204 TEXT-BOOK OF PHYSIOLOGY 



a point two or three centimeters above the anus they form, as stated above, 

 the internal sphincter. 



The mucous membrane of the large intestine possesses neither villi nor 

 valvulae conniventes. It contains a large number of tubules consisting of a 

 basement membrane lined by columnar epithelium. They resemble the 

 follicles of Lieberkuhn. The secretion of these glands is thick and viscid 

 and contains a large quantity of mucin. 



The Movements of the Large Intestine. As a result of the actions of 

 saliva, of gastric, intestinal, and pancreatic juice, and of the bile, the food is 

 disintegrated and liquefied. The nutritive principles, protein, starches, sugars, 

 and fats, undergo chemic changes and are transformed into amino-acids and 

 peptids, dextrose, soap and glycerin, fat acids, under which forms they are 

 absorbed. After the more or less complete digestion and absorption of these 

 nutritive substances the residue of the food, comprising the indigestible and 

 undigested matter, passes out of the small intestine into the large intestine 

 and forms a portion of its contents. This residue consists of the hard parts 

 of the cereals, vegetable seeds, cellulose, etc., the quantity and variety of 

 which depend on the nature of the food. These substances, passing into 

 the large intestine along with the excrementitious matter of the bile, become 

 incorporated with the mucous secretions and assist in the formation of the 

 feces. 



Under the influence of a peristaltic movement similar to that wit- 

 nessed in the small intestine, all this excrementitious matter, deprived by 

 absorption of the excess of its contained water and nutritive material, is 

 gradually carried downward to the sigmoid flexure, where it accumulates 

 prior to its extrusion from the body. The effects of the peristaltic waves are 

 to some extent interfered with by anti-peristaltic or anastaltic waves which, 

 beginning in the transverse colon, run toward and to the cecum. An anti- 

 peristaltic wave occurs in the cat about every fifteen minutes and lasts for 

 about five minutes. The intestinal contents are thereby driven back toward 

 the cecum. The effect is a still further admixture with the secretions and 

 exposure to the absorbing mucosa. There is some evidence also that the 

 anti-peristaltic waves may force some of the liquefied contents through the 

 iieo-colic opening into the small intestine because of the relaxation of the ilio- 

 colic sphincter muscle. It is questionable if this ascending movement is a 

 true peristalsis inasmuch as the advancing contraction is apparently not pre- 

 ceded by an area of inhibition or relaxation. It resembles rather the corre- 

 sponding movement manifested by the small intestine to which the term 

 anastalsis has been given, and is propagated along the muscle coat independ- 

 ently of the myenteric plexus. 



In addition to this anastaltic wave, haustral contractions have been ob- 

 served which resemble the segmentation contractions of the small intestines 

 and which promote, it is believed, the absorption or drawing of water from 

 the intestinal contents. 



The Function of the Large Intestine. The large intestine, by reason 

 of its anatomic relation to the small intestine, serves, as a receptacle for the 

 temporary storage of the indigestible residue of the food together with certain 

 excretions of the intestinal glands both of which have descended from the 

 small intestine. Inasmuch as the contents of the large intestine, in that 

 portion known as the ascending colon are quite liquid, while the contents 



