CHAPTER II. 



THE PROTEIN SUBSTANCES. 



THE chief mass of the organic constituents of animal tissues 

 consists of amorphous, nitrogenized, complex bodies of high molecu- 

 lar weight. These bodies, which are either albuminous 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 TtpGorevco, 

 I am the first or take the first place). The bodies belonging to 

 these several groups are called protein substances, although in a 

 few cases the albuminous bodies in a special sense are designated 

 by the same name. 



The several protein substances contain carbon, hydrogen, nitro- 

 gen, and oxygen. They generally contain also sulphur, a few 

 phosphorus, and a few also iron. Copper has been found in some 

 few cases. On heating the protein substances they gradually de- 

 compose, producing inflammable gases, ammoniacal compounds, 

 carbon dioxide, water, nitrogenized bases, as well as many other 

 bodies, and at the same time they emit a strong odor of burnt horn 

 or wool. More highly heated they leave a porous, shining mass of 

 carbon, and when this is thoroughly burnt an ash is obtained con- 

 sisting chiefly of calcium and magnesium phosphates. The ques- 

 tion whether the mineral bodies left by burning exist as impurities 

 or whether they are constituents of the protein molecule has not 

 been decided. 



It is at present impossible to decide on a classification of the 

 protein substances based upon their properties, reactions, and con- 

 stitution, as well as upon their solubilities and precipitations, corre- 

 sponding to the demands of science. The best classification is 

 perhaps the following systematic summary of the better known 



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