THE BILE. 177 



rich in cholesterin, while the pigment-stones which are so common 

 in cattle are less frequently seen in the human being. 



The common cholesterin which is found in the animal body has 

 the composition C^H^O or C^H^O, and apparently contains an 

 alcoholic hydroxyl group. There is evidence to show that it be- 

 longs to the class of terpenes, which occur widely distributed in the 

 vegetable world, and which had previously not been recognized as 

 existing in the animal world. This shows at the same time that 

 the animal organism contains hydro-aromatic compound. It com- 

 bines with fatty acids to form compound esters which are analogous 

 to the fats, and in this form also cholesterin occurs widely distrib- 

 uted in the animal world. The common lanolin of wool-fat thus 

 contains large amounts of esters, both of cholesterin and its isomeric 

 compound isocholesterin. On treating cholesterin with concentrated 

 sulphuric acid the substance gives rise to the formation of hydro- 

 carbons, which are termed cholesterilins, which stand in a close re- 

 lation to the terpene group. With iodine these bodies give a blue 

 color. 



Cholesterin usually occurs in the form of colorless, transparent 

 plates, with ragged margins and angles, which are very characteristic. 

 It is practically insoluble in water, dilute acids and alkalies, but dis- 

 solves with ease in ether, chloroform, benzol, and in boiling alcohol. 

 From its ethereal solutions it crystallizes out in the form of fine 

 needles. It is further soluble in the essential and fatty oils, as also 

 in the presence of biliary acids. Its crystals melt at 145 C. 



Tests. SALKOWSKI'S TEST. A few crystals of cholesterin are 

 dissolved in a small amount of chloroform and treated with an 

 equal volume of concentrated sulphuric acid. The solution of 

 cholesterin then first assumes a blood-red color, and then gradually 

 turns to a violet red, while the sulphuric acid appears dark red and 

 shows a green fluorescence. On pouring the chloroform into a 

 shallow porcelain dish it turns violet, then green, and finally becomes 

 yellow. 



THE TEST OF LIEBERMANN-BURCKHARD. If a small amount 

 of cholesterin is dissolved in about 2 c.c. of chloroform and is 

 treated with 10 drops of acetic acid anhydride, and subsequently 

 with concentrated sulphuric acid, the solution at first assumes a red, 

 then a blue, and finally a green color. The latter develops at 

 once if cholesterin is present only in traces. 



Isolation. To prepare cholesterin for purposes of study, it is 

 most convenient to isolate the substance from cholesterin stones. 

 To this end, the concretions are finely pulverized and extracted 

 with boiling water and then with boiling alcohol. From the 

 alcoholic extract the cholesterin crystallizes out on cooling, and is 

 then boiled with an alcoholic solution of sodium hydroxid, so as to 

 saponify the fats which are at the same time present. The alcohol 

 is then distilled off and the residue extracted with ether, which 

 removes the cholesterin and leaves the soaps behind. On evaporat- 

 ing this extract, after filtration, the substance is obtained in crystal- 

 is 



