INTESTINAL MOV MM MNTS. 



127 



chiefly depends on the mechanical effect, but also is probably 

 intimately related to the interference with the blood supply con- 

 sequent on the pressure exerted by the constricting baud. Pro- 

 longed over-work often induces immobility of the intestinal wall, 

 and hence we find the purging and vomiting, which accompany 

 a temporary hernial constriction, followed by inability of the 

 intestine to propel its contents. These points have also been 

 proved by results of experiments on the lower animals. 



The movements of the large intestines are the same as the small, 

 but not so obvious, owing to the modified sacculated shape of this 



FIG. 56. 



Diagram of a Longitudinal Section of the Wall of the Small Intestine. a. Villi. b. 

 Lieberktthn's glands, c. Muscularis mucosse, below which lies Meissner's nerve plexus. 

 d. Connective tissue in which many blood and lymph vessels lie. . Circular muscle 

 fibres cut across, with Auerbach's nerve plexus below. /. Longitudinal muscle fibres. 

 g. Serous coat. 



part of the alimentary canal. The contractions of the colon begin 

 at the ileo-caecal valve where the peristaltic wave of the ileum 

 ceases. The normal intestinal motions thus pass in an almost 

 uninterrupted wave from the pylorus to the end of the gut, but 

 when special sources of irritation exist, a wave may originate in 

 almost any intermediate part of the intestine. A reversed "anti- 

 peristaltic motion," as it is called, only occurs as a result of some 

 intense local stimulation, such as the strangulation of a hernia, etc. 

 The motion produced by the substances contained in the intes- 

 tine depends on their character. The solid parts excite more 



