492 



Prof. J. C. Bose. Influence of Electric 



of response. The total time is therefore 1*7 seconds, and by subtracting from 

 it the latent period of 01 second we obtain the true time, 1*6 seconds. The 

 normal velocity is found by dividing the distance 15 mm. by- the true interval 

 1*6 seconds. Thus V = 15/T6 = 9*4 mm. per second. We shall next 

 consider the effect of current in modifying the normal velocity. The upper- 

 most record (1) in fig. 3 was taken under the action of a heterodromous 



Fig. 3. — Eecord showing enhancement of velocity of transmission induced by hetero- 

 dromous (uppermost curve) and retardation of velocity induced by homodromous 

 (lowest curve) currents. N, normal record in the absence of current. — indicates 

 heterodromous, and — » homodromous current. 



current of the intensity of 1*4 microamperes. It will be seen that the time- 

 interval is reduced from 1*7 seconds to T4 seconds ; making allowance for 

 the latent period, the velocity of transmission under heterodromous current 

 Vi = 15/T3 = 1.1*5 mm. per second. In the lowest record (3) we note the 

 effect of homodromous current, the time-interval between stimulus and 

 response being prolonged to T95 seoonds and the velocity reduced to 8*1 mm. 

 per second. The conclusion arrived at from this mechanical mode of 

 investigation is thus identical with that derived from the electric method 

 of conductivity balance referred to previously. 



That is to say, the passage of a feeble current modifies conductivity for 

 excitation in a selective manner. Conductivity is enhanced against, and 

 diminished with the direction of the current. 



The minimum current which induces a perceptible change of conductivity 

 varies somewhat in different specimens. The average value of this minimal 

 current in autumn is 1*4 microamperes. The effect of even a feebler current 

 may be detected by employing a test stimulus which is barely effective. 



