28 



DIGESTION 



muscles are active. By virtue of the latter, small waves arise in the intestinal 

 wall, which are propagated rather rapidly (2-5 cm. per second), usually from 

 above downward. 



(2) In separate parts of the intestine powerful contractions occur which 

 proceed much more slowly than the above-mentioned small waves, but like 

 them from above downward. These are the true peristaltic movements. In 

 the propagation of these contractions the intestine is always dilated just 



below the place which at that 



moment is contracted. 



The peristaltic movements may 

 be produced on an e-nervated intes- 

 tine by a weak mechanical stimu- 

 lus of the outer surface, or bet- 

 ter still by the introduction of a 

 balloon into the intestine. Every 

 such stimulus excites the section 

 lying above the point at which it 

 is applied and relaxes that lying 

 immediately below (Bayliss and 





? v 



'oOOOOQcT 



FIG. 116. Schema to illustrate the rhythmical 

 segmentation of the small intestine, after Can- 

 non. 1, the contents of the intestine unseg- 

 mented; 2, the contents constricted into 

 separate masses ; 3, the next phase, the origi- 

 nal segments are split in half by new constric- 

 tions and become fused into new masses, as a 

 and b into c ; 4, the first segmentation restored. 



Starling). 



Peristalsis in the intestine is 

 therefore a tolerably complicated 



phenomenon which calls for a definite, regular coordination of different portions 

 of the intestine, and in all probability requires for its excitation the participa- 

 tion of a nervous mechanism. Since this can be observed in all its regularity 

 both in an exsected intestine and in the intestine deprived of extrinsic nerves, 

 the mechanism concerned must lie within the intestinal wall itself, and we have 

 probably to regard the plexus myentericus as that mechanism. 



Magnus is authority for the statement that the spontaneous movements con- 

 tinue unchanged in their character in surviving portions of the intestine, or in 

 those preserved in Ringer's solution, after removal of the submucosa and of 

 Meissner's plexus. But separation of the circular layers from Auerbuch's plexus 

 stops their movements, whereas the longitudinal muscles left in connection with 

 this plexus continue as before to contract. From these results it would appear 

 that all the automatic movements of the intestine depend upon the action of 

 Auerbuch's plexus. 



The intestinal movements are regulated in many ways by the central 

 nervous system; and we can say further that the small intestine receives its 

 efferent nerves partly through the vagus and partly through the splanchnic. 

 But with regard to the action of these nerves, until very recently there was 

 absolutely no unanimity of opinion. Indeed one may say without exagger- 

 ation that every conceivable possibility has been represented by the different 

 authors. 



However, most authors now agree that the splanchnics contain inhibiting 

 fibers for the intestine (Pniiger, 1857). If the abdomen of a fasting dog, 

 having the splanchnics still intact, be opened, the above-mentioned contrac- 

 tions are not observed the intestine is perfectly quiescent. A local stimulus 

 is either entirely without effect or it produces only a circumscribed contrac- 



