666 PHYSIOLOGY OF DIGESTION AND SECRETION. 



of pilocarpin and strychnin. Cannon, in his observations upon cats, 

 found that all movements of the stomach ceased as soon as the 

 animal showed signs of anxiety, rage, or distress. 



Movements of the Intestines. The muscles of the small and 

 the large intestine are arranged in two layers, an outer longitudinal 

 and an inner circular coat, while between these coats and in the 

 submucous coat there are present the nerve-plexuses of Auerbach 

 and Meissner. The general arrangement of muscles and nerves is 

 similar, therefore, to that prevailing in the stomach, and in accor- 

 dance with this we find that the physiological activities exhibited 

 are of much the same character, only, perhaps, not quite so complex. 



Two main forms of intestinal movement have been distinguished, 

 the peristaltic and the pendular or rhythmic. 



Peristalsis. The peristaltic movement consists in a constriction 

 of the walls of the intestine, which, beginning at a certain point, 

 passes downward away from the stomach, from segment to segment, 

 while the parts behind the advancing zone of constriction gradually 

 relax. The evident effect of such a movement is to push onward the 

 contents of the intestines in the direction of the movement. 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 running 

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

 peristalsis 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 obstructio n (Cannon) , and Grutzner * 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 conditions. The peristaltic 

 wave normally passes downward, and that this direction of move- 

 ment is dependent upon some definite arrangement in the intestinal 

 walls is shown by the experiments of Mali f 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 ex- 

 amined 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. 



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

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



