PREVENTION OF HEAT LOSS 349 



A. Physical Regulation Preventative. (Usually effective be- 



tween 40 and 20 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 cooling surface 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 

 have been covered with a layer of impenetrable varnish. It is 

 alleged that, at the enthronement of Pope Leo X., a boy was 

 gilded to represent an angel. Before the ceremony was finished 

 the boy, despite the efforts of Leonardo da Vinci and other 

 physicians, had died. That excessive heat loss was the cause of 

 this accident is proved by the experiments of Valentin. He 

 showed that, under similar circumstances, the carbon-dioxide 

 output of the subject was reduced to about 1/6 of the normal, 

 i.e. metabolism was at a low ebb. If the animal were kept 

 normally warm, the carbon-dioxide output returned to a normal 

 figure. On the other hand, Senator states that the human body 

 can be covered for 8-10 days with an impenetrable layer without 

 producing any disturbance of metabolism. He avers that, in 

 those cases where vasodilatation occurred, some toxic substance 

 must be i absorbed from the varnish. 



m 



Alcohol produces vasodilatation an increased cooling surface. That 

 is, this drug, because it causes more warm blood to come to the surface, 

 gives rise to a sensation of cutaneous warmth while at the same time 

 materially aiding in the depletion of the body's store of heat. 



B. Chemical Regulation Curative. (Usually predominant below 



20 C.) 



These mechanisms come into play to replace heat which has 

 been lost. 



(a) Voluntary or involuntary work. We have already seen 

 that work causes the liberation of heat and we have discussed 

 the reason for this. Shivering, or involuntary work is a reflex 

 act which occurs in any person of normal muscular tone when the 



