METABOLISM 253 



cellulose, and vegetal gums. Then there are residues from the bile: 

 stercobilin (similar to or identical with urobilin and hydrobilirubin), 

 the product of the unabsorbed bile-pigments, and bile-salts likewise 

 for some reason unabsorbed from the colon. Cholesterin is always 

 present, as the refuse of the hepatic metabolism, as well as lecithin. The 

 antiseptic mucin from the goblet-cells of the colon and detritus from 

 the whole length of the alimentary canal's mucosa are never absent. 

 Bacterial putrefaction, active despite the antiseptic powers of the colon's 

 mucus, contributes the tyrosin and its derivatives (skatol, etc.) already 

 noted, besides various cortiplex organic and fatty acids and insoluble 

 soaps. Then there is a substance unfortunately named secretin whose 

 empirical formula is said to be C 20 H 36 O, and which has not been found 

 outside of human feces. (This has nothing to do with the secretin 

 internally secreted by the duodenal wall.) There are also many soluble 

 and insoluble salts of the chief organic metals, calcium, sodium, potas- 

 sium, magnesium, and iron. 



Of the above fecal components, water, stercobilin, the bile-salts, 

 cholesterin, lecithin, mucin, and most likely secretin represent in one way 

 and place or other the katabolism of the tissues, but largely in a manner 

 chemistry cannot at present explain in detail. Of the total three liters or 

 so of water daily excreted, about 150 c.c. (or more on vegetal diet) pass 

 out in the feces; this is about 5 per cent. Stercobilin, the name of the 

 reduced bilirubin of the rectum, represents the iron and the proteid 

 katabolism in the liver, as do, and more especially, the bile-salts. These 

 latter contain nitrogen and some of them also sulphur, but no iron. 

 Both of these hepatic products (pigments and salts) probably have, to 

 some extent at least, a "circulation," being absorbed from the colon 

 into the blood, the pigment being then made over into the hematin of 

 new erythrocytes and the bile-acids entering into anabolic process even 

 less understood, thus saving much constructive energy and material. 

 The cholesterin and lecithin are apparently universal katabolic waste 

 from protoplasm. The mucin, as is well-known, consists of the actual 

 bodies of broken-down epithelium, and represents, therefore, as found in 

 the feces, but a minimum of katabolic change. 



