PHYSIOLOGY OF THE INVERTEBRATA. 335 



The mean of these eight determinations is 5*95 metres, or 

 in round figures 6 metres, per second. 



The motor nervous excitation is transmitted, then, with 

 infinitely more slowness in the lobster than in the frog or 

 7nan. 



In Fig. 6^ the distance AC, which separates the beginning 

 of the curve CD from the point A, corresponds to about 

 500ths of a second. This duration represents the sum of 

 the two periods: ist, the time which is lost from the excita- 

 tion produced at the point a to run the length of the nerve as 

 far as the termination of it in the muscle ; and 2nd, the time 

 of latent excitation of the muscle. The latter is known and 



Fig. 67. — A Gkaphic Tracing kok Determining the Rate ok 

 Transmission oe Motor Excitation. 



A = moment of excitation of nerve. CD = curve of contraction obtained by 



the excitation of the nerve at n (Fig. 63). EF = curve of contraction ob- 



tained by the excitation of the nerve at b (Fig. 63). (Hundredths of a second.) 



determined, among other things, upon the same muscle. It 

 suffices to obtain a graphic tracing of the muscular contrac- 

 tions by directly placing the exciting electrodes upon the 

 flexor muscle of the dactylopodite. This time was found to 

 be i.500ths of a second, and that it did not exceed 200ths of 

 a second. There remained, then, at least 5 - 2 = 300ths of a 

 second, which represented the necessary time for the motor 

 excitation to travel from the point a along the nerve to the 

 interior of the muscle. The length of this portion of the nerve 

 could not be directly determined ; but it was very probably 

 less than 500ths in these experiments, and did not certainly 

 reach 1 000th. That gave a velocity of 1.66 m. per second in 

 the first hypothesis, and 3.33 m. in the second. From these 



