RALPH S. LILLIE 111 



the response to stimulation. Normally in a highly irritable element, 

 such as a muscle cell or nerve fiber, the whole cell surface is thus in- 

 volved, hence the "all or none" character of the response; but the 

 passage of the excitation wave, and with it the local response, can be 

 interfered with or prevented by various artificial conditions (narcosis, 

 electrotonus, local chemical or mechanical conditions). There are 

 many purely physiological indications that the transmission of exci- 

 tation from one region of the conducting element to the next adjoin- 

 ing is due to the local bioelectric variation resulting from this surface 

 alteration.^ The reference of the bioelectric variation to a local 

 change in the physical and chemical character of the cell surface, 

 which apparently acts like an electrode of variable chemical composi- 

 tion and potential, is consistent with what we know of the conditions 

 in various inorganic systems exhibiting an analogous type of beha\'ior; 

 examples of such systems are mercury in hydrogen peroxide,^** chro- 

 mium and other electrodes exhibiting rhythmical changes of potential,^i 

 and especially metals in the passive state, more particularly iron.^^ 



Activation and transmission in passive iron are due to alterations 

 in the continuous or impermeable^^ surface film of oxidation product 

 covering the surface of the metal. On account of the extreme thin- 

 ness of this film, the surface of the passive metal, in its property as 

 an electrode, is highly variable and sensitive to mechanical or other 

 disturbance. The susceptibility of a passive iron wire to activation 

 by mechanical and chemical agents and by the electric current (when 

 the metal is made cathode) is thus readily explained. Interruption 

 of the film produces a local circuit, and electrolyses at the electrode 

 areas of this circuit — ^reduction at the cathodal and reoxidation at the 

 anodal areas — are responsible both for the rapid extension of the ac- 

 tive area (transmission) and for the automatic return to the passive 



^"Bredig, G., and Weinmayr, J., Z. physik. Cheni., 1903, xlii, 601. Bredig, 

 G., and Wilke, E., Biochem. Z., 1908, xi, 67. Von Antropoff, A., Z. physik. Chetn., 

 1908, Ixii, 513. 



" Ostwald, W., Z. physik. Chem., 1900, xxxv, 33, 204. 



^^ The general article by Bennett and Burnham (Bennett, C. W., and Burn- 

 ham, W. S., /. phys. Chem., 1917, xxi, 107) gives a full account of the phe- 

 nomena of passivity in metals and an exhaustive literature list. 



^^ /. e. impermeable to acid, hence its protective influence. 



