CHOLESTERIN. 277 



colourless, transparent, very lustrous, lighter than water, and 

 melts at 68 into a colourless fluid, which very slowly reassumes 

 the solid form ; it can be distilled for the most part undecom- 

 posed, and burns with a smoky flame. It is insoluble in water, 

 but dissolves freely in alcohol and ether, and in the volatile and 

 fatty oils. 



b. Cholesterone is extracted by ether from the residue insoluble 

 in alcohol ; it occurs in fine white needles, melts at 175, cannot be 

 distilled without partial decomposition, is lighter than water, is 

 devoid of taste and smell, and burns with a smoky flame. Both 

 varieties of cholesterone are devoid of oxygen, but contain about 

 12 parts hydrogen to 88 of carbon. 



Preparation. The best method of preparing cholesterin is by 

 boiling gall-stones, containing this substance, with alcohol, and 

 filtering the solution while hot; by recry stall isation from hot alco- 

 hol it is easily obtained in a state of purity. 



Tests. The recognition of cholesterin in the animal fluids is 

 by no means so easy as might be supposed from the distinctive 

 characters of this body ; if, however, it has been once separated in 

 a crystalline form, nothing is easier than to diagnose its presence 

 with certainty. If, by its insolubility in water, acids, and 

 alkalies, and by its solubility in alcohol and ether, it has been 

 recognised as a fatty substance, it may be readily distinguished 

 from all other similar substances by a measurement of the angles 

 of the rhomb. It is only necessary to remark that the tablets 

 are often so thin that their contour may be easily overlooked in a 

 microscopic examination, if other morphological substances are 

 simultaneously present in the field of the microscope : we must 

 then slightly shade the field by a lateral or central diaphragm to 

 make the outline stand forth more distinctly. In all this there is 

 no difficulty ; but it is, on the other hand, often very troublesome 

 to obtain this substance in a crystalline form from oily fluids 

 containing bile, or from soapy solutions. If we saponify with an 

 alkali the fat which holds the cholesterin in solution, it also 

 dissolves in the soap-water, and on the addition of an acid is 

 again converted into the fatty acid; hence, when dealing with 

 very small quantities of cholesterin, it is necessary to combine 

 the fatty acid with oxide of lead, and to extract with boiling 

 alcohol; the small quantity of dissolved margarate of lead is 

 usually deposited previously to the separation of the cholesterin, 

 which frequently does not crystallise, so as to be recognised by 

 the microscope, until the fluid has been submitted to evaporation. 



