558 AJV AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



Monamide of Amido-succinic Acid, or Asparagin, IT,NOC.C,H 3 NH. 2 .COOH 

 — This is found widely distributed in plants, especially in the germinating seed. If a plant 

 be placed in the dark its proteid nitrogen decreases, whereas the non-proteid nitrogen 

 increases, 1 the cause of this being attributed to proteid metabolism with the production of 



amido- acids, i. < . aspartic and glutamic acids, leucin, and tyrosin. In the sunlight, it 

 is believed, these bodies arc later reconverted into proteid. One view regarding the for- 

 mation of asparagin is based theoretically on the production of succinic acid from carbo- 

 hydrates (as in alcoholic fermentation) and the subsequent formation of oxysucrinic acid 

 (or malic acid, HOOC.C,H 3 OH.COOH), which the inorganic nitrogenous salts change 

 to asparagin. 2 At any rate asparagin in the plant has the power of being constructed into 

 proteid. Since proteid in the animal body may yield 60 per cent, of dextrose in its 

 decomposition, as will be shown, it seems fair to surmise that the synthesis of proteid in 

 the plant may in part depend upon the union of asparagin or similar amido- compounds 

 wit li the carbohydrates present. Asparagin if fed is converted into urea. It forms no 

 proteid synthesis in tin' animal, and lias only a very small effect as a food-stuff. 3 



Glutamic acid, H00C.( , I1NI1,.( , II,.*CH 2 .C001I.— This is found as a cleavage- 

 product of tryptic digestion in the intestinal canal. Glutamin, its amido- compound, is, like 

 asparagin, widely distributed in the vegetable kingdom and in considerable amounts. It 

 probably plays the same role as asparagin in the plant. Glutamin is more soluble than 

 asparagin and is therefore less easily detected. 



Compounds of Triatomic Alcohol Radicals. 



Glycerin, or Propenyl Alcohol, CH 2 OH.CHOH.CH 2 OH. The glycerin 

 esters of the fatty acids form the basis of all animal and vegetable fats. 

 Glycerin is furthermore formed in small quantities in alcoholic fermentation. 



Preparation. — (1) Through the action of an alkali on a fat, glycerin and a 

 soap are formed, a process called saponification: 



2C 3 H 5 (C 18 H 35 2 ) 3 + 6XaOH = 2C 3 H 5 (OH) 3 + GNaC^O,. 



Stearin. Sodium stearate. 



(2) Fats may be decomposed into glycerin and fatty acid by superheated 

 Steam, and likewise by the fat-splitting ferment in the pancreatic juice. Thus, 

 if a thoroughly washed butter-ball, consisting of pure neutral fat, be colored 

 with blue litmus, and a drop of pancreatic juice be placed upon it, the mass 

 will gradually grow red in virtue of the fatty acid liberated from its glycerin 

 combination. This reaction takes place in the intestine. 



If fatty acid la- led, the chyle in the thoracic duet is found to contain much 

 neutral fat.' This synthesis indicates the presence of glycerin in the body — 

 perhaps, in this case, in the villus of the intestine: the source of this glycerin, 

 whether from proteid or carbohydrates, is problematical. If glycerin be 1'ed, 

 only little is absorbed (since diarrhoea ensues), and of thai little some appears 

 in the urine. It seems, therefore, to be oxidized with difficulty in the body. 



Glycerin Aldehyde, IIOCH 2 .CHOH.CHO, and Dioxyacetone, HOCH. 2 .CQ.CH 2 

 Oil. — These substances are formed by the careful oxidation of glycerin with nitric acid, 

 and together are termed glycerose. They ha\e a sweet taste and are the lowest known 



1 Schulze and Kisser: Landwirthschatfliche Versucks-Staiion, 1889, Bd. 36, S. 1. 



' Miiller: Ibid., 1886, Bd. 33, S. 326. 



3 See Voit : Zeitschrift fur Biologic, 1892, Bd. 29, B. 126. 



* Munk: Virchovfs Archiv, 1880, Bd. 80, S. 17. 



