440 



Messrs. F. Gotch and G. J. Burch. 



excited by a single stimulus. The elimination of all propagation owing 

 to the structure of the tissue, is a factor of great importance in this 

 connection since such complete elimination is, in our opinion, not 

 experimentally possible in the case of either muscle or nerve. Both 

 the quicker rise and the slower fall may therefore be regarded as 

 expressions of the character of the local change in the nerve endings. 



Such a difference between the rate of development and of subsidence 

 of the excitatory explosion was indicated in our earlier experiments, 

 although not referred to in our published paper.* In those experi- 

 ments we find, on examining carefully twelve different records, the fol- 

 lowing relation between the duration of the two states, development 

 and subsidence : — 



Duration of development _ 265 81 

 Duration of subsidence 326' 100 ' 



In the present instance, possibly owing to the more effectual cooling, 

 the more prolonged character of the subsidence is very conspicuous. 

 Thus in the two analysed instances, here referred to, we find 



Duration of development 7 44 8 47 

 -L ~— ■ Qp cinci oi* 



Duration of subsidence 16 ' 100 ' 17 ' 100 ' 



One other point of interest in connection with the development of 

 the E.M.F. is the comparatively gradual character of its actual com- 

 mencement. The analysis shows that for 0*002 second after a 

 potential difference can be detected, its value is relatively small. 



It might be objected that the gradual development and still more 

 gradual subsidence of the E.M.F. may have some purely physical 

 explanation apart from the physiological change in the nerve endings, 

 such, for instance, as polarization capacity due to the special structure 

 of the tissue. That this is not the case is clearly proved by experiments 

 in which a strong induction shock traversed the organ, which failed to 

 excite it but was itself recorded on the plate. "We have several 

 examples of induction shocks of different intensities, of condenser dis- 

 charges, and of excursions due to transient currents through the same 

 circuit. In none of these is there any resemblance to the peculiar form 

 of the curve given by the organ response. We are therefore in a posi- 

 tion to say that the time relations of the organ shock do not resemble 

 those of either induction currents, condenser discharges, or currents of 

 short duration from a source of constant E.M.F. 



(3) The duration of the period between the excitation of the nerve 

 and the commencement of the organ response (0*017 sec.) represents 

 the transmission time of the excitatory state along 40 mm. of nerve 

 fibre when cooled to 5° C, this being the distance between the seat of 



* ' Phil. Trans.,' B, vol. 187 (1896), p. 347. 



