CONDUCTION OF HEAT 



441 



(b) Moistness. 'Vhv loss of heat depends on iiie luoistness of the 

 surface. The thermal coiuluetivity of all li(|iii(ls except mercury 

 is very low. Water may be boiled in the toj) portion of a test tube 

 without aft'eetinti; a piece of ice at the bottom. 



TABLE LXVIII 

 Thermal Conductivity 



Several measurements of the temperature inside the body have 

 been made. The natural cavities, e.g. the rectum, and vagina, 

 are generally used, both being deep cavities into which the ther- 

 mometer or thermal elements can be inserted for a considerable 

 distance. Measurements have been made of the temperature in 

 the inside of the stomach in patients with gastric fistulae. The 

 temperature of freshly voided urine was suggested by Stephen 

 Hales in 1731 as representing that of the interior of the body. 

 It has been found that, while the temperature of the surface of 

 the body is about 32° C, as the depth from the surface increases, 

 the temperature rapidly rises till the depth of about 5 em. is 

 reached. It continues to rise much more slowly for the next 

 2 cm. or so. Apparently the temperature after this is fairly 

 uniform, i.e. 37° C. That is. the subcutaneous tissues cause a 

 temperature lag or thermal gradient of about 5° C. This is due to 

 the large proportion of water which enters into the composition of 

 the tissues, giving the body the high specific heat of about 0"83, 

 A man weighing 60 kg. would consequently have a water equiva- 

 lent of 50-4 kg. of water, so that a rise of 0*1° C. would only be 

 registered after 50-4 Cals. of heat had been rendered latent. 



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

 and of the subcutaneous tissue. A good layer of subcutaneous fat 

 which has a low thermal conductivity will decrease the rate at 

 which heat arrives at the surface and retard heat loss. The 

 epidermis is a poor heat conductor. It is twice as bad as fat and 

 three times as poor as the corium. 



