158 A Manual of Veterinary Physiology. 



supply : in the same way the opposite action of the vagus 

 and sympathetic on the bloodvessels of the stomach are 

 observed to apply to the intestinal walls. 



Practically we know that bulk is necessary for intestinal 

 digestion, a horse cannot be kept in condition on con- 

 centrated food ; bulk promotes intestinal peristalsis, and 

 probably the presence of gases in the intestine within 

 certain limits also has an influence in this direction. 



When the blood-supply to the bowel is cut off, increased 

 peristaltic action occurs ; this is the probable explanation 

 of the movements seen in bowels removed from an animal 

 recently destroyed, and is possibly the cause of the expul- 

 sion of the contents of the rectum when life is suddenly 

 and violently taken away. 



The nervous mechanisms employed in defsecation are 

 described on p. 156. 



