1912.] The Process of Excitation in Nerve and Muscle. 523 



be found that formulae based on mathematical reasoning intended to cover 

 the case of such currents shall also fail. In the same category we must 

 probably place the question of condenser discharges and alternating currents. 

 Into these cases, though much work has been devoted to them, I have found 

 it impossible to enter without prolonging this discussion beyond all legitimate 

 bounds. The problem of slowly increasing currents and of the anodic 

 excitation prove, however, to be on a different footing. They not only call 

 for the postulation of a disturbing factor which need not enter into the other 

 cases, but are at present so weak in quantitative experimental work as to 

 render the verification of any hypothesis quite impossible. And lastly the 

 location of the membranes is a difficulty which has scarcely yet been faced. 

 If in this account I seem to have laid stress rather on the difficulties which 

 stand in the way of the hypothesis than on the measure of success which it 

 has already achieved, it is because I believe that by such treatment we may 

 best gain from the hypothesis the undoubted help which it has to offer, even 

 in its present stage of incompleteness. To disregard its difficulties would be 

 to reject the guidance which it can give to future experimental work. 



With this I reach the end of the story which it has been my endeavour to 

 lay before you. I am very conscious that within the compass of this lecture 

 I have been able to trace out but one of the many lines of work which are 

 converging towards an ultimate solution of the central problem, the physico- 

 chemical identification of the nervous impulse. In the investigation of the 

 colloidal state, to take but one example, there is much done already and 

 much more which needs to be done before even the formulation of a definite 

 hypothesis can begin. And yet even in the limited range of facts which 

 I have tried to recount I find a conviction that we can no longer repeat 

 truthfully the words of Biedermann which I have quoted. I do not find 

 that we are now as far as ever from an understanding of the intimate 

 nature of the nervous impulse. If I have been able at all to make my 

 meaning clear, you will have realised that we may now claim to have passed 

 through the first phase of ignorance, in which we merely admitted that we 

 did not know, and to have reached the second phase of ignorance, in which 

 we are recognising what precisely are the points on which our want of 

 knowledge is most profound. In treating of the analysis of the complex of 

 phenomena involved in excitation and conduction I found it necessary to lay 

 stress upon particular defects of our experimental knowledge. And again 

 when the hypothesis of Nernst was before us it was with its special 

 difficulties rather than its achievements that we were occupied. Its value 

 for the purpose of immediate work proved in fact to lie largely in its 

 detection of specific points of weakness in our experimental data. The 



