LIVER. 165 



The gall bladder is a reservoir in which the bile is stored till 

 required in the intestine; but although very generally found 

 in all classes of vertebrata, there are some animals in which 

 it is absent. 



123. The Bile contains a large amount of mucus derived 

 from the glands of the ducts, no doubt of some important 

 use; but what that use is, unless it be to protect the mucous 

 membrane of the ducts and gall bladder from the action of 

 bile long left in their interior, is unknown. It contains also 

 a special colouring matter, rich in iron, and no doubt derived 

 from the colouring matter of the blood, so much of which is 

 found in the serum of the splenic vein. But the most 

 characteristic substances are those which give it the proper- 

 ties of a soap, as stated in a previous page (p. 102). These 

 substances are termed the glycocholate and taurocholate of 

 soda. Their acids are of very complex composition, and 

 easily resolved, the one into cholic acid and glycin, the other 

 into cholic acid and taurin. Cholic acid is a substance very 

 similar in composition to the ordinary fatty acids, having, 

 like them, a large number of equivalents of carbon and 

 hydrogen in combination with a much smaller quantity of 

 oxygen; glycin and taurin are bases of comparatively simple 

 chemical formula, and containing nitrogen, while taurin 

 contains sulphur in addition. It will be noted, therefore, 

 that the biliary acids must be formed, at least in part, from 

 the nitrogenous constituents of the blood. They do not pre- 

 exist in the blood, but are manufactured by the liver; for 

 they are never found even in the smallest quantity in analyses 

 of healthy blood. Bile likewise contains phosphates in 

 quantity; also a certain amount of cholesterin, a non-nitro- 

 genous crystalline substance, allied to the fats, and crystal- 

 lizing in large quadrilateral plates, a constituent of the 

 brain, and very possibly brought to the liver from that 

 source. 



From experiments on animals, in which the bile is gathered 

 by means of a fistulous opening, the flow would appear to 

 be very great, and is calculated at two or three pounds per 

 diem in the human subject. It is increased a few hours 

 after eating, and reaches its maximum about the eighth hour, 

 then gradually diminishes while fasting is continued. The 



