256 TEE HUMAN BODY. 



membrane lining the empty stomach is pallid and its ar- 

 teries contracted, but as soon as food enters the organ 

 it becomes red and full of blood; the food stimulating 

 afferent nerve-fibres there, which inhibit that part of the 

 vaso-motor centre which governs the gastric arteries. 



Taking Cold. This common disease is not unfrequent- 

 ly caused through undue reflex excitement of the vaso- 

 motor centre. Cold acting upon the skin stimulates, through 

 the afferent nerves, the region of the vaso-motor centre gov- 

 erning the skin arteries, and the latter become contracted,, 

 as shown by the pallor of the surface. This has a two-fold 

 influence in the first place, more blood is thrown into in- 

 ternal parts, and in the second, contraction of the arte- 

 ries over so much of the Body considerably raises the gen- 

 eral blood-pressure. Consequently the vessels of internal 

 parts become overgorged or " congested," a condition which 

 readily passes into inflammation. Accordingly prolonged 

 exposure to cold or wet is apt to be followed by catarrh or 

 inflammation of more or less of the respiratory tract caus- 

 ing bronchitis, or of the intestines causing diarrhoea. In 

 fact the common 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 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 exter- 

 nal 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 maintain the cutaneous 

 circulation; for this purpose movement should be persisted 

 in, or 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 suc- 

 ceeded by a dilatation causing a warm healthy glow on the 

 surface. If the bather remain too long in cold water,, how- 

 ever, this reaction passes off and is succeeded by a "more 



