CHAPTER III. 

 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 Trpoxrcvo, 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 burnt horn or wool. At the same time they 

 produce inflammable gases, water, carbon dioxide, ammonia, and nitro- 

 genized bases, besides many other substances, and leave a large quantity 

 of carbon. On hydrolytic cleavage they all yield, besides nitrogenous 

 basic substances, especially large amounts of a-monamino-acids of 

 different kinds. 



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 diaminovalerianic acid as arginine, and 

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

 or diamino-acid nitrogen, which is precipitated by phosphotungstic 

 acid as basic products (to which also the guanidine residue of arginine 



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 up to the year 1903 may be found in O. Cohnheim, 

 Chemie der Eiweisskorper, Braunschweig, 1904. See aslo Mann, Chemistry of the 

 Proteids, London, 1906, and Oppenheimer's Handbuch der Biochem. der Menschen 

 und der Tiere, 1908. 



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