448 



THE REGULATION OF TEMPERATURE 



only a slight increase, while on the warmer clay with almost the 

 same humidity, the men became uncomfortably hot, and the heart- 

 rate was increased. Under these conditions man is not an efficient 

 machine. 



The effect of the temperature and the humidity of the external 

 air on the loss of heat from the body is very well marked in those 

 people endowed with a good layer of adipose tissue. As has 

 already been mentioned, this dense non-conducting material is a 

 very effective heat insulator, thus preventing rapid heat loss. 

 In hot weather and during exercise, fat subjects become unduly 

 heated. If, in addition, they have poorly functioning sweat 

 glands, then severe or prolonged work becomes impossible. 



The following table (LXXI.) gives a rough indication of the 

 amount of heat lost per day through the various channels : 



TABLE LXXI 



1. Radiation and conduction 



2. Evaporation (a) lungs, etc. 



(6) skin 

 a. Excreta (a) CO. . 



(6) urine and faeces 



Total heat loss per day 



Calories per day. 



1,792 

 182 

 364 



84 

 48 



2,470 



The question now under consideration is, provided some 2,500 

 Calories of heat are lost per day, («) how is excessive heat loss 

 prevented, and (b) how is the amount lost made good ? 



A. Physical Regulation — Preventative. (Usually effective up to 

 30° C. and over 40° C.) 

 This is obtained by decreasing the effective cooling surface, a 

 result which may be produced in three ways : 



1. By wearing clothes (or fur), a layer of still air is established 

 between the body and the outer air. Heat will then be lost from 

 the covered area by radiation only (see clothes). 



2. A good layer of subcutaneous fat prevents a rapid diffusion 

 of heat from the interior to the exterior of the body. 



3. Constriction of the cutaneous blood vessels, a reflex act, 

 results (a) in a decrease in the amount of blood carried to the 

 surface, i.e. decrease in effective cooling siu'face, and (b) in a 

 decreased output from the sweat glands. 



Paralysis of the vasomotor nerves leads to vasodilatation. 

 This is given as the reason for the death of animals whose skins 



