Digestion. 157 



exists in the lumbar cord — having been liberated by a 

 voluntary act. If this centre be destroyed the anus be- 

 comes flaccid and the rectum remains full, showing that 

 the mechanism which contracts the anus also contracts the 

 rectum. 



After the contents of the bowels have been evacuated 

 the sphincter closes, and in doing so imprisons a portion of 

 the mucus membrane of the bowel, which temporarily 

 remains everted and is then gradually withdrawn. 



Meconium is the dark-green material found in the intes- 

 tines of the foetus. It consists of biliary matters, both 

 acids and pigments, fatty acids, and cholesterin ; whilst the 

 salts of magnesium and calcium, phosphoric and sulphuric 

 acids, sodium chloride, soda, and potash are also found 

 in it. The meconium is the product of liver excretion. 



Nervous Mechanism of the Intestinal Canal. — What we 

 have previously said about the stomach nervous mechanism 

 applies equally to the bowels. Secretion can be excited by 

 chemical, thermal, and other stimuli, the normal irritation 

 being naturally the food passing along the canal. Irrita- 

 tion of the vagus produces no influence on the secretion ; 

 extirpation of the coeliac and mesenteric plexuses causes a 

 profuse secretion ; and in the same way division of the 

 nerves leading to a loop of bowel produces an outpouring 

 of intestinal fluid. The injection of pilocarpine causes a 

 considerable secretion, and powerful contraction of the 

 intestinal walls ; the action of this drug on the horse, and 

 its elective affinity for the salivary, pancreatic, and intestinal 

 glands is very remarkable. 



The intestines contain local ganglia, and these are 

 capable of sustaining the movements of the bowel when 

 all other sources of nerve-supply are cut off"; this is well 

 seen in the movements of the intestines of a recently- 

 destroyed horse. The augmentor fibres from the vagus, 

 and the inhibitory fibres from the sympathetic system, 

 such as are described on p. 141, apply with equal force to 

 the muscular wall of the intestinal canal; it is possible 

 that the two intestinal muscles have a distinct source of 



