122 PHYSIOLOGICAL CHEMISTRY. 



A. Hydrolytic Reactions. 



B. Oxidation Reactions. 



C. Bacterial Decompositions. 



A brief discussion of the important changes coming under 

 each one of these heads will now follow. 



A. HYDROLYTIC REACTIONS. 



The most important of our ferment reactions, with one 

 exception perhaps, and at the same time the most thoroughly 

 studied, the changes involving hydrolysis have long claimed 

 the attention of chemists. The true nature of some of these 

 reactions is easily recognized and the earlier workers in this 

 field were able to compare the behavior of the enzymes in 

 question with that of dilute hydrochloric or sulphuric acid. 

 In other very important cases this analogy is far less readily 

 pointed out and it remained for recent workers to satisfac- 

 torily establish the true relations. When malt digests starch 

 or when certain enzymes convert the malt sugar formed into 

 glucose the general nature of the changes, as requiring the 

 addition of water, may be shown without difficulty. But with 

 the behavior of pepsin in digesting protein we have more dif- 

 ficulty. Here the reaction is not so easily followed, and the 

 quantitative relations between the original substances and the 

 products formed are more complicated than is the case with 

 the carbohydrate decompositions. However, these reactions 

 likewise have been shown to involve true cases of water addi- 

 tion and therefore may be properly grouped with the carbo- 

 hydrate reactions as hydrolytic. 



This hydrolytic ferment activity is exhibited mainly in the 

 following directions : 



1. In the rrjxiification of carbohydrates as illustrated by 

 the saccharification of starch and further changes in the sugar 

 thus formed, and in other sugars. 



2. In the breaking down of glucosides. 



3. In the splitting of fats. 



4. In the digestion of proteins. 



