1902.] Photographic Records of the- Response of Nerve. 207 



hence pa - vh = d marks the beginning of the difference of potential, 

 and this gives h = 0. It should be noted that, as in the previous case, 

 if any two similar conductors have their points of origin of E.M.F. 

 situated at equal distances on either side of the middle point between 

 B and D they will neutralise each other, and thus reduce the total P.D. 



B p p I) 



P n 



Pig. 10. — As in Fig. 9. B, D, electrometer leads. P L . . . . P„, points of origin. 



In fig. from its position would add nothing to the P.D. until 



the wave-front starting from it had reached D on the one side. But 

 its effect would cease the moment the opposite front of the wave 

 reached B. The maximum would therefore be as intense as with all 

 the points of origin outside the leads, but it would last a shorter time 

 and appear to develop more slowly. 



In this connection it may be observed that the form of the rise of 

 potential difference between the leads B and A gives the distribution 

 •of the points of origin pi, p- 2 , p-z, . . . . in the bundle, whereas the form 

 of the rise of potential difference for the leads C and D gives the 

 •distribution of p n , p n -i, pn-2, &c. 



Furthermore, it is evident that the curve of the second phase, in all 

 •cases where the leads are far enough apart, must be a repetition, 

 reversed, of the curve of the first phase, so far as it is conditioned by 

 the distribution in the bundle of the points of origin, and that any 

 •difference between the first and second phases must be due either to 

 interference through overlapping or to some difference, general or 

 local, in the time relations of the development and subsidence of the 

 wave of electromotive force, or of its rate of propagation. The 

 .analyses show that such a difference exists. 



B. Influence of the Rate of Development and of Subsidence of the E.M.F. at 

 a Given Point of each Conductor in the Bundle. 



The possibility that the development of the E.M.F. at successive 

 points of a single linear conductor may not be sudden but gradual, 

 must also be taken into consideration. 



The effect as regards the time relations of the difference of potential 

 at the leads is in the main similar to that produced by a bundle of con- 

 ductors in which the points of origin of the wave of electrical change 

 are distributed over a definite portion of its length. 



If the circumstances are such that the distribution of the points of 

 origin cannot be determined, and if there is no means by which the 

 electrical activity can be caused to originate at some definite point of 



