424 DIGESTION 



intestine, the faeces consist of indigestible remnants of the food, such 

 as elastic fibres, spiral vessels of plants, and in general all vegetable 

 structures chiefly composed of cellulose. They are coloured wich a 

 pigment, stercobilin, derived from the bile -pigments. Stercobilin 

 is identical with urobilin, which forms a common, though not an 



Fig. 170. Effect of Extract of Faeces on Blood-Pressure. The extract was injected 

 at 2. Time-trace, seconds. 



invariable, constituent of bile itself. A portion of it is absorbed by 

 the intestine and then excreted in the urine, the urobilin in which 

 is often much increased in fever (' febrile ' urobilin). 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 entrance into the upper instead of the lower end 

 of the intestine, the ascertained importance of its function in diges- 

 tion, 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 

 proteins of the food, are also present in the faeces, and are responsible 

 for the faecal odour. Masses of bacteria are invariably present, and 

 often make up a very considerable proportion of the total faecal 



