1902.] Photographic Records of the Response of Serve. 



197 



the sum of two functions — one representing the development and the 

 other the subsidence of a wave of electromotive force passing along it. 

 Having thus dealt with the single linear conductor, the more complex 

 case of a bundle of conductors may be expressed as the sum of a 

 number of similar functions with different constants. 



But although this method of proceeding is convenient for examining 

 the experimental results, it only represents indirectly the facts which 

 it is our object to investigate. 



The real problem may be stated thus : Conceive three similar con- 

 secutive short portions, A, B, C, of a single nerve fibre, such that each 

 of them may be regarded as a complete element of the fibre ; it is 

 required to determine — 



1. The development, duration, and subsidence of the electrical 



changes in either of them. 



2. Those conditions in B which enable it to become active under the 



influence of A. 



3. Those conditions in B which enable it to induce a state of 



activity in C. 



It will be observed that 1, 2, and 3 enter simultaneously into almost 

 every possible experiment, but may be separately investigated by two 

 distinct methods, namely, the physical — e.g., alteration of position of 

 leads, exciting electrodes, &c. — and the physiological — e.g., influence of 

 temperature, electrotonus, reagents, injury, &c. But whether the 

 method be physical or physiological, the analysis of the photographic 

 record merely gives the sum of the electrical changes occurring between 

 two fixed electrodes at any given moment, so that in either case the 

 analysis itself has to be interpreted in order to show how the curve is 

 to be explained in terms of 1,2, and 3. 



It will be observed that no assumptions are made either as to the 

 cause of the electrical phenomena, or the mode in which they are 

 related to the activity of the tissue, beyond the fact that there is in 

 muscle or nerve a potential gradient between a part in a state of 

 physiological activity and neighbouring parts at rest. The E.M.F. 

 might, so far as this investigation is concerned, be a function of the 

 active condition, or of the transition from one state to another. In 

 either case the method of dealing with the records would be the same. 

 But having ascertained the meaning of the records, it may be possible 

 by comparing them to determine whether the electrical changes are 

 essential, or merely concomitant phenomena, of the active state. 



