278 THE HUMAN BODY. 



that part of the vaso-motor centre which governs the gastric 

 arteries. 



Taking Cold. This common disease is not unfrequentlj 

 caused through undue reflex excitement of the vaso-motor 

 centre. Cold acting upon the skin stimulates, through the 

 afferent nerves, the portion of the vaso-motor centre 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 readily passes into inflam- 

 mation. The action is of course primarily protective, to 

 prevent too great loss of heat from the Body; but if internal 

 organs be weak or diseased or if the exposure to wet or cold 

 be prolonged, it is apt to be followed by catarrh or inflam- 

 mation of more or less of the respiratory tract causing bron- 

 chitis, or of the intestines causing diarrhoea. In fact the com- 

 mon summer diarrhoea is far more often due to a chill of the 

 surface, causing intestinal catarrh, than to the fruits eaten 

 in that season which are so often blamed for it. The best 

 preventative is to wear, when exposed to great changes of tem- 

 perature, a woollen 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 and 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 contrac- 

 tion 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 succeeded 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 abso- 

 lute time can be stated, as the reaction is more marked and 

 lasts longer in strong persons, and in those used to cold bath- 

 ing, than in others. 



