534 THE LIVES [CIL XXXV. 



alkali is treated with sodium amalgam or allowed to putrefy, a 

 brownish pigment, which is a reduction product, is formed called 

 hydrobilirubin, C 32 H 40 ]Sr 4 7 . It shows a dark absorption band 

 between I and F, and a fainter band in the region of the D line. 



This substance is interesting because a similar substance is formed 

 from the bile pigment by reduction processes in the intestine, and 

 constitutes stercobilin, the pigment of the faeces. Some of this is 

 absorbed and ultimately leaves the body in the urine as one of its 

 pigments called urobilin. A small quantity of urobilin is sometimes 

 found preformed in the bile. The identity of urobilin and stercobilin 

 has been frequently disputed, but the recent work of Garrod and 

 Hopkins has confirmed the old statement that they are the same 

 substance with different names. Hydrobilirubin differs from urobilin 

 in containing more nitrogen (9*2 instead of 4*1 per cent.). 



Cholesterin. Small quantities of this substance are found in 

 normal bile. It may occur in excess, and form the concretions 

 known as gall-stones, which are usually more or less tinged with 

 bilirubin. Its properties and reactions are described on p. 435. 



The Uses of Bile. Bile is doubtless, to a certain extent, 

 excretory. Some state that it has a slight action on fats and carbo- 

 hydrates, but its principal action is as a coadjutor to the pancreatic 

 juice (especially in the digestion of fat). In some animals it has a 

 feeble diastatic power. 



Bile is said to be a natural antiseptic, lessening the putrefactive 

 processes in the intestine. This is very doubtful. Though the bile 

 salts are weak antiseptics, the bile itself is readily putrescible, and 

 the power it has of diminishing putrescence in the intestine is due 

 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 

 conversion of the chyme into a more viscid mass is to hinder some- 

 what its progress through the intestines ; it clings to the intestinal wall, 

 thus allowing absorption to take place. Bile stimulates peristalsis 

 in the large intestine. 



Bile is alkaline; it therefore assists the pancreatic juice in 

 neutralising the chyme that leaves the stomach. It assists the 

 absorption of fats (see p. 548). It is also a solvent of fatty acids. 



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 



