CHAPTER II. 

 THE PROTEIN SUBSTANCES. 



THE chief mass of the organic constituents of animal tissues consists 

 of amorphous nitrogenized, very complex bodies of high molecular weight. 

 These bodies, which are either proteins in a special sense or bodies nearly 

 related thereto, take first rank among the organic constituents of the 

 animal body on account of their great abundance. For this reason they 

 are classed together in a special group which has received the name 

 protein group (from Trpcorcvw, I am the first, or take the first . (place) . 

 The bodies belonging to these several groups are called protein sub- 

 stances, although in a few cases the protein bodies in a special sense are 

 designated by the same name. 



The several protein substances 1 contain carbon, hydrogen, nitrogen, and 

 oxygen. The majority contain also sulphur, a few phosphorus, and a 

 few also iron. Copper, chlorine, iodine, and bromine have been found 

 in some few cases. On heating the protein substances they gradually 

 decompose, producing a strong odor of burned horn or wool. At the same 

 time they produce inflammable gases, water, carbon dioxide, ammonia, 

 and nitrogenized bases, besides many other substances, and leave a large 

 quantity of carbon. On deep hydrolytic cleavage they yield abundance 

 of a-monamino-acids of various kinds as decomposition products. 



The nitrogen occurs in the protein bodies in various forms, and this 

 is also revealed in the division of the nitrogen among the cleavage prod- 

 ucts. On boiling with dilute mineral acids we obtain (1) so-called amide 

 nitrogen, which is readily split off as ammonia; (2) a guanidine residue 

 which is combined with diaminovaleric acid as arginine, and which 

 has also been called the urea-forming group; (3) basic nitrogen or diamino- 

 acid nitrogen, or hexone bases nitrogen, which is precipitated by phos- 

 photungstic acid as basic products (to which also the guanidine residue 

 of arginine belongs); (4) monamino-acid nitrogen; and (5) the nitrogen 



1 See " Eiweisskorper," Ladenburg's Handworterbuch der Chemie, 3, 534-589, 

 which gives a complete summary of the literature of protein substances up to 1885. 

 The more recent literature may be found in O. Cohnheim, Chemie der Eiweisskorper, 

 Braunschweig, 1911. See also Oppenheimer's Handbuch der Biochem. der Menschen 

 und der Tiere, 1908. 



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