PLANT CONSTITUENTS — FATS, PROTEINS 281 



nerve tissue. Its occurrence here is thought to be connected 

 with the other substance which we have referred to, viz. 

 lecithin. It is also thought to be connected with the action 

 of certain toxins. It is found in the bile, where it causes the 

 formation of a certain kind of gall stone. The constitutional 

 formula for these two compounds has not been fully established, 

 but they are probably secondary alcohols containing both an 

 unsaturated group and a hexahydrohenzene ring, and related to the 

 terpenes. Therefore, without going into details, we may simply 

 say that monatomic alcohols of high carbon content known 

 as phytosterol and stigmasterol in plants and cholesterol in 

 animals are found associated with vegetable and animal fats. 



These alcohols are non-saponifiable, so that when fats con- 

 taining them are saponified they remain as unsaponifiaUe 

 matter. In analytical determinations of fats the unsaponifiable 

 matter, as usually determined, consists largely of these com- 

 pounds. They are soluble in ether and in alcohol and may be 

 removed from a saponified fat by extraction with ether. 



Phytosterol and cholesterol are very similar in all their 

 properties and have melting points very close together. They 

 cannot, therefore, be separated or identified by determining 

 their melting points. They each yield an ester with acetic 

 acid, however, and these esters have distinctly different melt- 

 ing points which thus makes it possible to identify them. 



Cholesterol acetate m. p. 114.3°-! 14.8° 



Phytosterol acetate m. p. i25°-i37° 



It is possible that this difference in melting point is due to the 

 fact that phytosterol is not an individual compound but a 

 mixture of several similar ones such as stigmasterol. 



The importance of these two compounds is mainly in the 

 fact that the presence of phytosterol in a fat establishes the 

 fat as of vegetable origin, while cholesterol is present only in 

 animal fats. As to their food value nothing is known. It is 

 probable that the cholesterol in animals is derived from the 

 phytosterol in the plants which the animal uses as food. If 



