110 TRANSMISSIVITY IN PASSIVE IRON WIRES 



have been considered. It seems probable that the presence of a 

 brief "absolute," preceding a longer "relative," refractory phase is 

 an index of the existence of two distinct stages or processes in the 

 reconstitution of the plasma membrane, the first stage preceding and 

 the second succeeding the recovery of semipermeabiHty. This view, 

 however, accords imperfectly with Tait's special hypothesis that the 

 "absolute" refractory period corresponds to the period of upstroke of 

 the bioelectric variation, and the "relative" period to the return phase. 

 In the metallic model the change of potential accompanying repassi- 

 vation, i.e. the return phase of the whole electrical variation associ- 

 ated with the local reaction, is a definite index of the reformation of 

 the passivating surface film of oxygen compound. This process oc- 

 curs rapidly; but it is not until the lapse of a considerable time (usu- 

 ally some minutes) after its completion that the condition of the film 

 becomes such as to permit again of ready and complete transmission. 

 Evidently some further change in the newly restored film is necessary 

 for a return of its original properties ; and it seems probable that in 

 the living system closely comparable conditions may obtain. It is 

 certain that the relative refractory period greatly outlasts the return 

 phase of the bioelectric variation in many cases. 



In the living irritable element there is evidence that stimulation is 

 associated with a temporary alteration or breakdown of the proto- 

 plasmic surface film or plasma membrane, involving a general in- 

 crease of permeability.* Stimulation follows any sufficiently rapid and 

 extensive change in the electrical polarization of the semipermeable 

 protoplasmic surface, or any sufficient local mechanical or chemical 

 alteration; such a change, even though purely physical in itself, ini- 

 tiates a chemical disturbance, associated with a variation of potential, 

 which sweeps over the cell surface, and apparently consists essentially 

 in a wave of alternate dissolution and reconstruction of the surface 

 film. This "propagated disturbance"^ is the condition for the release 

 of the chemical and other activities in the cell interior which constitute 



* For a brief summary of this evidence cj. Lillie, R. S., Am. J. Physiol., 1915, 

 xxxvii, 356. Further references there given. 



^ Keith Lucas' term, to distinguish the transmitted effect from the local or 

 initiatory effect produced by the stimulating agent. For the experimental basis 

 of this distinction c/. Adrian, E. D., and Lucas, K., /. Physiol., 1912, xliv, 68. 



