THE BIO-CHEMISTRY OF ANIMALS AND PLANTS 115 



only from the fat of sheep's wool (lanolin), which although 

 isomeric with cholesterin has different properties. It is dextro- 

 rotatory, whilst cholesterin is laevo-rotatory, and has been 

 called Isocholcsterin by Schulze. 



The cholesterins of plants, usually called Phyto-cholesterins 

 or Phytosterins, are less uniform, differing from each other and 

 from cholesterin in melting point, optical activity, and colour 

 reactions. Until recently they were considered to be definite 

 chemical compounds ; but Windaus and Hauth have shown 

 that whilst this is true for sitosterin (from wheat), others, like 

 phytosterin from Malabar beans or rape-seed oil, are mixtures 

 of two substances of different optical activity and melting point. 



With regard to the chemical constitution of cholesterin, all 

 that was known a few years ago was that it had the formula 

 C27H44O (or C 2 7H 4 tiO) and that it represented an unsaturated 

 monatomic alcohol. These conclusions are based on elementary 

 analysis, and on the formation of bromine addition compounds 

 and ethers. These ethers, especially the oleic ether, occur 

 preformed in the organism (in blood serum [Hiirthle] but not 

 in brain [Bunz, Tebb]), and are of special interest as having 

 led O. Lehmann to the discovery of "Fluid Crystals. 1 ' This 

 phenomenon, which has not yet sufficiently attracted the atten- 

 tion of biologists, explains the peculiar " Myelin " forms, which, 

 according to Lehmann, are deformed liquid crystals of oleates 

 of ammonia and other bases. 1 



Our knowledge of the constitution of cholesterin has made 

 great progress during the last few years mainly owing to the 

 researches of Mauthner, Windaus, Abderhalden and Diels and 

 others. It is now certain that cholesterin has nothing in common 

 with fats, carbohydrates, or proteins, but that it belongs to that 

 peculiar class of substances which are called " terpenes." The 

 terpenes have so far only been known to occur in plants, and 

 the proof of the terpene nature of cholesterin establishes a 

 further link between animal and plant biology. 



The Terpenes represent the final products of reduction (in the 

 chemical sense) of plant metabolism and occur chiefly in plant 

 secretions. They possess the general empirical composition of 

 C 10 H 16 (or CioHigO), and are converted by oxidising agents into 

 derivatives of the aromatic hydrocarbon cymene (p-methyl-propyl 



1 See O. Lehmann, Fliissige Krystalle, Leipzig, 1904 ; also R. Schenck, Kry- 

 stallin. Fliissigkeiten, 1905, and O. Vorlander, Krystallflussige Substanzen , 1908. 



