326 ESSENTIALS OF PHYSIOLOGY. 



test rneal 77 per cent, of the protein was converted into proteose and 

 peptone, and one-half to three-fifths of the starch into dextrin and 

 sugar, as a result of gastric and duodenal digestion, and that, when the 

 intestinal contents reached the lower end of the ileum, the digestion of 

 all the food-stuffs was complete. 



THE MOVEMENTS OF THE SMALL INTESTINE. 



The intestinal contents are slowly propelled along the gut towards 

 the colon, and at the same time they are subjected to a continuous 

 mixing process. The onward movement is effected by waves of con- 

 traction which sweep along the muscular coat of the bowel, and con- 

 stitute what is known as peristalsis. The mixing of the material in 

 the intestine is brought about by ring-like or segmental contractions, 

 which are not progressive in character. These movements may be 

 observed in the living animal or person by the aid of Rontgen rays 

 after the administration of a bismuth meal. They can also be observed 

 directly, if the abdomen is opened hi an animal immediately after it 

 has been killed. The movements may be recorded in the living 

 animal by means of a balloon inserted into the lumen of the bowel 

 and connected with a writing tambour; contraction of the intestinal 

 wall compresses the balloon, and air is forced into the tambour, 

 thereby raising the lever. Other experimental methods may also 

 be used. 



The Peristaltic Movements. Any mechanical stimulus, such as 

 pinching the intestine, will set up a peristaltic wave. The normal 

 stimulus is a bolus in the lumen of the gut, and it is for this reason 

 that the indigestible material of vegetable food is of value in promot- 

 ing peristalsis. There are two features characteristic of the peristaltic 

 wave. First, it is preceded by a wave of relaxation which begins below 

 the point of stimulation, the contraction wave itself beginning above 

 that point. Second, it always travels in the aboral direction. If 

 a segment of the intestine be excised and again stitched in position in 

 a reversed direction, the peristaltic waves in the reversed segment will be 

 opposed to those of the rest of the intestine, and partial obstruction to 

 the passage of the intestinal contents will result. Peristalsis still 

 occurs when all connections with the central nervous system have 

 been divided, but it is abolished by painting the gut with nicotine 

 or cocaine. We may conclude, therefore, that it is effected by a local 

 reflex mechanism connected with Auerbach's plexus (the myenteric 

 plexus) in the muscular coat, the stimulus arising from the presence of 

 a bolus in the intestine, and depending upon either the stretching of 

 the intestinal wall or the irritation of nerve endings in the mucous 



