34 PHYSIOLOGY CHAP. 



directly with tincture of guaiacum, peroxidases only in presence 

 of a peroxide. 



Some consider as a third group of the oxidising ferments the 

 so-called catalases, which split up hydrogen peroxide into oxygen 

 and water, but never give a blue reaction with tincture of 

 guaiacum. 



The alcoholic fermentation of glucose by means of beer yeast, 

 or the ferment known as zymase, which was first isolated by 

 Buchner from the cells of that micro-organism, is not a true and 

 proper oxidation in which free oxygen is absorbed by the sugar 

 as may be deduced from the fact that such fermentation takes 

 place anaerobically, and according to the equation : 



C 6 H 12 6 = 2C 2 H 5 OH + 2CO,. 

 Glucose Alcohol Carbonic 

 acid 



It should rather be considered as an internal or intra-molecular 

 oxidation, by which part of the molecule of glucose is oxidised, 

 and burns at the expense of the other part, till it finally splits up 

 into alcohol and carbonic acid. According to recent investigation, 

 we have here the co-operation of two separate and distinct 

 enzymes, one of which, lactolase, or lactacidase, converts sugar into 

 lactic acid, while the other, zymase, or alcoholase, splits the lactic 

 acid into alcohol and carbonic acid. 



According to some authors (whose conclusions have, however, 

 been warmly disputed), a similar anaerobic fermentative process of 

 glycolysis takes place in animal tissues. 



In conclusion we must mention another class of ferments, of 

 which we know at present even less than those already discussed 

 the so-called reducing ferments, reductases or hydrogenases. 



Another classification of enzymes is based upon the difference 

 of place in which they normally occur. Thus, to the ferments 

 known as extracellular or secretory, because normally found in the 

 liquids secreted by the various glands or cells, are opposed the 

 intracellular ferments or endo-enzymes, which are found within 

 the cell, and represent the chemical agents by which the cells are 

 able to split up or fabricate the several chemical components of 

 their substance. To this class of endo-enzymes belong Buchner's 

 zymase, many of the oxidases, and also a series of hydrolytic, 

 proteoclastic enzymes, which according to Vernon are of the type 

 of 0. Cohnheim's erepsin. 



To these intracellular proteolytic ferments are due the 

 phenomena of post-mortem autodigestion or autolysis, described 

 for the first time by Salkowski (1900), which occurs in the organs 

 or organic fluids, when isolated from the body, and kept free of 

 bacterial or extraneous enzymatic contamination. After a certain 

 lapse of time it can be shown that protein cleavage has taken 



