1912.] The Process of Excitation in Nerve and Muscle. 501 



too weak to be effective, will succeed in setting the propagated disturbance 

 in motion. It is clear that some change persists in the nerve after the first 

 current has ceased to flow, and renders effective the otherwise inadequate 

 second stimulus. The important question from the analytical standpoint is 

 whether this persisting change is merely a quantitatively less intense 

 disturbance of the same nature as that which is the basis of propagation^ 

 or is an incomplete preliminary process which needs to be of greater 

 intensity before the propagated disturbance can be initiated at all. The 

 evidence on this point seems to establish clearly the fact that the latter 

 alternative is correct; we have to do with a preliminary change. In the 

 first place Adrian and I found that there was no measurable trace of this 

 change being propagated from the seat of the first stimulus.*" Also it must 

 be noticed that whereas the persisting after-effect of the inadequate first 

 stimulus is that the tissue can be excited by a weaker stimulus than other- 

 wise, the effect of an adequate stimulus on a nerve is that for a considerable 

 period a second stimulus will either be unable to excite at all, or will need 

 to be considerably strengthened, these being the phenomena of the refractory 

 state which Gotch and Burchf first detected in nerve. It is scarcely- 

 probable that the same disturbance should so invert its after-effects by 

 undergoing itself no alteration but a change of intensity. And the evidence 

 in favour of these divergent after-effects belonging to two distinct stages in 

 the setting up of the propagated disturbance becomes far stronger when we 

 examine the effect of temperature change on the persistence of the after- 

 effects of adequate and inadequate stimuli. It was shown by Bazettj that 

 a fall of temperature from 18° C. to 8° C. prolongs the time of persistence of 

 the lowered excitability following an adequate stimulus by about 200 per cent.. 

 The heightened excitability which follows an inadequate stimulus I found§ to 

 be prolonged under a like change of temperature by less than 40 per cent. 

 The outcome of this evidence I think is clear. We have in the summation 

 of inadequate stimuli proof of the existence of a local change which must be- 

 brought about with a certain intensity by the stimulating current before ftie 

 propagated disturbance can be started. I have called this change the local' 

 excitatory process. We shall return presently to examine it more closely, 

 and shall see how a knowledge of its nature is essential to auy hypothesis of 

 the propagated disturbance because it is the middleman between that 

 disturbance and the external stimuli which we can control experimentally. 



* Adrian and Keith Lucas, loc. cit. 



+ Gotch and Burch, ' Journ. Physiol.,' 1899, vol. 24, p. 410. 

 \ Bazett, 'Journ. Physiol.,' 1908, vol. 36, p. 426. 

 § Keith Lucas, 'Journ. Physiol.,' 1910, vol. 39, p. 469. 

 VOL. LXXXV. — B. 2 N 



