530 



NERVE. 



stimulus may be readily calculated. Outlines of such records are shown 

 in Fig. 270, and the results confirm those obtained by means of the 

 repeating rheotome. 1 



FIG. 270. Facsimile curves of the photographed excursions of a capillary electro- 

 meter connected with the frog's sciatic nerve. Excitation, 30 mm. from 

 proximal capillary contact by a single induced current at moment marked x. 

 The short dark horizontal line indicates '01 sec. (I), Uninjured fresh nerve ; 

 (21}, fresh nerve with distal contact on warmed area ; (III), excised nerve 

 kept twenty-four hours in 0'6 per cent. NaCl solution ; (IF), excised nerve 

 with distal contact on a recent cross-section. Gotch and Burch. 



(a) Propagation time. The interval of time between the stimulus and 

 the appearance of the change under the surface contact is strictly pro- 

 portional to the distance between the seat of excitation and this con- 

 tact. Hence, if two seats of excitation are so situated that one is twice 

 as far as the other from the surface contact, the interval in question is 

 in the former case twice as long. In the frog's sciatic the interval is such 

 that at a temperature of 15 C. it is '001 sec. for 30 mm. of nerve. The 

 electrical response is thus transmitted at a rate of 30 metres per second, 

 i.e. the same rate as the excitatory process, when estimated by the 

 indirect muscle response, according to the method devised by Helmholtz. 

 Further, since the time at which the effect appears is strictly pro- 

 portional to the distance of the surface contact from the seat of the 

 excitation, it is obvious that the loss of time must be due to transmission 

 and to this only. In other words, there is no delay except that 

 necessitated by uniform propagation at the above rate ; there is, there- 

 fore, no period of delay or latent time in the electrical response of 

 nerve. 2 The propagation time of the electrical response varies in any 

 given nerve, when subjected to changed conditions of temperature, etc. ; 

 it also varies in different parts of a nerve, in different nerves, and in 

 the nerves of different animals. Thus, in the non-medullated nerves of 

 Eledone moschatus the rate of such propagation has been found, in the 

 winter, to be 1 metre per second ; in the summer Boruttau 3 found a 

 rate of from 3J to 5| metres per second, both in Eledone and in 

 Octopus* 



1 Gotch and Burch, Proc. Roy. Soc. London, 1898, vol. Ixiii. p. 300 ; Gotch and 

 Horsley, ibid., vol. xlv. 



2 Bernstein, " Erregungsvorgang im Nerven- u. Muskelsysteme," 1871. 



3 Fuchs, Sitzungsb. d. Tc. Akad. d. Wissensch., Wien, Bd. ciii. Abth. 3, S. 209. 



4 Boruttau, Arch. f. d. ges. Physio!., Bonn, 1897, Bd. Ixvi. S. 285. 



