346 DIGESTION. 



by a constant slight contraction under the influence of the 

 spinal cord. 



The peculiar condition of the sphincter, in relation to the 

 nervous system, will be again referred to. The remaining 

 portion of the intestinal canal is under the direct influence 

 of the sympathetic or ganglionic system, and indirectly, or 

 more distantly, is subject to the influence of the brain and 

 spinal cord, which influence appears to be, in some degree, 

 transmitted through the vagus nerve. Experimental irri- 

 tation of the brain or cord produces no evident or constant 

 effect on the movements of the intestines during life ; yet 

 in consequence of certain conditions of the mind, the move- 

 ments are accelerated or retarded ; and in paraplegia the 

 intestines appear after a time much weakened in their 

 power, and costiveness, with a tympanitic condition, ensues. 

 Immediately after death, irritation of both the sympathetic 

 and pneumo-gastric nerves, if not too strong, induces 

 genuine peristaltic movements of the intestines. Violent 

 irritation stops the movements. These stimuli act, no 

 doubt, not directly on the muscular tissue of the intestine, 

 but on the rich ganglionic structure shown by Meissner to 

 exist in the sub-mucous tissue. This regulates and controls 

 the movements, and gives to them their peculiar slow, 

 orderly, rhythmic, and peristaltic character, both naturally, 

 and when artificially excited. 



