320 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



anatomical courses of these fibres are insufficiently known, but there seems to 

 be no question as to the existence of the two physiological varieties. Through 

 their activity, without doubt, the movements of the stomach may be regu- 

 lated, favorably or unfavorably, by conditions directly or indirectly affect- 

 ing the central nervous system. Wertheimer 1 has shown experimentally that 

 stimulation of the central end of the sciatic or the vagus nerve may cause 

 reflex inhibition of the tonus of the stomach, and Doyon 2 has confirmed this 

 result in cases where the movements and tonicity of the stomach were first 

 increased by the action of pilocarpin and strychnin. It must be borne in 

 mind, however, that the action of these extrinsic fibres under normal conditions 

 is probably only to regulate the movements of the stomach. As we have 

 seen, even the extirpated stomach under proper conditions seems to execute 

 movements of the normal type. Normally the movements are provoked by a 

 stimulus of some kind, usually the presence of food material in the interior 

 of the stomach. How the stimulus acts in this case, whether directly upon the 

 muscle-fibres or indirectly through the intrinsic ganglia of the stomach, has 

 not been determined, and the evidence for either view is so insufficient that a 

 discussion of the matter at this time would scarcely be profitable. We must 

 wait for more complete investigations upon the physiology as well as the his- 

 tology of the muscle- and nerve-tissue in this and in other visceral organs 

 constructed on the same type. 



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, there- 

 fore, to that prevailing in the stomach, and in accordance with this we find that 

 the physiological activities exhibited are of much the same character, only, per- 

 haps, not quite so complex. 



Forms of Movement. Two main forms of intestinal movement have been 

 distinguished, the peristaltic and the pendular. 



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 

 would be 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 usually said not to occur under normal conditions ; it has 

 been observed sometimes in isolated pieces of intestine or in the exposed intes- 



1 Archives de Physiologic normale et pathologique, 1892, p. 379. 2 Ibid., 1895, p. 374. 



