1912.] The Process of Excitation in Nerve and Muscle. 509 



which had only been traversed by the propagated disturbance which the first 

 , stimulus had initiated. This fact Bramwell and I have confirmed,* and there 

 seems to be real evidence that the refractory state is a consequence of the 

 passage of the propagated disturbance, and not a local effect. The delay of 

 propagation was ascribed by Gotchf to both factors, the propagated change 

 and the local effect. His evidence on the latter point was that prolonged 

 stimulation of a nerve brought the seat of excitation into a condition which 

 delayed the propagated disturbance. On attacking experimentally the relative 

 importance of the two factors, in so far ,as they enter into the effect of a single 

 stimulus, I found that the delay was practically identical whether the second 

 stimulus did or did not fall on the same point as the first.t From this 

 •experiment it follows that the delay observed in such a case is a consequence 

 of some change left behind in the tissue by the propagated disturbance as 

 such. It would seem that the local effect which Gotch described does not 

 enter normally into the delay, being only a consequence of such prolonged 

 stimulation as produces some abnormal alteration of the tissue. The delayed 

 propagation falls therefore into line with the refractory state as part of the 

 process of recovery from some change associated with tbe propagated 

 disturbance. The third phenomenon, the reduced size of the propagated 

 •disturbance elicitable during recovery, does not seem yet to have been 

 assigned experimentally to its position, but the close parallelism of its 

 progress in time§ with that of the refractory period is strong evidence 

 that both are aspects of one process of recovery. 



The sum of this evidence is that in all these phenomena of impaired activity 

 we have expressions of a single process of recovery from some change which 

 is associated with the propagated disturbance. From what change precisely the 

 ■tissue is recovering we do not yet know. It seems very probable that in 

 these phenomena w e measure the actual return of the tissue to the equilibrium 

 position after its disturbance by that change which is the basis of propagation. 



The most definite attempt to relate the refractory state to the progress of 

 other phenomena of activity has been that of Tait.|| He starts from the 

 observation which many experimenters have made, that there is a general 

 association between the duration of the refractory period and that of the 

 electric response, tbe two phenomena changing together as we pass from 

 tissue to tissue, or from one condition to another. Beyond this he points 



* Bramwell and Keith Lucas, 'Journ. Physiol.,' 1911, vol. 42, p. 495. 

 J Gotch, loc. cit. 



t Keith Lucas, Mourn. Physiol.,' 1910, vol. 41, p. 400. 



§ Adrian and Keith Lucas, ' Journ. Physiol.,' 1912, vol. 44, p. 93. 



|| Tait, 1 Quart. Journ. Exp. Physiol.,' 1910, vol. 3, p. 221. 



