THE CHEMISTRY OF THE ANIMAL BODY. 1001 



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

 combination. This reaction takes place to some extent in the intestine. 



If fatty acid be fed, the chyle in the thoracic duct is found to contain much 

 neutral fat. 1 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 fed, 

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

 in the urine. In its pure form, therefore, it seems to be oxidized with dif- 

 ficulty in the body. 



Glycerin Aldehyde, HOCH 2 .CHOH.CHO, and Dioxyacetone, HOCH 2 .CO.CH 2 



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

 and together are termed glycerose. They have a sweet taste and are the lowest known 

 members of the glycose (sugar) series i. e. substances which are characterized by the 

 presence of either aldehyde-alcohol, CHOH CHO, or ketone-alcohol, CO CH 2 OH, 

 radicals. The constituents of glycerose, from the number of their carbon atoms, are 

 called trioses. On boiling glycerose with barium hydrate the two constituents readily 

 unite to form t-fructose (levulose). 



Glycerin Phosphoric Acid, (HO) 2 C 3 H 5 .H 2 PO 4 . This is the only ethe- 

 real phosphoric acid in the urine. It is found in mere traces, its source being 

 the lecithin decomposed in the body. 2 



Lecithin C H /~ 12 



5 \O.PO.(OH).O.C 2 H 4 .N(CH 3 ) 3 OH. Lecithin is found 



in every cell, animal or vegetable, and especially in the brain and nerves. 

 It is found in egg-yolk, in muscles, in blood -corpuscles, in lymph, pus-cells, 

 in bile, and in milk. On boiling lecithin with acids or alkalies, or through 

 putrefaction in the intestinal canal, it breaks up into its constituents, fatty 

 acids, glycerin phosphoric acid, and cholin (see p. 986), substances which the 

 intestine may absorb. The fatty acids may be stearic, palmitic, or oleic, two 

 molecules of different fatty acids sometimes uniting in one molecule of 

 lecithin : hence there are varieties of lecithins. Through further putrefaction 

 cholin breaks up into carbonic oxide, methane, and ammonia. 3 Lecithin 

 treated with distilled water swells, furnishing the reason for the " myelin 

 forms " of nervous tissue. Lecithin is readily soluble in alcohol and ether. 

 It feels waxy to the touch. Protagon, which has been obtained especially 

 from the brain, is a crystalline body containing lecithin and cerebrin which 

 is a glucoside (a body separable into proteid and a sugar). The chemical 

 identity of protagon is shown in that ether and alcohol will not extract lecithin 

 from it. 4 Protagon readily breaks up into its constituents. While protagon 

 seems to be regarded as the principal form in which lecithin occurs in the 

 brain, simple lecithin is believed to be present in the nerves and other organs. 

 This subject has not been properly worked out. Kegarding the synthesis of 



1 Munk: Virchovfs Arehiv, 1880 ; Bd. 80, p. 17. 



2 Sotnitschewsky : Zeitschrift fur physiologische Chemie, 1880, Bd. 4, p. 214. 



3 Hasebroek : Ibid., 1888, Bd. 12, p. 148. 



4 Gamgee and Blankenhorn : Journal of Physiology, 1881, vol. ii. p. 113. 



