456 SUCCUS ENTERIOUS. [BOOK n. 



coloured and amorphous. Less common than the above are small 

 dark coloured stones, having often a mulberry shape, consisting 

 not of bilirubin itself, but of one or other derivative of bilirubin. 

 Gall-stones consisting almost entirely of inorganic salts, calcic 

 carbonates and phosphates, are also occasionally met with. In the 

 lower animals, in oxen for instance, bilirubin gall-stones are not 

 uncommon, but cholesterin gall-stones are rare. 



A gall-stone appears always to contain a more or less obvious 

 ' nucleus/ around which the material of the stone has been de- 

 posited, and which may be regarded as the origin of the stone ; 

 the real cause of the formation of the stone lies however in certain 

 changes in the bile, by which the cholesterin, or bilirubin, or other 

 constituent ceases to remain dissolved in the bile. But we cannot 

 discuss this matter here. 



