480 FJECES. [BOOK n. 



when the bile is cut off from the intestine shews that the bile- 

 pigment is at least the mother of the faecal pigment ; and a 

 special pigment, which has been isolated and called stercobilin, is 

 said to be identical with the substance called urobilin, which may 

 be formed from bilirubin. As other special constituents of the 

 faeces may be mentioned excretin, a somewhat complex nitrogenous 

 body, whose exact chemical nature is at present uncertain, and 

 skatol (C 9 H 9 N), a nitrogenous body which like indol is derived 

 from the decomposition of proteids by means of micro-organisms, 

 and which is the chief cause of the faecal odour, since only a small 

 quantity of indol remains in the faeces. These odoriferous bodies 

 are derived directly from the food; at the same time it is quite 

 possible that other specific odoriferous substances may be secreted 

 directly from the intestinal wall, especially from that of the large 

 intestine. 



