390 DIGESTION. 



of the colon. In the lower fourth, the fibrous tissue by which 

 the lining membrane is united to the subjacent muscular 

 coat is loose, and the membrane, when the canal is empty, is 

 thrown into a great number of irregular folds. At the site 

 of the internal sphincter, five or six little semilunar valves 

 have been observed with their concavities directed toward the 

 colon. These form an irregular festooned line which surrounds 

 the canal ; their folds, however, are small and have no tenden- 

 cy to obstruct the passage of faecal matters. The simple folli- 

 cles are particularly abundant in the rectum, and the mem- 

 brane is constantly covered with a thin coating of mucus. 

 Another peculiarity to be noted in the mucous membrane 

 of the lower portions of the rectum, is its great vascularity ; 

 the veins, especially, being very numerous. 



Finally, the rectum terminates in the anus, a button-hole 

 orifice, situated a little in front of the coccyx, which is kept 

 closed and somewhat retracted, except during the passage of 

 the faeces, by the powerful external sphincter. This muscle 

 is composed entirely of red or striated fibres, which are ar- 

 ranged in the form of an ellipse, its long diameter being 

 antero-posterior. 



It is now almost universally admitted that the digestion of 

 all classes of alimentary substances is completed either in the 

 stomach or the small intestine, and that the mucous membrane 

 of the large intestine does not secrete a fluid endowed with 

 any well marked digestive properties. The simple follicles, 

 the closed follicles, and the utricular glands, produce a glairy 

 mucus, which, as far as we know, serves merely to lubricate 

 the canal. This has never been obtained in sufficient quan- 

 tity to admit of any accurate investigation into its properties. 1 



1 It is now pretty generally conceded by practical physicians that it is pos- 

 sible to support the vital powers for a time by nutrient matters introduced into 

 the large intestine by injection. As can readily be .understood, there are ob- 

 stacles in the employment of this method of alimentation which render its ap- 

 plication difficult, if not impossible, in many cases ; but instances have been 

 reported in which it has been used for a long time with complete success. One 



