THE NONNITROGENOUS SUBSTANCES 79 



other substances. In protagon which occurs in the white substance of the cen- 

 tral nervous system, and probably represents a mixture of substances, lecithin 

 is bound up with the cerebrosides, N-coiitaining, phosphorus-free substances, 

 which on boiling with dilute mineral acids yield a reducing sugar. Ovo- 

 vitillin is a combination of proteid and lecithin, and similar compounds are said 

 to be obtained as insoluble residues from peptic digestion of the gastric mu- 

 cosa, liver, kidneys, etc. These lecithin albumins represent therefore a new 

 group of proteids (cf. under B). Jecorin, which has been demonstrated in the 

 liver and in the blood, is a combination of lecithin and glucose. 



2. THE NONNITROGENOUS SUBSTANCES 

 A. FATS 



The fats are esters of the triatomic alcohols, the glycerins, with mono- 

 basic fatty acids, chief of which in the animal fats are : stearic acid, C 18 H 36 2 , 

 palmitic acid, C 16 H 32 2 , and oleic acid, C 18 H 34 2 . The triglycerides of the 

 first two stearin, C 3 H 5 .(C 18 H 35 2 ) 3 , and palmitin, C 3 H 5 .(C 16 H 31 2 ) 3 melt 

 only at a temperature far above that of the body. The glyceride of oleic acid, 

 olein, C 3 H 5 .(C 18 H 33 2 ) 3 , is on the other hand fluid at ordinary temperatures 

 and solidifies in the form of crystalline needles only at 5 C. The melting 

 point of a mixture of the three glycerides must therefore depend upon the rela- 

 tive content of olein the greater the relative quantity of this, fat, the lower is 

 the melting point of the mixture. Moreover the melting point of fat shows 

 considerable variation not only in different species of animals, but also in 

 different parts of the same individual, which means that the relative quantity 

 of olein present varies considerably. Traces of fatty acids are also found in 

 animal fat. 



The following reactions, among others, serve to distinguish the different 

 fats : (1) the acid equivalent, which is the measure of the content of free acid in a 

 fat, and is obtained by titration of the fat dissolved in alcohol ether with n/10 

 alcoholic caustic potash; (2) The saponification equivalent i.e., the number of 

 mg. of KOH combined with fatty acid in saponification of 1 g. of the fat with 

 alcoholic caustic potash; (3) The Reichert-Meissl equivalent, which gives the 

 amount of volatile fatty acid obtained, when, after saponification, the fat is 

 distilled off in the presence of a mineral acid ; (4) The iodine equivalent i. e., 

 the quantity of iodine taken up by a fat, and serving as the measure of the 

 content of olein. 



In the body fat is to be found for the most part inclosed in the cells of 

 the fatty tissues. These represent in fact a kind of storehouse for fats (cf. 

 Chapter IV). It occurs also in very small quantities in the blood and in 

 other fluids of the body. 



Fats are insoluble in water, are dissolved by boiling-hot alcohol, but are 

 precipitated again on cooling. They are readily soluble in ether, benzol and 

 chloroform. On boiling with caustic alkalies they are decomposed and are 

 split into glycerin and fatty acids, the latter of which unite with the alkali 

 to form soap. The fatty acids are set free from the soap by strong acids. 

 Like the neutral fats they are soluble in ether, but this is not the case with 

 soaps. 



