344 PROTOPLASM 



mechanism for purposes of thermodynamic formulation, provided 

 that it does not violate the fundamental postulates of thermo- 

 dynamic theory. Our postulates give no clue as to which of the 

 mechanisms is the actual one. Because we utilize some of the 

 free energy by means of a platinum electrode and thus produce 

 an electric current that can be measured, this does not imply 

 that an electric current is produced in the system. In other 

 words, we measure and express the level of free energy in terms 

 of an electric potential simply because the potentiometric method 

 is usually the most convenient one for measuring the difference 

 in energy level. We could just as well express the free energy 

 in terms of a different scale — say, for instance, in terms of 

 calories. 



Although the method of measurement, rather than the system 

 itself, may give rise to electric potentials, yet, as there is a 

 decrease in the level of free energy, conduction by means other 

 than direct electron conduction may take place, viz., by electro- 

 lytic conduction. The experiments of R. LilUe (page 335) 

 give further support to the possibility that an actual flow of 

 current takes place in Hving systems. There is a great similarity 

 between the flow of current along (the surface of) an iron wire 

 immersed in an electrolytic solution and the conduction of an 

 impulse along a nerve. As this similarity is very pronounced, 

 there may yet be something within the nerve that is analogous 

 to the metal. LiUie has himself considered this possibility and 

 appears to be of the opinion just stated, viz., that there are regions 

 in hving tissues at which oxidation and reduction occur in 

 dependence on a flow of current and therefore on metalhc or like 

 conductors. In the comparison with the condition in passive 

 iron, it is assumed by Lillie that the oxide film behaves in a way 

 similar, in a general electrochemical sense, to that of the plasma 

 membrane of the irritable Hving element. Oxidation occurs at 

 one region simultaneously with reduction at another region at 

 some distance, and the associated structural changes involve 

 changes of potential of such a kind that the effect is automatically 

 transmitted. We do not know if there is anything in the nerve 

 to correspond to a metal electrode or conductor, but the essential 

 factors are the same in the iron and in the nerve. 



Chemical reactions occur on the passing of a current across a 

 membrane in contact with solutions containing reactive com- 



