ELECTROPHYSIOLOGY 345 



pounds on opposite sides of the membrane (oxidation-reduction 

 reactions at membrane surfaces are known as eledrostenolysis). 

 In such cases, where electrons are lost from oxidized molecules 

 and in some way an equivalent number of electrons reach the 

 reduced molecules oh the other face of the membrane, there 

 must, it would seem, be a combination of electrolytic and 

 electronic conduction. Lillie has suggested that carbon chains 

 may serve as electronic conductors in living systems. 



If we conclude that potential is a measure of the level of free 

 energy and that the voltage registered by a potentiometer 

 measures simply a tendency for electrons to go from one place 

 to another {i.e., voltage is the intensity factor of energy), we do 

 not thereby deny the presence of those phenomena in living 

 systems which involve an actual transfer of electrons during the 

 course of an oxidation-reduction reaction. This is the case of 

 nerve conduction (page 335), which is a wave or series of waves of 

 oxidation and reduction. Here there is a dynamic process involv- 

 ing chemical reactions in which electrons may be moving. The 

 chemical reaction requires a flow of electrons in order that it 

 may take place; the potentiometer measures the tendency to 

 flow. 



A mixture of ferrous and ferric chloride in an electrode vessel 

 will yield an oxidation-reduction potential. It is usually 

 expressed in volts with reference to the normal hydrogen elec- 

 trode, the potential of the latter being taken as zero. Two fac- 

 tors primarily determine the magnitude of oxidation-reduction 

 potentials— the ratio of oxidant to reductant and (in most 

 organic systems) the activity of the hydrogen ion. 



Oxidation-reduction potentials are of the order of 1 volt, 

 varying from less than the -|-0.2 volt of the system Cu+/Cu++ to 

 more than the -f- 1.8 volts of the system Pb++/Pb++++. (Temper- 

 ature is a factor.) 



Oxidation-reduction Potentials in Living Systems. — The 

 measuring of the oxidation-reduction potential of Uving cells 

 usually consists in bathing the cells in, or injecting into cells, 

 color indicators covering the scale of potential values from that 

 of the hydrogen electrode to that of the oxygen electrode. The 

 dyes are taken in sequence, and their reactions observed in the 

 cell. A dye, such as methylene blue, will be oxidized (and 

 retain its color) or reduced (and lose its color) depending upon 



