524 ' The Process of Excitation in Nerve and Muscle. 



very fact that we have been concerned so largely with the gaps in our 

 knowledge is, I believe, a hopeful sign. 



Perhaps it is another sign of the same progress that we no longer hope to 

 capture the nervous impulse by storm, but have set persistent siege to its 

 outworks. It is because the outworks show signs of yielding that we are 

 a little nearer to understanding the nervous impulse, though we have as yet 

 formulated no hypothesis of its intimate nature. In our analysis of the 

 phenomena concerned with propagation we did, in spite of conspicuous 

 difficulties, find that there was a clear definition of the range of phenomena 

 which must be taken into account. Nor must we overlook the importance 

 of that step which led us to recognise the local excitatory process. In the 

 physico-chemical identification of that process there seems to lie before us 

 the next stage of our progress. In Nernst's hypothesis of the nature of local 

 excitation it is my belief that we have a means of attack which is quite 

 invaluable. It is not a complete theory, ready, or even approximately ready, 

 for acceptance, but it is an indispensable guide to the strengthening of our 

 experimental data, and so to the ultimate elaboration of an hypothesis which 

 shall be free from those difficulties which are at present so obvious. Our 

 concern in the immediate future must be with quantitative experimental 

 work. The ultimate hypothesis to which such work shall lead may perhaps 

 be very near to that which Nernst has stated. On that point it would be , 

 idle to speak at present. However that may be, when a wholly satisfactory 

 theory of the local excitatory process is in our hands we shall have a new 

 weapon of attack upon the physico-chemical nature of the nervous impulse. 



And it is not only in this preliminary work on the local excitatory process 

 that the hope of new progress springs from a closer definition of our 

 ignorance. In direct work upon the central problem of the propagated 

 disturbance the same is true. I have tried to show you how, in our work 

 upon the phenomena of propagation, we have been hampered because we 

 could get no quantitative measure of that disturbance, and I have attempted 

 to discuss the possibility of obtaining such a measure in the future. We 

 shall have made some progress to-day if we have done no more than realise 

 the importance of that gap in our knowledge. For whenever the time shall 

 come for the formulation of definite hypotheses of the propagated dis- 

 turbance, it can hardly be doubted that the work of verification will rest in 

 large measure, as it does in the case of every scientific hypothesis, on the 

 comparison of calculated inferences with the results of quantitative measure-: 

 ment. 



