MOVEMENTS OF THE ALIMENTARY CANAL. 645 



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 running 

 in the opposite direction that is, toward the stomach. Anti- 

 peristalsis is said not to occur under normal conditions; it has been 

 observed sometimes in isolated pieces of intestine or in the exposed 

 intestine of living animals when stimulated artificially, and Griitz- 

 ner* reports a number of curious experiments which seem to show 

 that substances such as hairs, animal charcoal, etc., introduced into 

 the rectum may travel upward to the stomach under certain con- 

 ditions. The peristaltic wave normally passes downward, and that 

 this direction of movement is dependent upon some definite ar- 

 rangement in the intestinal walls is shown by the experiments of 

 Mallf 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 gradually 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. 



The peristaltic movements of the intestines may be observed 

 upon living animals when the abdomen is opened. If the operation 

 is made in the air and the intestines are exposed to its influence, or 

 if the conditions of temperature and circulation are otherwise 

 disturbed, the movements observed are often violent and irregular. 

 The peristalsis runs rapidly along the intestines and may pass over 

 the whole length in about a minute; at the same time the con- 

 traction of the longitudinal muscles gives the bowels a peculiar 

 writhing movement. Movements of this kind are evidently 

 abnormal, and only occur in the body under the strong stimulation 

 of pathological conditions. Normal peristalsis, the object of which 

 is to move the food slowly along the alimentary tract, is quite a 

 different affair. Observers all agree that the wave of contraction 

 is gentle and progresses slowly, although at different rates perhaps 

 in different parts of the intestine. According to Bayliss and Star- 

 ling,:]: the peristaltic movement is a complicated reflex through the 

 intrinsic ganglia. When the intestine is stimulated by a bolus 

 placed within its cavity, the musculature above the point stimulated 

 is excited, while that below is inhibited. In accordance with this 

 law they find that in peristalsis the advancing wave of constriction 



*" Deutsche medicinische Wochenschrift, " No. 48, 1894. 

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

 % "Journal of Physiology," 24, 99, 1899. 



