MOVEMENTS OF THE SMALL INTESTINE. 285 



Disregarding slight variations in this table, which might be accidental, it may be 

 stated, in general terms, that the bile commences to increase in quantity immediately 

 after eating ; that its flow is at its maximum from the second to the eighth hour, during 

 which time the quantity does not vary to any great extent ; after the eighth hour it 

 begins to diminish, and, from the twelfth hour to the time of feeding, it is at is minimum. 



Although it has been pretty satisfactorily demonstrated that the presence of the bile 

 in the small intestine is necessary to proper digestion and even essential to life, and 

 although the variations in the flow of bile with digestion are now well established, it 

 must be confessed that we have scarcely any definite information concerning the mode 

 of action of the bile in intestinal digestion and absorption. Nearly all that we can say on 

 this point is that its action seems to be auxiliary to that of the other digestive fluids. 



Movements of the Small Intestine. 



By the contractions of the muscular coat of the small intestine, the alimentary mass 

 is made to pass along the canal, sometimes in one direction and sometimes in another ; 

 the general tendency, however, being toward the c^cum. The partially-digested matters 

 which pass out at the pylorus are prevented from returning to the stomach by the pecul- 

 iar arrangement of the fibres which constitute the pyloric muscle. The passage from 

 the stomach to the intestine, as we have seen, becomes constricted gradually, so that 

 food of the proper consistence finds its way easily into the duodenum ; but, viewed 

 from the .duodenal side, the constriction is abrupt, so that regurgitation is generally 

 difficult. 



Once in the intestine, the food is propelled along the canal by peculiar move- 

 ments, which have been called peristaltic, when its direction is toward the large 

 intestine, and antiperistaltic, when the direction is reversed. These movements are 

 of the character peculiar to the unstriped muscular fibres ; viz., slow, gradual, the 

 contraction enduring for a certain time and being followed by a correspondingly slow 

 and gradual relaxation. Both the circular and the longitudinal muscular layers par- 

 ticipate in these movements. If we carefully watch this action in the intestines of 

 an animal after the abdomen has been opened, we can sometimes see a gradual constric- 

 tion 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 alternate- 

 ly contracted and relaxed in the same gradual manner, shortening and elongating the 

 tube and facilitating the onward 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 we can see how admirably these movements are calculated to thorough- 

 ly incorporate the food with the digestive fluids and to expose those parts which have 

 been completely liquefied to the absorbent action of the mucous membrane. 



Although the mechanism of the propulsive movements of the intestine may be studied 

 in living animals after opening the abdomen, or, better still, in animals just killed, the 

 movements thus observed do not entirely correspond with those which take place under 

 natural conditions. In vivisections, no movements are observed at first ; but, soon after 

 exposure of the parts, nearly the whole intestine moves like a mass of worms. In the 

 normal process of digestion, the movements are never so general or so active ; they take 

 place more regularly and consecutively in those portions in which the contents are most 

 abundant, and the movements are generally intermittent, being interrupted by long inter- 

 vals of repose. In Prof. Busch's case of intestinal fistula, there existed a large ventral 

 hernia, the coverings of which were so thin that the peristaltic movements could be readily 

 observed. In this case, the general character of the movements corresponded with what 

 has been observed in the inferior animals. It was noted that the movements were not 

 continuous, and that there were often intervals of rest for more than a quarter of an hour. 



