POLAR EFFECTS OF ELECTRICAL CURRENT 205 



records should be equal to the time taken by excitation to 

 travel the intervening distance of 12*5 mm. between the 

 electrodes. This time-interval should be equal to ^ s ; 

 where V is the velocity of transmission in the given specimen- 

 The velocity can easily be deduced from the two records 

 themselves. From the upper record we see that response 

 took place after 8 spaces, each representing one-twentieth 

 of a second. The true time taken by stimulus to traverse 

 the distance of 2-5 mm. is therefore /o— L; where L is the 



Fig. 109. — Records of responses to ascending and descending make 

 currents in Mimosa. In the upper record the current was 

 descending, kathode being proximal to pulvinus. In the 

 lower record the current was ascending, kathode being 

 distal. Frequency of vibrating recorder 20 D.V. 



latent period of the pulvinus, the average value of which we 

 found to be - i second ; hence V = " = 8-3 mm. per second. 

 From the second record we find the true time taken by 

 excitation to traverse the distance of 15 mm. to be 1/8 — L 

 = 17 second. V = T '.| = 8*8 mm. per second. The mean 

 velocity obtained from the two records is therefore 8-6 mm. 

 Hence the difference of time in the two cases of excitation by 

 ascending and descending current should be equal to the 

 time taken by the excitation to travel 12*5 mm. the distance 

 between the two electrodes. This difference should there- 

 fore be ^| = 1 -4 second. That this is really the case 

 can easily be tested by the simple process of counting the 



