THE SEAT AND NATURE OF THE OXIDATIONS 513 



by an outside factor which does not enter into the formation of the 

 end-product. This view is strengthened considerably by the fact 

 that living substance contains three types of catalyzing agents in the 

 form of ferments, namely, oxidases, peroxidases and perhydridases. 

 Since these ferments possess a special function in so far as they com- 

 plete the process of respiration, they may be classified as respiratory 

 ferments. As such they are comparable to the class of the "digestive" 

 ferments. Thus, a fat -splitting enzyme (lipase) and protein-splitting 

 enzymes (proteases) have been isolated from many tissues, and fer- 

 ments have also been found which act upon starch (amylase) sugar 

 (diastase) and glycogen (glycogenase). The fact that such catalyzing 

 agents exist in tissues is well illustrated by the phenomenon of auto- 

 lysis or self-digestion. If a tissue is removed from the body under 

 aseptic conditions and is kept warm and moist, it will finally be 

 digested. The same end-products are then formed as may be obtained 

 by boiling this tissue with acids. 



In general, therefore, it may be said that the reductions in living 

 matter occur either in the presence or in the absence of free or bound 

 oxygen. At this time, however, we are chiefly concerned with those 

 of the first type, namely, with the respiratory reductions. In accord- 

 ance with the foregoing discussion it must now be evident that the 

 purpose of respiration is the burning up of the simplest constituents 

 of the body. This combustion is made possible by the respiratory 

 ferments which are produced by the cell and exert their action as 

 soon as the foodstuffs have been sufficiently simplified by the ferments 

 of the digestive type. The former, therefore, are organic catalyzing 

 agents which may be arranged in the following sequence: 



1. Oxidases, produce their action with the help of free oxygen. 



2. Peroxidases, hasten the formation and action of the peroxids, i.e., of those 

 easily oxidizable substances which take up molecular oxygen to form peroxids. 

 These organic peroxids produce the same effects as hydrogen peroxid, from which 

 atomic or active oxygen is removed as follows: H 2 O 2 = H 2 O + O. At the 

 present time, however, no evidence is at hand to prove that hydrogen peroxid 

 is actually formed in the tissues, although it seems that it is produced in the green, 

 leaves of plants in the course of their assimilation of carbon. 



3. Perhydridase, hastens the reduction of the water-molecule by aldehyds. 

 This ferment, therefore, regulates the hydrolytic cleavage and liberates the oxygen 

 of the water. 



4. Catalase, changes hydroperoxid into molecular oxygen and water. This 

 substance is very prone to be formed in the course of these processes either in a 

 direct way or from peroxids. It would eventually destroy life. Consequently, 

 this ferment really serves as a protection to the cell, because it causes its removal. 



The power of the cell to regulate the intensity of its oxidations is 

 dependent upon its faculty of producing ferments of the preceding 

 types. Secondly, it is also evident that the action of the cells is 

 specific, because several of these ferments affect the oxidation of only 

 particular substances. For this reason, special names have been 

 applied to them, such as xanthinoxidase, tyrosinase, etc. The former, 

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