1902.] Photographic Records of the Response of Nerve. 



203 



But by observation it is found that the first electrical change (in the 

 case of muscle or nerve) is followed by a second in the opposite direc- 

 tion, and therefore we are justified in assuming that the subsidence of 

 the condition of activity in the case of muscle and nerve takes place 

 first at the point at which it originated. 



We may therefore designate the position in the linear conductor of 

 the wave-front of cessation from the active condition by an expression 

 of the form, 



x 1 = ])±i'i(t+6), 



where 6 represents the duration of electrical activity in the portion of 

 the linear conductor under P. If the central portions of the linear 

 conductor remain active longer than those nearer the ends, then 

 v 1 >v. If the period of activity becomes longer as the ends are 

 approached we must have i\ < v. 



But if under normal conditions each portion of the linear conductor 

 becomes active to the same degree, and for an equal period, then 

 v 1 = v, and the progress of the wave of electrical activity must be 

 represented by two parallel curves, one indicating its development and 

 the other its subsidence for successive points along the linear conductor. 



Hence in the normal case now under consideration we may put 

 V\ = v. Then, between the leads A and B, B becomes negative to A 

 when the wave of cessation 



X\ = p - v (t - 0) reaches B, i.e., when 

 h' = (p-b + v$)/v, 

 and remains negative to t until the wave-front reaches A, i.e., when 

 U = (p-a+v6)/r. 

 The duration of the P.D. is as before 



t-y' - t{ — (!) - a)jv, 



the two waves differing only by a time-constant 6. 



Taking now the combined effect of both waves, it is evident that 

 the form of the resulting curve of P.D. must depend upon the relation 

 between and (b - a) /v. 



If (b - a)/v is less than 6 then the first phase of the effect upon the 

 leads A and B will be over before the second phase begins, and there- 

 fore there will be an interval of 1^0 - ^LzSJ^j between them during 



which the P.D. will be zero. 



If (b - a)/v = 6 then the first phase will be succeeded by the second 

 phase with no interval between. 



If (b - a)jv is greater than d then the second phase starts before the 

 first is over, but being of opposite sign, and ex hypothesi equal in 



