50G 



Mr. K. Lucas. 



[June 6, 



reduced to minimal intensity within the cooled region (where recovery from 

 the effects of the first disturbance would be slow), and grew up to full 

 dimensions again when it emerged into the warmer stretch of nerve. In 

 fact, we are attempting in such experiments as these to study the parallelism 

 between two phenomena, of one of which we can obtain a relative measure 

 only down to certain unknown limits of smallness, while of the other we can 

 make no relative measure at all — we can, in fact, only assert with some 

 probability that it is present or not. 



On these grounds, in the ultimate resort, I believe every attempt to show 

 directly a want of parallelism between the propagated disturbance and the 

 electric response has been wrecked. Must we, then, abandon the attempt to 

 enquire by direct experiment whether changes in the electromotive force of 

 the electric response do run parallel to changes in the propagated disturbance ? 

 There is one possible method, and, as far as I can at present see into the 

 matter, only one, by which it is possible to obtain a relative measure of the 

 propagated disturbance, that is to measure it in terms of the only property 

 which we can assign to it without unwarranted assumption, its ability to 

 propagate itself. It is this method which Adrian and I used when we were 

 trying to measure the effect upon a propagated disturbance of the time- 

 interval separating it from a predecessor which had passed along the same 

 path. We found that the shorter the interval the less was the distance 

 which the second disturbance could travel without extinction through a 

 tract of nerve in which it was undergoing a decrement. The essence of the 

 method is to set the disturbance, whose intensity is to be measured, at 

 a region of nerve where conduction is impaired, and to determine whether it 

 is there capable of travelling as far as a full normal disturbance could travel. 

 A comparison of the distance travelled by the disturbance under test with 

 the distance travelled by the normal disturbance gives a measure of the 

 relative intensity of the former. Another example of the method is its use 

 in the work of Adrian on the recovery of a disturbance after it has emerged 

 from a tract of nerve where it has been undergoing a decrement. His 

 method was to lead it, after it had emerged clear from one such tract, into a 

 second, and to see whether it was as successfully propagated through the 

 second tract as was a fresh disturbance which had not faced the first 

 tract at all. 



This is a possible method of obtaining the measure which we need. 

 Whether the future solution of our problem will rest on the laborious 

 accumulation, by some such method, of evidence that the electric response 

 and the propagated disturbance are indissolubly bound together, cannot be 

 foretold. Up to the present the available evidence does not contradict the 



