342 



PROTOPLASM 



It is often stated that such and such a process is oxidation, and 

 another reduction; thus, respiration is said to be oxidation, and 

 assimilation reduction, but actually the oxidation of one sub- 

 stance always involves the reduction of another. In the first of 

 the two preceding formulas, the sugar is oxidized and the oxygen 

 reduced; and in the second, the carbon is reduced and the oxygen 

 oxidized. If oxidation and reduction processes are analyzed 

 more carefully, it is seen that what actually happens is an increase 

 in positive valence with oxidation and a decrease in positive 

 valence (or increase in negative valence) with reduction (this 

 is to be understood as involving only a change in the number of 

 valence electrons; reduction involves an increase, and oxidation 

 a decrease of electrons) ; thus : 



When iron in the ferric condition {e.g., as FeCls) is reduced 

 to the ferrous condition (FeCU), the metal gains a negative 

 charge (a decrease in the number of positive charges obviously 

 corresponds to a net increase in negative ones); thus: 



Fe+++ + H = Fe++ + H+ 



As the ion Fe++ is capable of losing an electron, it is regarded 

 as a reducing agent, or reductant; and as Fe+++ is capable of gain- 

 ing an electron, it is an oxidizing agent, or oxidant. The change 

 from one to the other is a reversible reaction and may be expressed 

 thus: 



Fe+++ + electron ^ Fe++ 



An important distinction lies between the oxidation of Fe++ 

 and the oxidation of sugar in metabolism ; the former is reversible, 



