340 THE HUMAN BODY 



heat from it, thus counteracting the effects of the higher surround- 

 ing temperature. 



Quite similar phenomena occur under proper conditions in many 

 parts of the Body. The mucous membrane lining the empty 

 stomach is pallid and its arteries contracted, but as soon as food 

 enters the organ it becomes red and full of blood ; the food stimu- 

 lating afferent nerve-fibers there, which inhibit that part of the 

 vasomotor center which governs the gastric arteries. 



Taking Cold. This common condition is not unfrequently the 

 indirect result of undue reflex excitement of the vasomotor center. 

 Cold acting upon the skin stimulates, through the afferent nerves, 

 the portion of the vasomotor center governing the skin arteries, 

 and the latter become contracted, as shown by the pallor of the 

 surface. This has a twofold influence in the first place, more 

 blood is thrown into internal parts, and in the second, contraction 

 of the arteries over so much of the Body considerably raises the 

 general blood-pressure. Consequently the vessels of internal parts 

 become overgorged or " congested," a condition which is espe- 

 cially favorable to inflammation. The best preventive is to wear, 

 when exposed to great changes of temperature, a woolen or at 

 least a cotton garment over the trunk of the Body; linen is so good 

 a conductor of heat that it permits any change in the external 

 temperature to act almost at once upon the surface of the Body. 

 After an unavoidable exposure to cold or wet the thing to be done 

 is of course to restore the cutaneous circulation; for this purpose 

 movement should be persisted in, and a thick dry outer covering 

 put on, until warm arid dry underclothing can be obtained. 



For healthy persons a temporary exposure to cold, as a plunge 

 in a bath, is good, since in them the sudden contraction of the 

 cutaneous arteries soon passes off and is succeeded by a dilatation 

 causing a warm healthy glow on the surface. If the bather remain 

 too long in cold water, however, this reaction passes off and is suc- 

 ceeded by a more persistent chilliness of the surface, which may 

 even last all day. The bath should therefore be left before this 

 occurs, but no absolute time can be stated, as the reaction is more 

 marked and lasts longer in strong persons, and in those used to 

 cold bathing, than in others. 



Adrenalin. The effect of this hormone upon the vascular system, 

 as stated previously (Chap. XVIII), is to stimulate the vaso- 



