vi INTESTINE AS AN ORGAN OF EXCRETION 367 



(enterokinase). It did, however, contain an amylolytic ferment 

 and Colmheim's erepsin. 



While nothing definite is known, we are justified in assuming 

 that along with digestive functions, the fermentation and putre- 

 faction of substances accumulated in the large intestine, and the 

 absorption of water and of certain soluble products, the large 

 intestine also excretes the waste products of the body, which 

 mingle with its contents, and increase the mass of the faeces. 



O 



From these products we must distinguish the mucus, which is by 

 a long way the chief constituent of the secretion from the epi- 

 thelial cells of the large intestine, both of the superficial cells and of 

 those which line the numerous crypts. This mucous secretion has, 

 as we showed elsewhere, the specific function of lubricating the 

 external surface of the faecal balls, so as to facilitate their 

 expulsion by the anus. 



In proportion as the faecal masses are condensed by the active 

 absorption that takes place in the large bowel, and assume a 

 pasty, or more or less hard, consistency, absorption of the toxic 

 substances contained in the faeces becomes more and more 

 difficult. The phenomena of auto-intoxication are thus avoided, 

 because under normal conditions the toxic constituents of the 

 faeces are so slowly absorbed, that they are eliminated by the 

 urine as fast as absorption takes place. As soon, therefore, as 

 the faeces have attained a proper consistency, absorption ceases 

 entirely, and the toxic matters are expelled with the faeces in 

 defaecation (Bouchard). 



VII. In man the Large Intestine with its three parts (caecum, 

 colon, rectum} is 1'50-1'SO m. long, i.e. about one-fifth of the whole 

 length of the intestinal canal. Its diameter is greater than that 

 of the small intestine, and varies in the different parts from 5 to 

 12-5 cm. The caecum has the largest diameter, which diminishes 

 gradually in the three segments of the colon (ascending, transverse, 

 sigmoid), and in the rectum, except that near the end of the latter 

 there is a well-marked dilatation (rectal ampulla}. Like the 

 stomach and small intestine, it has four coats (serous, muscular, 

 subniucous, and mucous), but the greater part of the large intestine 

 (caecum, colon) differs very much from the even, cylindrical form 

 of the small intestine, its surface being thrown into numerous 

 sacculi. This comes from the arrangement of the longitudinal 

 muscle fibres, which thicken in the form of three strong bands 

 (sometimes known as the ligamenta coli} and are shorter than the 

 part of the tube through which they run, so that it exhibits three 

 series of saccular dilatations, separated by constrictions ; these 

 correspond inside the gut with three more or less prominent 

 ridges composed of all the coats, by which the canal is thrown 

 into sacculi (Fig. 103). This arrangement is certainly intended 

 to delay the advance of the faecal mass along the large intestine, 



