CHAPTER IV. 

 FERMENTS AND FERMENTATION. 



i. Organic Ferments. Since ferments, the activities of 

 which we recognize in so many physiological processes, play a 

 great role in that special chapter of physiology with which 

 these pages deal, namely, alimentation, it may not be amiss 

 to discuss here their general properties. 



Ferments represent only a special class of the so-called 

 catalytic agents, and are in consequence distinguished by the 

 same characteristics as catalyzers in general. A catalyzer is 

 any substance which, without appearing in the end-products of a 

 chemical reaction t alters by its mere presence the rate of this 

 chemical reaction. The catalytic agent is therefore not to be 

 looked upon as the cause of the chemical reaction, for this 

 occurs even in the absence of the catalyzer, only then at a dif- 

 ferent rate. 1 When a catalytic agent increases the velocity of 

 a chemical reaction it is said to be a positive catalyzer; on the 

 other hand, when it decreases the rate of a chemical reaction 

 it is known as &7iegative catalyzer. Examples of positive cata- 

 lyzers will occur to every one. Common ones from inorganic 

 chemistry ap*manganese dioxide, which hastens the de- 

 compositidn of potassium chlorate into potassium chloride 

 and oxygen when heated; and nitrogen tetroxide, which 

 accelerates the oxidation of sulphurous acid into sulphuric in 

 the manufacture of the latter substance. In both instances 



1 OSTWALD: Uber Katalyse, Leipzig. 1902, p. 12. COHE>N: Physical 

 Chemistry for Physicians. Translated by MARTIN H. FISCHER, New 

 Yprk, 1903, p. 35. 



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