BILIARY CALCULI, or gall-stones.—These concretions have been especially examined by Gren, Thenard, Fourcroy, and as to the fatty matter which they contain, by Chevreul.* Human gall - stones are, for the most part, composed of a crystalline aggregate of a species of adipocere, or as it has been termed by Chevreul, cholesterine, (from zom, bile, and o-rEgEoc, solid,) with more or less colouring matter, muco-albumen, and inspissated bile ; they are accordingly of various colours and textures, but generally brittle and friable. Those which are chiefly cholesterine, or as it should more properly be termed cholestearine, are white and crystalline, and lighter than water • the others are more tough, coloured, and dense ; their specific gravities, therefore, vary from 0.803 to 1.06. Their chemical ex amination may be conducted as follows : they may be powdered, and digested in water to separate the inspissated bile : then boiled in alcohol, and the solution filtered whilst hot ; as it cools it deposits the cholesterine, and often retains common fat and its acids in solu tion. The portion which resists the action of alcohol may be digested in a weak solution of caustic potash, which takes up colouring matter and muco-albumen : the solution, supersatura ted by acetic acid, deposits these, and the co louring matter may afterwards be removed by alcohol. Any common albumen may be de
tected by ferrocyanate of potash added to the acetic solution.
Cholesterine separates in white pearly scales from its hot alcoholic or etherial solution during cooling; it fuses at about 2800, and when heated to about 4000, it sublimes : in the open air it burns like wax. Its ultimate components are 85 carbon, 12 hydrogen, 3 oxygen. It is the most carbonaceous of all the varieties of fat.
The gall-stones of the ox frequently consist chiefly of the yellow colouring matter of the bile, which is occasionally used by painters on account of its brightness and durability : it is in soluble in water and alcohol, but readily solu ble in weak solution of potash, from which it is thrown down in green flocks by muriatic acid : nitric acid cautiously dropped into a solution of this colouring matter gives it various shades of green, blue, and red.