310 A MANUAL OF PHYSIOLOGY 



inhibitory fibres for the stomach, and it is only when these are 

 intact that complete reflex inhibition of the organ can be 

 obtained in the rabbit (Auer). The gastric movements are not 

 permanently affected by section of these nerves alone, or even by 

 simultaneous section of the splanchnics and the gastric branches 

 of the vagi. But if the vagi are cut while the splanchnics remain 

 intact, the peristalsis of the stomach is weakened, its onset 

 delayed, and the proper emptying of the viscus through the 

 pylorus interfered with. In all probability these results are due 

 to the uncontrolled action of the inhibitory fibres. The splanch- 

 nics have a special relation to the ileo-colic sphincter, which 

 closes when they are stimulated, and becomes insufficient when 

 they are cut. The vagus does not affect it. 



The lower part of the large intestine is influenced by the sacral 

 nerves (second, third, and fourth sacral in the rabbit), and by certain 

 lumbar nerves, in the same way as the higher parts of the alimentary 

 canal, and particularly the small intestine, are influenced by the 

 vagus and the splanchnics. Stimulation of these sacral nerves 

 within the spinal canal, or of the pelvic nerves (nervi erigentes) into 

 which they pass, causes contraction of the parts of the large intes- 

 tine concerned in defaecation that is, in the dog, of the whole colon, 

 with the exception of the caecum ; in the cat, of the distal two-thirds 

 of the colon. The colon first undergoes rapicfc shortening due to 

 the contraction of the longitudinal fibres and the recto-coccygeus 

 muscle. After a few seconds this is followed by contraction of the 

 circular fibres, beginning at the lower limit of the region in which 

 antiperistalsis can occur, and spreading downwards, so as to empty 

 the portion of the bowel involved in the contraction. This is a very 

 close imitation of what occurs in natural defaecation. In man the 

 parts involved in these movements are probably the sigmoid flexure 

 and rectum. In addition to these characteristic motor effects on the 

 lower part of the large intestine, stimulation of the pelvic nerves 

 causes an increase in the antiperistalsis of its upper portions. Stimu- 

 lation of the lumbar nerves or of the portions of the sympathetic 

 into which their visceral fibres pass (lumbar sympathetic chain from 

 second to sixth ganglia, or the rami from it to the inferior mesenteric 

 ganglia) causes inhibition of the movements of the caecum and the 

 whole colon, including the antiperistaltic movements. 



Excitation of the sacral nerves initiates or increases the contraction 

 of both coats of the portions of the large intestine on which they act, 

 excitation of the lumbar nerves inhibits both. And in the small 

 intestine the same law holds good ; the two coats are contracted 

 together by the action of the vagus or inhibited together by that of 

 the splanchnics. With the establishment of these facts, the theory 

 that the same nerve which causes contraction of the circular coat in 

 all tubes whose walls are made up of two layers of muscle also con- 

 tains fibres that bring about inhibition of the longitudinal coat, and 

 vice versa, falls to the ground. It was suggested that in this way 

 antagonism between the two coats was prevented. 



Defsecation is partly a voluntary and partly a reflex act. 

 But in the infant the voluntary control has not yet been de- 

 veloped ; in the adult it may be lost by disease ; in an animal 



