22 NUTRITION OF FARM ANIMALS 



Chemically, waxes are defined as fatty acid esters of alcohols other 

 than glycerol, while the fats have already been denned as the fatty 

 esters of glycerol. This distinction is far from according with com- 

 mon usage. Under it many substances popularly known as waxes 

 are technically fats, as for example, Japan wax and in part beeswax. 

 On the other hand, numerous materials ordinarily regarded as oils or 

 fats must be designated as waxes. One of the most familiar bodies 

 of this class is spermaceti, commonly regarded as a fat, which consists 

 chiefly of the palmitic ester of cetyl alcohol, CH 3 (CH 2 )i4CH 2 OH, and 

 sperm oil, which contains no glycerids, would also be regarded as a 

 liquid wax. Similarly wool fat is chemically a mixture of waxes, in- 

 cluding the stearic esters of cholesterin and isocholesterin. Beeswax 

 is likewise in part a true wax, containing the palmitic ester of myricyl 

 alcohol, CH 3 (CH2)28CH 2 OH. The secretion of the anal glands of 

 certain birds contains esters of octodeckyl alcohol, CisHsyOH. 



Cholesterins 



36. Substances of this group are found in the nonsaponifiable resi- 

 due of various fats. In the animal organism they are found widely 

 distributed through the tissues in small amounts and are appar- 

 ently normal constituents of protoplasm. As just noted, they are 

 especially abundant in wool fats in combination with stearic acid. 

 They are also widely distributed in plants. Their exact constitution 

 is still unknown, but they contain a single alcohol hydroxyl and ap- 

 parently belong to the terpene group. Their formula is C 2 7H440H, 

 or C 2 ?H460H, more probably the latter. From the chemical point 

 of view, they are entirely unrelated to the other groups classified as 

 lipoids, but biologically their functions appear to be closely related 

 to those of the other ether-soluble cell constituents. 



. Phosphatids or Phospholipins 



37. Lecithins. Quite closely related to the fats are the 

 substances known as lecithins, which are sometimes, although 

 inexactly, called phosphorized fats. Like the fats, the leci- 

 thins are esters of glycerol. They differ from the fats in that 

 only two of the hydroxyls of the glycerol are replaced by fatty 

 acid radicles, the third being replaced by phosphoric acid 

 which is also in combination with the nitrogenous base cholin, 

 a derivative of glycol. The lecithins, therefore, contain, in 

 addition to carbon, hydrogen and oxygen, both phosphorus and 

 nitrogen. 



