MOVEMENTS OF THE SMALL INTESTINE. 377 



but viewed from the duodenal side, the constriction is 

 abrupt, so that regurgitation is generally difficult. 1 



Once in the intestine, the food is propelled along the 

 canal by peculiar movements, which have been called peri- 

 staltic, when their direction is toward the large intestine, and 

 antiperistaltic, when the direction is reversed. These move- 

 ments are of the character peculiar to the unstriped mus- 

 cular fibres; i. &, slow, gradual, the contraction enduring for 

 a certain time, and followed by a correspondingly slow and 

 gradual relaxation. Both the circular and the longitudinal 

 muscular layers participate in these movements. If we care- 

 fully watch this action in the intestines of an animal after 

 the abdomen has been opened, we can sometimes see a gradual 

 constriction produced by the action of the circular fibres at 

 a certain point, which is slowly propagated along the tube, 

 while, at the same time, the longitudinal fibres are alter- 

 nately contracted and relaxed in the same gradual manner, 

 shortening and elongating the tube and facilitating the on- 

 ward passage of its contents. It can readily be appreciated 

 how movements of this kind are capable of propelling the 

 alimentary mass slowly but certainly along the intestinal 

 tract, even when the direction is in opposition to the force of 

 gravity ; and how admirably these movements are calculated 



1 When the stomach is empty, the pylorus is relaxed, so that the bile fre- 

 quently passes in from the duodenum ; but as soon as the food is passed into 

 the stomach by the resophagus, the pylorus becomes firmly closed. It is stated 

 by Magendie (Precis filementaire de Physiologic, Paris, 1836, p. 83), and this 

 view is adopted by some physiologists, that the pylorus allows matters to pass 

 with difficulty from the stomach to the intestine, but that regurgitation from the 

 intestine to the stomach is comparatively easy. This opinion is based upon an 

 experiment of Magendie, in which he showed that air contained in the stomach 

 could not be forced into the intestine by pressure with the hands, while the 

 pressure easily passed air from the duodenum iato the stomach. (Loc. cit.} It 

 must be remembered, however, that the muscular fibres of the pylorus are con- 

 nected with the stomach, and not with the intestine ; and that pressure exerted 

 upon the stomach would cause them to contract, but pressure upon the duodenum 

 would have no such effect. We have already noted that during a quiescent con- 

 dition of the stomach, these fibres are relaxed. 



