ISO RALPH S. LILLIE. 



be briefly considered, although for the present little more can 

 be done than to indicate the probable class to which the phe- 

 nomena belong; the elucidation of details is a task for future 

 research. In general the film separating the protoplasm from 

 the external medium is thin and semipermeable, and the solu- 

 tions on either side of this partition are of different composition. 

 Hence the conditions for a potential-difference between proto- 

 plasm and medium exist; and such a state of electrical surface- 

 polarization is always found. This polarization varies char- 

 acteristically with the nature and the physiological activity of 

 the cell; and circuits are thus continually arising in active 

 tissues (like muscle, nerve, etc.) between different regions of the 

 cell-surface. The conditions under which the normal bioelectric 

 circuits originate seem most closely analogous to those prevailing 

 in such an arrangement as the "oxygen-hydrogen cell " of electro- 

 chemistry, in which two platinum electrodes, charged respec- 

 tively with oxygen and hydrogen, are immersed in an electrolyte- 

 solution. In this case the oxygen electrode forms the cathode, 

 the hydrogen, the anode; the oxygen gives up positive charges 

 to the platinum when the circuit is closed, while the hydrogen 

 receives such charges from the metal; the oxygen thus forms 

 oxygen- or hydroxyl-ions, the hydrogen forms hydrogen-ions; 

 and the union of these to form water furnishes the energy of the 

 current. Let us suppose to make the case concrete that the 

 external solution bathing the living cell contains oxygen, and 

 that the surface-film consists of oxidizable material. In the 

 resting condition of the cell there is a certain tendency for the 

 oxidation to take place (or oxidation-tension), i. e., for the oxygen 

 to impart positive charges to the oxidizable partition, becoming 

 itself ionized; but this tendency is held in check just as in the 

 oxygen-electrode when the circuit is open because such a trans- 

 fer would leave unbalanced negative charges behind in the 

 medium. Hence an equilibrium exists, similar to that at the 

 surface of any battery-plate with open circuit. But any change 

 of condition by which negative charges may be set free in the' 

 protoplasm at any region will disturb this equilibrium and allow 

 the combination to take place. The oxygen then imparts its 

 positive charges to the oxidizable material of the partition ; this 



