VELOCITY OF TRANSMITTED IMPULSE 135 



For successive determinations, with the same specimen, 

 of the periods required for the transmission of excitation 

 through a given length of conducting-tissue, did not differ 

 from each other by so much as one-twentieth of a second 

 and were often actually identical. 



Determination of Velocity of Transmission 



For the purpose of these experiments I used by prefer- 

 ence the petiole of Mimosa, for the reason that in this the 

 conducting-strands situated in the fibro-vascular bundle 

 would be more continuous and evenly distributed than in 

 a branching specimen. In order to determine the velocity 

 of transmission, the stimulus of induction-shock is applied 

 to the petiole at a distance d from the responding pulvinus. 

 Let us suppose t to be the true time taken by the excitation 

 to reach the pulvinus ; the initiation of the responsive 

 movement will however be further delayed by the latent 

 period of the pulvinus L. The total time-interval T observed 

 to elapse between the application of stimulus and the 

 initiation of response will therefore be the true time t plus 

 the latent period L. To obtain the true time we have to 

 subtract the latent period L from the observed interval T, 

 thus t—T— L. The velocity of transmission is then found 

 by dividing the distance by the true time. The necessary 

 data are therefore the distance between the stimulated 

 point and the pulvinus, the time-interval between the 

 application of stimulus and the initiation of response, and 

 the latent period of the individual pulvinus. 



In making these determinations the apparatus employed 

 is the same as that for the determination of the latent 

 period. As in these experiments we have to measure 

 time which may be several seconds in duration, the record- 

 ing-plate is made to travel at the relatively slow rate of 

 2 cm. each second or thereabouts. The vibrating recorder 

 must be selected according to the degree of accuracy that 



