90 INTRODUCTION TO GENERAL PHYSIOLOGY 



to it in its ordinary form. Although this can be done in various 

 ways, we do not as yet understand completely what is the change 

 that takes place. Sir W. Ramsay taught that its activity was 

 manifested during the change from the quadrivalent to the 

 bivalent form, that is, in the process of losing electrical charge. It 

 is interesting to connect this view with what was pointed out 

 previously in our general discussion of the energetics of living 

 organisms, namely, that it is in the process of transfer of energy 

 that those activities which we recognise especially as manifestations 

 of life are to be found. 



The way in which the " activation " of oxygen takes place in the 

 living cell may be described briefly, as follows. 



Although most of the materials oxidised in the cell are 

 refractory to ordinary oxygen, certain constituents are slowly 

 oxidised by it. Such are the unsaturated fats and lipines. These 

 are said to undergo a process of " autoxidation " (E., p. 202). Now, 

 in this process, investigation has shown that a rather curious thing 

 happens. When a part of the substance is oxidised to a simple 

 oxide, energy is given off, as in the ordinary process of combustion. 

 But this energy is not entirely lost as heat in the case of autoxida- 

 tion. Simultaneously with the oxidation of one molecule to a 

 lower oxide, another one is converted to a peroxide, which requires a 

 supply of energy to put in the extra atom of oxygen. Peroxides 

 have higher powers of oxidation than ordinary oxygen has ; they 

 supply oxygen to oxidisable substances at a higher potential 

 than it possesses in its ordinary molecular form. 



A rough idea of this process of raising chemical potential 

 may be obtained by thinking of the increased destructive effect 

 of a weight when dropped from a greater height. To this 

 greater height it must have been raised by the doing of work 

 upon it. 



But even peroxides are not powerful enough to oxidise sugar 

 or lactic acid. Hydrogen peroxide does not cause the evolution 

 of carbon dioxide from lactic acid (E., p. 203). There is, however, 

 a catalytic means by which hydrogen peroxide and similar 

 peroxides can be made to afford oxygen at a higher potential. 

 The addition of a trace of a ferrous salt (Fenton's reaction) results 

 in the complete oxidation of lactic acid to carbon dioxide and 

 water (E., p. 203). What the exact mechanism of this reaction is, 

 has not been completely explained. 



We may ask, has there been found in the living cell any agent 

 similar in action to that of the iron salt in the above reaction ? In 

 the following description, when certain enzymes are stated to be 

 obtained from particular sources, it is not to be understood 

 that they are only present there, but that from this source they 



