TRANSMISSION IN BOTH DIRECTIONS. 457 



stem of the nerve fibre is excited. 1 The only possible interpretation of 

 these phenomena is the transmission of the excitatory state up the 

 efferent nerve fibre to the main stem, and along every one of its branches ; 

 if these lead to a terminal organ which responds to the arrival of the 

 state, such response is evoked. 



A question of some interest does not appear as yet to have been 

 investigated. Is the rate of such propagation the same whether it is 

 opposed to that of the normal functional activity, or is similarly directed 

 to this ? In other words, is there any evidence of irreciprocal con- 

 ductivity ? The writer has attempted to obtain information on this 

 point by utilising the comparatively long single axis cylinder of the 

 electrical nerve of Malapterurus. The difficulties are largely due to the 

 slight differences in time measurement which are involved. As far as 

 the series of experiments throws light upon the subject, it appears that 

 the rate of transmission in the preparations used was not materially 

 affected by the direction of such transmission ; at any rate, it may be 

 safely said that the average rate was the same, whether the propagation 

 ascended or descended this efferent nerve (Fig. 251, C, excitation at x l 

 and x. 2 respectively). 



A further proof of this conductivity in both directions is that 

 afforded by the electrical changes accompanying the development of 

 the excitatory state in the nerve. This, in the case of efferent nerves, 

 is shown by the division of an anterior root of the sciatic plexus in an 

 animal such as the cat, and the connection of the root with an appropriate 

 galvanometer. Excitation of the trunk of the sciatic evokes both a 

 response in the muscles of the limb and electrical changes in the anterior 

 root, due to the propagation of the excitatory state upwards towards 

 the central nervous system. A remarkable feature of this propagation 

 up efferent nerves is its absolute extinction on its arrival at the central 

 nervous system, there being no trace of any excitatory electrical change 

 in the spinal cord. 2 Similar methods may be applied to afferent nerves ; 

 here it is sufficient to expose and excite a posterior root, and determine 

 the existence of excitatory electrical changes in the central end of the 

 cut sciatic. These are produced not only by the stimulation of the 

 posterior root, but by excitation of the spinal cord after all the anterior 

 roots have been cut, due to the circumstance that the posterior root 

 fibres are directly prolonged by branches into the posterior columns of 

 the cord. 



Various expedients were formerly resorted to in order to demonstrate the 

 possibility of reversed propagation along afferent nerves. Among these is 

 that of dividing the hypoglossal and lingual nerves in the dog, and then 

 suturing the peripheral portion of the former and the central portion of the 

 latter. It was thought that the fact of the contraction of the tongue muscles, 

 which could after some weeks be evoked by the excitation of the lingual, 

 showed transmission along the afferent fibres of this nerve, which had become 

 united to the efferent ones of the hypoglossal. Such experiments, and those 

 of Paul Bert, which involved a transplantation of the tail of the rat, by 

 grafting its cut tip in a fresh situation on the skin, are all futile, since 

 they were carried out before the phenomena of nerve degeneration, and nerve 

 regeneration had been adequately appreciated. There is no evidence of such 

 direct union of nerve fibres as that demanded by these experiments, nor, if 



1 Babuchin, Arch.f. PhysioL, Leipzig, 1877, S. 66. 



2 Gotch and Horsley, Phil. Trans., London, 1891, vol. clxxxii. B., p. 485. 



