188 W. K. BLOCK 



of the benzene scries should perhaps he included since they arc found in 

 certain natural oils (chalmougTa oil, etc.). The fatty acids most fre- 

 quently found in animals are palmitic, oleic and stearic acids. In active 

 tissues fatty acids of the linoleic and possibly of still more unsaturated 

 series are to he found, while in the brain hydroxy acids are present, to- 

 gether with a great variety of unsaturated fatty acids. 



In milk are to be found all known even numbered members of the 

 .acetic acid series, beginning with butyric and ending with arachidic. 



titerols. -This group includes the alcohols found naturally in com- 

 bination with the fatty acids in the waxes. They are generally inert 

 substances of large molecule, mainly of the straight chain monatomic group 

 of alcohols. The notable exceptions to this rule are cholesterol and related 

 substances, secondary alcohols belonging to the terpene series; most 

 sterols occur in the free as well as in the combined form. The more im- 

 portant members of this group are cetyl (C 10 H : , 4 O) and octodecyl 

 (C 18 H as .O) alcohols in spermaceti, ceryl alcohol (C^H^O) in Chinese 

 wax, myricyl alcohol (C :lo II oO) in beeswax, cocceryl (C :{0 IT (!2 O 2 ) in 

 cochineal wax and the cholesterol group containing cholesterol (C 27 H 44 0) 

 in most animal tissues and fluids, the isomeric phytosterol similarly dis- 

 tributed in plants, isoeholesterol (C 2r .II 4G O) and a number of others more 

 or less well characterized. Cf these, the only one which calls for extended 

 discussion is cholesterol. According to our present information it is a 

 monatomic secondary alcohol with a terminal vinyl group. The nucleus 

 probably contains four to six carbon rings and belongs in the general 

 group of terpenes. The details of structure are illustrated in the formula: 



CH 3 



\ 



CH . CHo . CHo . C, 7 Ho,,CH : CH 2 



/ / \ 



CH 3 HoC Clio 



\ / 



CH(OH) 



In the free form or as esters with the fatty acids it is widely distributed 

 in animal tissues and fluids and either as such or as various derivatives 

 (the bile acids have been so regarded) it is probably of great importance 

 in animal metabolism. 



Cf the fatty acids those most frequently found in combination with 

 cholesterol are oleic and palmitic acids. 



Cholesterol is a colorless, odorless substance crystallizing in thin 

 plates, insoluble in water, soluble in fats and fat solvents, melting at 

 148.5 C., and is optically active. Specific rotation [a] y = 20.92. 

 The corresponding alcohol in plants is phytosterol which, Recording to 

 Gardner, changes to cholesterol during intestinal absorption in animals. 



