512 THE LIVER [CH. XXXIII. 



It gives the following colour tests : 



1. Heated with sulphuric acid and water (5:1), the edges of the 

 crystals turn red. 



2. A solution of cholesterin in chloroform, shaken with an equal 

 amount of concentrated sulphuric acid, turns red, and ultimately 

 purple, the subjacent acid acquiring a green fluorescence. (Salkowski's 

 reaction.) 



"The mode of origin of cholesterin in the body has not been 

 clearly made out. Whether it is formed in the tissues generally, in 

 the blood, or in the liver, is not known ; nor has it been determined 

 conclusively that it is derived from albuminous or nervous matter. 

 It is also doubtful if we are to regard it as a waste substance of 

 no use to the body, as its presence in the blood -corpuscles, in 

 nervous matter, in the egg, and in vegetable grains, points to a 

 possible function of a histogenetic or tissue-forming character." 

 (McKendrick.) 



A substance called iso-cholesterin, isomeric with ordinary chole- 

 sterin, is found in the fatty secretion of the skin (sebum); it is 

 largely contained in the preparation called lanoline made from sheep's- 

 wool fat. It does not give Salkowski's reaction with chloroform and 

 sulphuric acid just described. 



The Uses of Bile. Bile is doubtless, to a large extent, excretory. 

 Some state that it has a slight action on fats and carbohydrates, 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 proteid. 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 is alkaline ; it therefore assists the pancreatic juice in neutral- 

 ising the acid mixture that leaves the stomach. 



Bile assists the absorption of fats, as we shall see in studying that 

 subject. 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 



