BILE 75 



juice to have full play. Bile is a solvent of fatty acids, and assists 

 the absorption of fat (see p. 80). 



THE FATE OF THE BILIARY CONSTITTJENTS 



We have seen that fistula bile is poor in sohds as compared with 

 normal bile, and that this is explained on the supposition that the 

 normal bile circulation is not occmTing — the hver cannot excrete 

 what it does not receive back from the intestine. Schiflf was the first 

 to show that if the bile is led back into the duodenum, or even if the 

 animal is fed on bile, the percentage of sohds in the bile excreted is at 

 once raised. It is on these expeiiments that the theory of a bile 

 circtdation is mainly founded. The bUe circulation relates, however, 

 chiefly, if not entirely, to the bile salts : they are found but sparingly 

 in the faeces ; they are only represented to a shght extent in the urine : 

 lence it is calculated that seven-eighths of them are re-absorbed from 

 Aie intestine. Small quantities of cholahc acid, taurine, and glycocine 

 are found in the faeces ; the greater paiii of these products of the decom- 

 position of the bile salts is taken by the portal vein to the liver, where 

 they are once more sjTithetised into the bile salts. Some of the taurine is 

 absorbed and excreted as tauro-carbamic acid (C2H4NHCO.NH2HSO3) 

 in the urine. Some of the absorbed glycocine may be excreted as urea 

 or uric acid. The cholesterin and mucus are found in the faeces ; the 

 pigment is changed into stercobilin, a substance like hydrobilirubin. 

 Some of the stercobihn is absorbed, and leaves the body as the urinary 

 pigment, urobihn. 



THE F-ECES 



The faeces are alkaline in reaction, and contain the following sub- 

 stances : — 



1. Water : in health from 68 to 82 per cent. ; in diarrhoea it is 

 more abundant stiU. 



2. Undigested food ; that is, if food is taken in excess, some escapes 

 the action of the digestive juices. On a moderate diet unaltered 

 proteid is never found. 



3. Indigestible constituents of the food : cellulose, keratin, mucin, 

 chlorophyll, gums, resins, cholesterin. 



4. Constituents digestible with difficulty : uncooked starch, ten- 

 dons, elastin, various phosphates, and other salts of the alkaline earths. 



5. Products of decomposition of the food : indole, skatole, phenol, 

 acids such as fatty acids, lactic acid, &c. ; haematin from haemoglobin ; 

 insoluble soaps like those of calcium and magnesium. 



