94 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



chiefly to the fact that by increasing absorption it lessens the amount 

 of putrescible matter in the bowel. 



When the bile meets the chyme the turbidity of the latter is 

 increased, owing to the precipitation of unpeptonised protein. This is 

 an action due to the bile salts, and it has been surmised that this con- 

 version of the chyme into a more viscid mass is to hinder somewhat 

 its progress through the intestines : it clings to the intestinal wall, 

 thus allowing absorption to take place. The neutralisation of the acid 

 gastric juice by the bile also allows the alkalinity of the pancreatic 

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

 the absorption of fat. 



THE FATE OF THE BILIARY CONSTITUENTS 



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

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

 normal bile circulation is not occurring the liver cannot excrete 

 what it does not receive back from the intestine. Schiff 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 solids in the bile excreted is 

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

 circulation is mainly founded. The bile 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 slight extent in the urine ; 

 hence it is calculated that seven-eighths of them are reabsorbed from 

 the intestine. Small quantities of cholalic acid, taurine, and glycine 

 are found in the faeces ; the greater part of these products of the 

 decomposition of the bile salts is taken by the portal vein to the 

 liver, where they are once more synthesised into the bile salts. 

 Some of the taurine is absorbed and excreted as tauro-carbamic 

 acid (C 2 H 4 NHCO.NH 2 HS0 3 ) in the urine. Some of the absorbed 

 glycine may be excreted as urea. The cholesterin and mucus are 

 found in the faeces ; the pigment is changed into stercobilin, a sub- 

 stance like hydrobilirubin. Some of the stercobilin is absorbed, and 

 leaves the body as the urinary pigment, urobilin. 



THE FJECES 



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 still. 



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



