78 STUDIES IN ELECTRO-PHYSIOLOGY: 



"It is interesting to state, if only in outline, the kind 

 of theories which are in the air at present. We must 

 await with patience to see whether they or any of them 

 contain a germ of truth, or whether, like so many theories 

 in the past, they will be forgotten in the future." (Halli- 

 burton, 1915.) 



That is tantamount to a confession that the chemical 

 theory is not altogether satisfying. Once, however, we 

 understand the law, our knowledge of the full application 

 of it will only involve some further microscopic and 

 galvanometric research, with our eyes wide open, to find 

 the something which exists but which we have not seen, 

 for the simple reason that we have not been taught to 

 look for it. 



In regard to the analogy with muscle it must, I think, 

 be admitted on the face of the evidence I shall bring 

 forward that the structure and operation of voluntary 

 muscular fibre offers a very strong proof that muscular 

 impulse is primarily due to the propagation of neuro- 

 electrical, and not chemical, disturbances. I cannot, in 

 fact, find any physiological argument which is not more 

 in favour of electrical than of chemical action. Explana- 

 tion of the latter is often laborious and unconvincing, 

 whereas the former is always and in every detail 

 harmonious. 



The velocity of the nerve impulse in man is said to be 

 about 120 metres per second. Now, the apparent velocity 

 of an electrical current is diminished more or less in pro- 

 portion to the capacity of the circuit ; the higher the 

 capacity the lower the velocity, due to retardation. 

 A cable is a homogeneous structure, in the sense that in the 

 circuit of which it forms a part there are no, or very few, 

 " synaptic junctions " to occasion delay. 



In the human body the velocity of the nerve impulse is 

 not everywhere the same, nor could it be so unless the 



