598 PRINCIPLES OF GENERAL PHYSIOLOGY 



is a peroxide, and has a higher oxidation potential than the original system. The 

 reaction is what is known as a " coupled reaction." 



There is reason to believe that reactions between three or more different mole- 

 cules at the same time rarely, if ever, take place. Probably all reactions occur in 

 stages between two molecules at a time. 



Those peroxides produced in the autoxidation of phosphorus and in some other 

 cases, have a considerably higher oxidation potential than such peroxides as that of 

 hydrogen. In the presence of water, as in the living cell, peroxides of the former 

 type, if produced, react with water to form hydrogen peroxide. 



Now such a peroxide as that of hydrogen has not sufficient oxidation power to 

 bring about the combustion of glucose, for example. But there are inorganic 

 catalysts, such as iron, and also enzymes, called "peroxidases," which decompose 

 hydrogen peroxide with the liberation of " active " oxygen. These latter enzymes 

 are found in the living cell. 



Since the oxidations brought about by cells do not occur in the absence of 

 oxygen although a peroxidase is present, we must conclude that the peroxide is 

 absent. Hence, the peroxide is formed by the action of molecular oxygen on 

 some autoxidisable substance in the cell. 



In the actual process of autoxidation, another substance, itself difficult of 

 oxidation, may be drawn into the reaction, as it were, and become oxidised. But 

 the peroxides also formed in the process are acted on by the peroxidase of the cell, 

 with formation of additional " active " oxygen. 



Artificial oxidation systems, similar to the natural ones, "oxidases," can be 

 made by the association of colloidal hydroxides of iron or manganese with an 

 emulsoid colloid. The function of the latter appears to be that of maintaining the 

 active constituent in a state of high dispersion and protecting it from aggregation 

 by electrolytes. 



Living tissues also produce reducing systems, which require the presence of 

 substances such as aldehydes in order to show their activity. 



In these reduction processes, the reactions called " hydrolytic-oxidative- 

 reducing " have to be taken into account. The explanation of these reactions. MS 

 given by Bach, will be found in the text. They seem to consist in the decomposition 

 of water and the formation of " unstable complexes " of hydrogen and hydroxyl 

 ions with water molecules. The former acts -as oxygen perhydride, the latter is 

 the hydrate of hydrogen peroxide. 



The perhydride is apparently decomposed by an enzyme, "perhydridase," 

 analogous to peroxidase, with the activation of hydrogen. An enzyme of this 

 nature has been prepared from liver. 



In the living cell, the presence of autoxidisable substances, together with 

 peroxidase, is not in itself sufficient to bring about the oxidations which actually 

 occur. Disintegration of the cell, as by rubbing with sand, nearly puts an end to 

 the consumption of oxygen by it, although the cell constituents are all present as 

 chemical compounds. 



These constituents must be organised into some kind of a mechanism or 

 structure. This is not the ordinary structure visible under the microscope, since 

 the latter may be unaltered, but the power of consuming oxygen absent. 



There are some facts which show that a certain degree of oxygen consumption 

 may remain after disintegration of the morphological structures by rubbing with sand. 



The properties of the cell membrane are of importance for the oxidative 

 processes in the cell. 



The importance of " structure," no doubt, consists partly in the provision of 

 surfaces for adsorption and activation by concentration of the catalysts concerned 

 in the cell processes. Probably the maintenance of ultra -microscopic " reaction- 

 chambers," by provision of senuperrneable membranes, also plays a part. 



