MOVEMENTS OF THE ALIMENTARY CANAL. 723 



their afferent and efferent connections. When a bohis is inserted 

 into the intestine at any point its effect upon the nerve-fibers is 

 such as to cause a reflex contraction of the muscle above the bolus, 

 that is, toward the stomach, and a reflex inhibition or dilatation 

 below. They speak of this definite relationship as the Imv of the 

 intestine; it is described also under the name myenteric reflex. It 

 is obvious that the circular layer of muscles is chiefly involved in 

 peristalsis, since constriction can only be produced by contraction 

 of this layer. To what extent the longitudinal muscles enter into 

 the movement is not definitely determined. The term "anti- 

 peristalsis" is used to describe the same form of movement run- 

 ning in the opposite direction — that is, toward the stomach. 

 Antiperistalsis is said not to occur under normal conditions; it has 

 been observed in isolated pieces of intestine or in the exposed 

 intestine of living animals when stimulated artificially or after 

 complete intestinal obstruction (Cannon). The peristaltic wave 

 normally passes downward, and that this direction of movement 

 is dependent upon some definite arrangement in the intestinal 

 walls is shown by the experiments of Mall* upon reversal of the 

 intestines. In these experiments a portion of the small intestine 

 was resected, turned around, and sutured in place again, so that in 

 this piece what was the lower end became the upper end. In those 

 animals that made a good recovery the nutritive condition gradu- 

 ally became very serious, and when the animals were killed and 

 examined it was found that there was an accumulation of food at 

 the stomach end of the reversed piece of intestine, and that this 

 region showed marked dilatation. 



According to the observations made upon man by means of 

 the x-TSiy the normal peristaltic waves run only for a few inches 

 from the point at which they start, f and their course is quite 

 rapid. After the cessation of the peristaltic wave there is a period 

 of rest during which the column of food undergoes segmentation 

 by the action of the localized rhythmic contractions described in 

 the next paragraph. The general story of the movement of the 

 food is, therefore, as follows: The stomach discharges food at 

 intervals into the intestine, and each such charge makes its passage 

 along the intestine in a series of short runs, due to the peristaltic 

 contractions, each run moving the column on for a few inches. 

 The first column or charge of food reaches the ileocecal sphincter 

 in four to four and a half hours on the average, about the time 

 that the last portions of food are leaving the stomach. Hurst 

 states that in the last few inches of the ileum the food accumulates 



* "Johns Hopkins Hospital Reports," 1, 93, 1896. 



t Hurst, "Physiology of the Intestinal Movements," etc., in "Constipa- 

 tion and Allied Intestinal Disorders," London, 1919. 



