SECTION IX 

 THE ABSORPTION OF THE FOOD-STUFFS 



THE ABSORPTION OF WATER AND SALTS 



THE intake of water, and probably of salts, by the alimentary 

 canal, in accordance with the requirements of the organism as a 

 whole, seems to be regulated almost entirely by the central nervous 

 system, the higher parts of this system, viz. those concerned with 

 appetite, being particularly involved in the process. Thus in man 

 any large loss of fluid to the body, as by sweating, diarrhoea, haemor- 

 rhage, gives rise to an intense thirst that has its natural reaction 

 in increased intake of water by the mouth. On the other hand, 

 the property possessed by the alimentary canal of absorbing water 

 and weak saline fluids contained in its interior is very little influenced 

 by the state of depletion, or otherwise, of the water depots of the 

 body. It is practically impossible, however large the quantities of 

 fluid ingested, to evoke the production of fluid motions, the greater 

 part of the ingested fluid being absorbed on its way through the 

 alimentary canal. Thus a man may keep himself in perfect health 

 and maintiin the water content of his body constant whether he take 

 one litre or six litres of water daily. The whole process of regulation, 

 apart from that determined by appetite, appears to be carried out at 

 the other end of the cycle, viz. by the kidneys. As concerns absorp- 

 tion of water there is no chemical solidarity between the alimentary 

 surface and the rest of the body. Whenever water is presented to 

 the surface it is absorbed and passes into the circulation. 



The absorption of water in the stomach may be regarded as nil. 

 Although from this viscus alcohol, and possibly peptone and sugar, 

 may be absorbed to a slight extent, water or saline fluids intro- 

 duced into it are passed through the pylorus either without change 

 or increased by the secretion of fluid from the gastric glands. In 

 no case is there a diminution of fluid in the stomach. 



The chief absorption of water occurs in the small intestine. It 

 is on this account that the salient features of cases of dilatation of 

 the stomach with stenosis, absolute or relative, of the pyloric orifice 

 can be nearly all referred to the starvation of the body in water, 

 and can be often relieved by the administration of water either sub- 



cutaneously or by the rectum, i.e. by the channels through which 



82G 



