MOVEMENTS OF THE ALIMENTARY CANAL. 727 



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. 



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. The force of the contraction 

 as measured by Cashf in the dog's intestine is very small. A 

 weight of five to eight grams was sufficient to check the onward 

 movement of the substance in the intestine and to set up violent, 

 colicy contractions which caused the animal evident uneasiness. 

 The time required for the passage of food through the small in- 

 testine must vary with its amount and character. From obser- 

 vations made upon man with the x-ray, Hertz estimates that on 

 the average it requires about 4f hours. After a meal, therefore, 

 we may imagine that at about the time the stomach has finished 

 discharging its contents into the duodenum the first portions 

 have reached the ileocecal valve. That is to say, a column of 

 food, broken into separate segments, stretches at one time practi- 

 cally along the whole length of the small intestine. 



Mechanism of the Peristaltic Movement. The means by which 

 the peristaltic movement makes its orderly forward progression 

 have not been determined beyond question. The simplest explana- 



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



t "Proceedings of the Royal Society," London, 41, 1887. 



