2 PHYSIOLOGICAL CHEMISTRY. 



occurred without aid from the original cell It was not until 1897, 

 however, that this theory was placed upon a firm experimental 

 basis. This was brought about through the efforts of Buchner 

 who succeeded in isolating from the living yeast cells a substance 

 (zymase) which, when freed from the last trace of organized cel- 

 lular material, was able to bring about the identical fermentative 

 processes, which, up to this time, had been deemed possible only 

 in the presence of the active, living yeast cell. 



Buchner's manipulation of the yeast cells consisted in first grind- 

 ing them with sand and infusorial earth after which the finely 

 divided material was subjected to great pressure (300 atmospheres) 

 and yielded a liquid which possessed the fermentative activity of 

 the unchanged yeast cell. 1 This liquid contained zymase , the prin- 

 cipal enzyme of the yeast cell. Later the lactic-acid- and acetic- 

 acid-producing bacteria were subjected by Buchner to treatment 

 similar to that accorded the yeast cells, and the active intracellular 

 enzymes were obtained. Many other instances are on record in 

 which a soluble, active, agent has been isolated from ferment 

 cells, with the result that it is pretty well established that all the 

 so-called organized ferments elaborate substances of this character. 

 Therefore, basing our definition on the work of Buchner and 

 others we may define an enzyme, as an unorganized, soluble ferment, 

 which is elaborated by an animal or vegetable cell and whose ac- 

 tivity is entirely independent of any of the life processes of such- 

 a cell. According to this definition the enzyme zymase elaborated 

 by the yeast cell is entirely comparable to the enzyme pepsin elabor- 

 ated by the cells of the stomach mucosa. One is derived from a 

 vegetable cell, the other from an animal cell, yet the activity of 

 neither is dependent upon the integrity of the cell. 



Enzymes act by catalysis and hence may be termed catalyzers 

 or catalysts. A simple rough definition of a catalyzer is " a sub- 

 stance which alters the velocity of a chemical reaction without un- 

 dergoing any apparent physical or chemical change itself and with- 

 out becoming a part of the product formed." It is a well-known fact 

 that the velocity of the greater number of chemical reactions may 

 be changed through the presence of some catalyzer. For example, 

 take the case of hydrogen peroxide. It spontaneously decomposes 

 slowly into water and oxygen. In the presence of colloidal plati- 



1 In later investigations the process was improved by freezing the ground cells 

 with liquid air and finely pulverizing them, before applying the pressure. 



