CHOLESTEROLS 3*9 



THE CHOLESTEROLS. 



Cholesterol. 



Cholesterol was discovered in bile and has been found in the bile 

 of all animals with one exception. It has since been shown to be 

 present in small quantities in blood and the tissues of man and 

 animals ; in somewhat large quantities it is present in bone marrow 

 and nervous tissue. It is very seldom found in urine and, when 

 found, only in the smallest quantities. Crystalline deposits of choles- 

 terol are found in pathological effusions, in pus and in diseased arteries. 

 Gallstones usually consist almost entirely of cholesterol. Not only is 

 cholesterol present as such, but also in the form of its esters with 

 the higher fatty acids. Lanolin, or wool fat, is composed mainly of 

 esters of cholesterol 



Constitution. 



Cholesterol has been shown to contain an OH group and to be 

 a secondary alcohol by oxidation to a ketone. It contains one un- 

 saturated bond and an isoamyl group. It belongs to the group of 

 terpenes and its formula according to Windaus is the following : 



CH 3 \ 



\CH . CH 2 . CH 2 C U H 17 



CH CH 



/\ /\ 



H 2 C CH CH . CH 3 



H 2 C CH,, CH 



\/ H 



CHOH CH 2 . 



The structure of C n H 17 has still to be determined. 

 Preparation. 



(1) From Gallstones. 



Cholesterol is most easily prepared from gallstones. The powdered 

 stone is extracted with a mixture of ether and alcohol. The filtered 

 solution on evaporation leaves a residue of cholesterol. It is purified 

 by boiling with alcoholic potash, the solution is evaporated to dryness 

 and the residue extracted with ether. The crystals obtained after 

 evaporation of the ether are recrystallised from alcohol. 



(2) From Brain. 



Sheep's brain is thoroughly ground up with some sand and about 

 3 parts of plaster of Paris. This mass when it has become hard is 

 powdered and covered with acetone. Dried sheep's brain is extracted 

 with acetone. The acetone is filtered off and the mass again treated 

 with acetone. On distilling off the acetone, crystals of cholesterol 

 remain. They may be purified as above. 



