1902.] Photographic Records of the Response of Nerve. 217 



second exactly equals the distance between the leads, they neutralise 

 each other, and the electrometer only records the electro-positive 

 (first phase) of the first wave and the electro-negative (second phase) 

 of the second, fusing them into a single response. 



For the electrometer indicates in every case merely the algebraic 

 sum of all the potential differences existing at any instant between the 

 two leads. 



Development and Subsidence. 



Flat-topped curves are particularly valuable for determining the 

 rates of development and subsidence of the electromotive condition at 

 any given point on the nerve. 



It is, however, necessary first to ascertain to which of the two 

 classes mentioned above, the curve belongs. 



(A.) Let the length of the wave be greater than the distance 

 between the leads and let all the linear conductors pass under 

 both leads. 



Then both the beginning and the end of the first or electro- 

 positive phase will be due to the wave front — passing first 

 under the proximal and then under the distal electrode. The 

 first phase of the photographed curve will therefore be sigmoid 

 with the two ends similar as in fig. 16, a, and the analysis of 

 it will be of the type shown in fig. 16, b, that is to say, sym- 

 metrical. 



The second or electro-negative phase will be due entirely 

 to the subsidence of the electromotive condition, first at the 

 proximal lead, giving the beginning of the second phase, and 

 then at the distal lead, corresponding to the end of the 

 curve. 



This phase also will be sigmoid with the two ends similar. 

 The shape of each end will depend on two functions, one of 

 which, / (p), representing the distribution of the points of 

 origin, is common to both first and second phase ; but the 

 other, / (k, tt), the rate of subsidence, is peculiar to the 

 second phase. 



I have come to the conclusion that in the great majority 

 of cases the curves indicate a slower rate of subsidence than 

 of development. The second phase of the photographed 

 curve may therefore have under these conditions the form 

 shown in fig. 16, c; and its analysis will be represented by 

 fig. 16, d. 



(B.) The second class of curve is produced when the length of the 

 wave is less than the distance between the leads. In this 

 case the beginning of the first phase and the beginning of 



