60 



ELECTRO-PHYSIOLOGY 



CHAP. 



the deflection in the former case will be greater. The difference 

 gives the time in which the excitation travels from the distal 



(central) to the proximal 

 (peripheral) point of exci- 

 tation. At a later period 

 Helmholtz arrived at the 

 same result by a simpler 

 method, i.e. the graphic 

 record of the muscle 

 twitches on stimulating 

 two points of the nerve, 

 as widely removed as 

 possible. The difference 

 in the latent period of the 

 two curves, which are 



FIG. 161. Rate of transmission of excitation in motor obviously nOll- Coincident, 

 nerve of frog (Pouillet's method). (Helmholtz.) n , 



but otherwise congruent 



{Fig. 162), corresponds to the rapidity with which the excitation 

 is transmitted in the intermediate tract of nerve. In the 

 motor nerves of the frog, at room temperature, this is about 

 27 m. per sec. Experiments on man by the same method 

 (muscles of ball of thumb) give a much higher result (34 m.). 

 Further observations of Chauveau on the nerves of smooth 



Fio. 162. Separation of curves of twitch on exciting the frog's sciatic close to the spinal cord, 

 and 5 mm. from the knee. (Engelinanii.) 



muscles in mammals are interesting, as showing that the rate of 

 conductivity is much lower in these than in the nerves of striated 

 muscle. It hardly reached 8 m. per sec. The rate of conduc- 

 tivity in non-medullated nerves of many invertebrates appears to 

 be still lower, even when they are connected with striated 

 muscles. Fredericq and Vandervelde (15) found, according to 

 the temperature (10-20 C.), 6-12 m. in the claw-nerves of the 



