174 RALPH S. LILLIE. 



tial reactions occur are thus spatially distinct and the processes 

 can be investigated separately. But evidently immersion of the 

 conducting wire in the solution does not alter the conditions in 

 any essential way. A piece of metal completely immersed in an 

 electrolyte-solution, and of different composition or solution- 

 tension at any two regions, or in contact at two areas with dif- 

 ferent solutions, is equally the seat of chemical change which is 

 associated with the passage of an electric current between the 

 two regions. This is the arrangement which corresponds more 

 obviously to the conditions usually met with in nature. The 

 case of local rusting in iron, or of the transmission of chemical 

 influence (e. g., excitation) from one region of a cell to another, 

 exemplifies such an arrangement. It is important not to allow 

 our conceptions of natural processes to be limited by the pecu- 

 liarities of laboratory devices; these are always more or less 

 arbitrary, and designed not only for convenience and reduplica- 

 tion at will, but with the special purpose of isolating the phe- 

 nomena and making them as sharply defined as possible. In 

 unmodified nature such conditions are rarely found; hence such 

 resemblances as that between local chemical action in metals 

 and the physiological effects following local alteration in living 

 cells are not easily recognized. 



LI iNi Sl-l >T - 



CTvf 



FIG. i. In this diagram medium M represents the metallic part of the circuit, 

 e. g., a platinum wire, medium E the adjoining electrolyte solution, e. g., NaCl. 

 Ferrous chloride is in contact with the wire at one end (.4), chlorine at the other 

 (B). The arrows show the direction of the electrical current (positive stream) in 

 the circuit. 



A simple type of oxidation and reduction cell seems best 

 adapted to illustrate the essential nature of the phenomena 

 under consideration, especially since the energy of vital processes, 

 including that of the bioelectric currents, is usually derived from 

 oxidations. Probably the simplest case is that of an easily 

 oxidizable salt, e. g., ferrous chloride, in contact with a chemically 



