil the same purpose as the 

 fur of mammals and the feathers of birds. The layer of adipose 

 tissue is a bad conductor, and diminishes the loss of heat from the 

 muscles to the cutaneous surface ; the fur, feathers, and clothes 

 diminish the radiation of heat from the cutaneous surface to the 

 surrounding air. Coverings, whether natural or artificial, raise 

 the stratum of air which comes into immediate contact with the 

 skin to a temperature somewhat over 30. Since air is a bad 

 conductor of heat, four times less than wool, it is easy to explain 

 why the surface of the skin which is covered with clothes has a 

 temperature varying from 33 to 35 C., while the exposed parts 

 are much colder. If the fur of a dog or rabbit be removed by 



