EXCITABILITY AND CONDUCTIVITY IN NERVES. 483 



readily evoked by excitation, either of the nerve trunk or of the 

 whole organ and its contained nerves. But whereas the muscular 

 response is retarded by '003 sec. to '005 sec., with indirect as compared 

 with direct modes of stimulation, no such difference is found in 

 the electrical organ of either Malapterurus or Torpedo, provided the 

 nerve trunk is excited close to its point of entry into the organ. In 

 both cases a minimal delay of '003 sec. to '005 sec. occurs. 1 It would 

 appear, therefore, that the electrical response is not that of another 

 organ apart from the nerves, but is the excitatory change in the nerve- 

 endings. If this is so, then the delay of '003 sec. to '005 sec. must be 

 regarded as due to retarded transmission in the nerve arborisations. 

 It is not improbable that a portion of the so-called excitatory time 

 (003 sec, to 005 sec.) of the motorial nerve-endings of muscle is in 

 reality the time consumed by the slower rate of transmission along 

 these fine nerve twigs, which thus resemble the non-medullated nerves 

 in their retarded rate of propagation. 



As regards the central terminations, we have no means at present of 

 ascertaining how the extra delay is to be apportioned between the fine 

 nerve-endings, the unknown field of conjunction, and the branches 

 of the efferent cell through which it is discharged into the issuing 

 efferent fibres. It is, however, logical to assume that in each one of 

 these three situations the difference of structure involves a correspond- 

 ing difference in the rate of propagation, and that central delay is the 

 sum of the retardation in all these situations. 



The transmission time through the substance of a nerve cell is com- 

 monly assumed to differ from that along a nerve fibre ; but evidence 

 of such difference cannot be said to be at all conclusive. For its 

 ascertainment the preparation must be one in which the cell is 

 bipolar, with processes on both sides of considerable length. Exner 

 estimated the rate of propagation of the electrical nerve response along 

 the sciatic nerve of the frog, through the posterior root ganglion into 

 the posterior root, and found that the interposition of the ganglion 

 did not appreciably affect the time relations of such excitatory electrical 

 changes. 2 In opposition to this result is that of Wundt, 3 who found 

 the reflex response to be delayed when the ganglion formed part of the 

 conducting afferent tract. Excitation on the proximal and distal side 

 of the ganglion stellatum in Eledone moschatus is associated with an 

 alteration in the muscular responses. 4 Finally, Gad showed that the 

 interposition of the vagus ganglion caused a very considerable retarda- 

 tion of from '03 sec. to '04 sec. in the respiratory centre inhibition, which 

 is produced by excitation of the vagus trunk. 5 It is not impossible that 

 the change of the excitatory state in its passage through the ganglion 

 cell may be of a complex kind, and that it may be so altered in 

 character as to be a weaker afferent stimulus on its arrival at the 

 central endings. Such a supposition would of itself account for the 

 extra delay in the central response to impulses which have traversed 

 the ganglion, irrespective of any additional retardation ; hence the 



1 Gotch, Phil. Trans.. London, 1887, B, p. 510 ; Gotch and Burch, ibid., 1896. B, 

 p. 347. 



2 Exner, Arch. f. PhysioL, Leipzig, 1877, S. 567. Confirmed by Moore and Reynolds, 

 "Proc. Phys. Soc.," March 1898, Journ. PhysioL, Cambridge and London. 



3 Wundt, "Untersuch. z. Mechanik der Nerven u. Nerven Centrum," Bd. ii. S. 45. 



4 Uexkiill, Ztschr. f. BioL, Bd. xxx. S. 317. 



5 Gad, Arch.f. PhysioL, Leipzig, 1889, S. 199. 



