328 ESSENTIALS OF PHYSIOLOGY. 



pointed out, the intestinal movements are independent of the central 

 nervous system, it can be shown that these nerves exert a controlling 

 influence. Stimulation of the vagus is followed by contraction of the 

 muscle of the intestinal wall after a preliminary relaxation, but has no 

 effect on the ileo-colic sphincter. Stimulation of the splanchnic nerve 

 results in a general relaxation (fig. 124), but in contraction of the ileo- 

 colic sphincter. The vagus and sympathetic fibres to the small 

 intestine are distributed in the first instance to the myenteric nerve 

 plexus lying between the layers of the muscular coat. The influence 

 of the central nervous system on the intestinal movements is shown in 

 their inhibition as a result of pain, and also in their exaggeration in 

 consequence of emotional conditions. The movements of the intestinal 

 wall are increased by pilocarpine, which stimulates the nerve endings 

 of the vagus. The nerve endings are paralysed by atropine, the effect 

 of which is antagonistic to that of pilocarpine. 



The Passage of the Intestinal Contents from the Ileum into the 

 Caecum. Observations with the aid of Rontgen rays show that the 

 material in the small bowel tends to accumulate behind the ileo-colic 

 sphincter, and that it passes into the caecum in considerable quantity 

 when the sphincter relaxes. The immediate cause of the relaxation of 

 the sphincter appears to be a nervous reflex (gastro-ileac), which follows 

 the entrance of a fresh meal into the stomach. The delay in the ileum 

 will obviously favour the absorption of the last traces of nutritive 

 substances. 



SECTION V. 

 ABSORPTION IN THE SMALL INTESTINE. 



The absorption of the food-stuffs is almost entirely limited to the 

 small intestine. It has been proved that no water is absorbed in the 

 stomach, and although some experiments have seemed to indicate that 

 there may possibly be some absorption of peptone, sugar, and more 

 especially alcohol in that organ, the quantities concerned are, at the 

 most, so small as to be negligible. It will be shown later that a large 

 amount of water is absorbed in the large intestine, and that there is a 

 possibility of the absorption of small amounts of dextrose there also, 

 but, under normal circumstances, the material which reaches the large 

 bowel is free from sugar, as well as all other nutritive digestive 

 products. 



The progress of absorption can be investigated by the method 

 already referred to of collecting the intestinal contents by means of 

 fistulee after the ingestion of a weighed meal. For example, after a 



