4 CHEMICAL STATICS 



sugar being accelerated to a high degree by one enzyme and by 

 that alone. 

 2. The Products of the Decomposition of the Proteins. — The 



proteins are notoriously liable to decomposition, and a complete 

 breaking down of the sparingly diffusible, difficultly crystallizable 

 proteins, into substances which readily diffuse and crystallize can 

 be brought about by a variety of agencies, such as the following: 



I. Fusion with alkali. 



II. Oxidation with permanganate, chromic acid, etc. 



III. The action of halogens. 



IV. Hydrolysis, through one or more of the following agencies: 



a. Heating in acid solution, 



h. Heating in alkaline solution, 



c. Treatment with superheated steam. 



d. Treatment with enzymes. 



Of all these methods that of hydrolysis is the most satisfactory 

 and yields the most uniform and readily interpretable results. 

 It appears that whatever be the method of hydrolysis employed, 

 the end-result, provided the hydrolysis has been complete, is 

 the same, namely, the production of a mixture of amino-acids. 



Incomplete hydrolysis, however, results in the production of a 

 number of intermediate substances, variously designated, in the 

 order of decreasing complexity, proteoses (albumoses), peptones 

 and polypeptids. The hydrolysis of the proteins, therefore, 

 occurs in stages, just as, in the hydrolysis of starch, intermediary 

 stages (the dextrins and maltose) are passed through, before the 

 attainment of the last stage of hydrolysis and the complete con- 

 version of the starch into glucose. 



It was early recognized that a predominating proportion of the 

 products of the complete hydrolysis of proteins consists of amino- 

 acids, and the most readily detected amino-acids, leucin and tyi'o- 

 sin, were discovered, respectively by Proust in 1818 (54), and^by 

 Liebig in 1846 (44). The chemical constitution of these sub- 

 stances, however, was a discovery of much later date, that of 

 leucin having been established in 1868 by Hlifner (31) and of 

 tyrosin in 1869 by Barth (3). 



The older methods of isolating individual amino-acids from the 

 mixture which the complete hydrolysis of a protein yields, de- 



