DIGESTION 359 



general all vegetable structures chiefly composed of cellulose. 

 They are coloured with a pigment, stercobilin, derived from 

 the bile pigments. Stercobilin is identical with ' febrile ' 

 urobilin, with the urobilin which forms a common, though not 

 an invariable, constituent of bile itself, and probably with the 

 urobilin of normal urine. No bilirubin or biliverdin occurs 

 in normal faeces, although pathologically they may be present. 

 The dark colour of the faeces with a meat diet is due to 

 haematin and sulphide of iron, the latter being formed by 

 the action of the sulphuretted hydrogen which is constantly 

 present in the large intestine on the organic compounds 

 of iron contained in the food or in the secretions of the 

 .alimentary canal. A small amount of altered bile acids and 

 their products is also found ; and in respect to these, and to 

 the altered pigments, bile is an excretion. And although its 

 important function in digestion, and the fact that the greater 

 part of the bile salts is reabsorbed,* show that in the adult 

 it is very far from being solely a waste product, the equally 

 cogent fact, that the intestine of the new-born child is filled 

 with what is practically concentrated bile (meconium), proves 

 that it is just as far from being purely a digestive juice. 

 Skatol and other bodies, formed by putrefactive changes in 

 the proteids of the food, are also present in the faeces, and 

 are responsible for the faecal odour. Masses of bacteria are 

 invariably present. Of the inorganic substances in faeces 

 the numerous crystals of triple phosphate are the most 

 characteristic. When the diet is too large, or contains too 

 much of a particular kind of food, a considerable quantity 

 of digestible material may be found in the faeces, e.g., 

 muscular fibres and fat. But it should be remembered that 

 under all circumstances the composition of the faeces differs 

 from that of the food. The intestinal contribution is always 

 an important one, although relatively more important with 

 a flesh than with a vegetable diet. 



* Stadelmann concludes from an elaborate review of previous work 

 and numerous fresh experiments that a circulation of the bile-acids (/.<?., 

 an absorption from and re-excretion into the intestine) is proved ; that a 

 circulation of the bile-pigments is probable ; but that a circulation of the 

 vcholesterin of the bile does not take place at all. 



