340 



REGULATION OF TEMPERATURE 



What we want to get at is the mechanism whereby the body 

 temperature of the higher mammal is kept fairly constant despite 

 variations of outside and ' inside ' temperature. In this re- 

 spect, they obey the ordinary laws of cooling surface phenomena. 

 Heat may be lost by : 



I. Conduction and convection. 



la. Ingestion and excretion. Inspiration and expiration. 

 II. Radiation. 

 III. Evaporation of moisture. 



I. Conduction. 



By conduction is meant the loss of heat from a body at a higher 

 temperature to one at a lower temperature by passage from 

 particle to particle, for example, the passing of heat along a poker, 

 one end of which is in the fire. The amount of heat lost by the 

 body in this way depends on several factors. 



(i) Surface exposed, (a) The loss of heat varies directly with 

 the area of the surface exposed. For example, the flow across 

 two square metres is double that across one square metre. The 

 area of surface of a child of 2 years weighing 10 kg. is 5120 sq. cm., 

 and of a man of 60 kg. is 14,079 sq. cm. That is, the area per 

 kg. for a child of 2 years is 512 sq. cm., and for a man is 234 sq. cm. 

 It is obvious that weight for weight the child will lose more heat 

 than the man. 



(b) The loss of heat depends on the moistness of the surface. 

 The thermal conductivity of all liquids except mercury is very 

 low. Water may be boiled in the top portion of a test tube without 

 affecting a piece of ice at the bottom. 



TABLE LVI. 



THERMAL CONDUCTIVITY. 



(c) The loss of heat depends on the nature of the surface and 

 of the subcutaneous tissue. A good layer of subcutaneous fat 



