236 DIGESTION. [CHAP. xxv. 



The mucous membrane of the c&cum, and of the whole large 

 intestine, is distinguished by the complete absence of villi ; by the 

 presence of Lieberkiihn's follicles, and of solitary glands of large 

 size, which are numerous in the vermiform appendix, as well as 

 in the coecum itself; and by the folds which form the partitions 

 between the cells of the colon, as well as by the valvular folds of 

 the rectum. 



Movements of the Intestines. The substances which enter the 

 intestinal canal from the stomach, are moved onwards by means of 

 what is called the peristaltic, or the vermicular action of its muscu- 

 lar coat. 



This action of the intestines is very conspicuous in animals 

 opened immediately after death; under these circumstances it is pro- 

 bably in an exaggerated state owing to the stimulus created by the 

 entrance of cold air into the abdomen. It may be displayed in a 

 highly active state by subjecting the intestinal canal of an animal 

 just dead, to the influence of the magneto-electric machine, by the 

 successive shocks of which this action becomes greatly increased in 

 intensity and rapidity, though not altered in character. 



In dogs and cats, in which we have most frequently observed the 

 peristaltic action, it seems to commence at the pyloric third of the 

 stomach, whence successive waves of contraction and relaxation 

 (the former being instantly succeeded by the latter) are propa- 

 gated throughout the entire length of the small and large intes- 

 tines. The advance of the waves is always downwards. In ex- 

 amining a portion of intestine at the moment of its contraction, 

 we perceive a dilatation above it as well as below it ; the latter 

 being produced by the protrusion into it of the contents of the 

 now contracted portion of intestine ; the former by the relaxation 

 of a previously contracted portion. The rapid succession of these 

 contractions and relaxations gives to the movements of the intestines 

 the appearance of the writhings of a worm, whence they are dis- 

 tinguished by the appellation vermicular. Sometimes we have 

 opportunities of observing these movements during life in man, in 

 cases of extreme attenuation of the abdominal parietes; or in 

 cases where, from some great obstruction in the course of the 

 alimentary canal, the peristaltic action is very much increased in 

 intensity above the seat of the obstruction ; or in wounds of the 

 abdomen ; or during surgical operations. 



There are certain facts which justify the supposition that this 

 vermicular action has a proper rate of speed in each individual, and 



