Resp iration 1 8 1 



Hence any action of the vaso-motor mechanism which 

 causes dilatation of the cutaneous capillaries leads to a 

 larger flow of blood through the skin and will tend to cool 

 the body. On the other hand, when by the same mechan- 

 ism the cutaneous vessels are constricted there will be a 

 smaller flow of blood through the skin, which will serve to 

 check the loss of heat from the body. 



Again, the special nerves of perspiration act directly as 

 regulators of temperature. They increase the loss of heat 

 when they promote the secretion of the skin, and diminish 

 the loss when they cease to promote it. 



272. How the Bodily Temperature is adjusted during 

 Exercise. The practical working of this heat-regulating 

 mechanism is well shown when we take exercise. The 

 bodily temperature rarely rises as much as a degree dur- 

 ing vigorous exercise. The respiration is increased, the 

 cutaneous capillaries become dilated from the quickened 

 circulation, and a larger amount of blood circulates through 

 the skin. The presence in the skin of so much blood stim- 

 ulates the sweat glands to increased activity, resulting in 

 a free perspiration. A large amount of heat is thus lost 

 to the body, sufficient to offset the addition caused by the 

 muscular contractions. 



This topic is again treated in the description of the skin 

 as a regulator of the bodily temperature (sec. 291). 



273. Effect of Alcohol upon the Respiration. Alcohol 

 tends to diminish the breathing capacity of the lungs. 

 This effect follows from its partial paralyzing influence 

 upon the sympathetic nervous system. 



The enfeebled respiration explains (though it is only one 

 of the reasons) why habitual users of alcoholic liquors can- 

 not endure a normal amount of vigorous and prolonged 

 exertion. The hurried circulation produced by intoxicants 



