PRESIDENTIAL ADDRESS. 715 



of reflex movements is such as to indicate the rhythmical discharge of groups of 

 centrifugal nerve impulses whose periodicity bears no relation to that of the 

 centripetal ones. But it must be remembered that even in nerve fibres it is 

 possible tor a succession of stimuli to evoke a diti'erent succession of electrolytic 

 changes and of nerve impulses, provided that some of the successive stimuli fall 

 within the period of inexcitability which occurs during the establishment of each 

 new electrolytic poise.' We have, therefore, only to assume, as is very probable, 

 that in the central portion of the nervous path this poise is prolonged in its 

 development, and numbers of centripetal impulses must necessarily fail ; hence 

 the emergent ones will have a special periodicity indicative of the duration of 

 the swing of the electrolytic rearrangement which occurs when the synapses jsZms 

 the cells are traversed by the entering impulse. 



The second feature which more particularly suggests spontaneous cellular 

 activity is the well-known fact that reflex centrifugal discharges may continue 

 after the obvious centripetal ones have ceased. This is pre-eminently the case 

 when the central mass is rendered extremely unstable by certain chemical com- 

 pounds, such as strychnine, &c, There are, however, suggestive iodications in 

 connection with such persistent discharges. The more completely all the centri- 

 petal paths are blocked by severance and other means, the less perceptible is such 

 persistent discharge, and since nervous impulses are continually streaming into the 

 central mass from all parts, even from those in apparent repose, it would seem that 

 could we completely isolate nerve cells, their discharge would probably altogether 

 cease. In this connection a suggestive experiment was carried out some years 

 ago upon the spinal cord of the mammal.^ A portion was isolated in situ by 

 two cross-sections, and a part of this isolated cord was split longitudinally into 

 a ventral half containing the motor or centrifugal nerve cells and a dorsal half 

 containing the breaking up of the centripetal nerves; each half was then examined 

 for those electrolytic changes which indicate the presence of nervous impulses. 

 It was found that, even in the strychnised animal, no electrical efl"ect3 could be 

 detected in the ventral half of the cord or its issuing roots, although such eflects 

 were marked in the whole cord, and occurred in the dorsal half which contained 

 the centripetal nerve fibres. 



This experiment indicates that even in the hyper-excitable condition produced 

 by strychnine the spinal motor nerve cells did not discharge centrifugal impulses 

 when cut off from their centripetal connections. It is corroborated by the results 

 obtained by Baglioni in the frog and small mammal,' and, taken in connection 

 with those previously mentioned, it affords considerable foundation for asserting 

 that the chief role of the nerve cell is trophic, and that, as regards issuing nerve 

 impulses, it only forms a modified part of the conducting path. The more we 

 investigate the physiology of the nervous system, the stronger becomes our belief 

 that for centrifugal discharges to occur centripetal impulses must be primarily 

 started either in the peripheral sensory surfaces by changes of a physical or chemical 

 type occurring in the external world, or at some point in the nerve continuum by 

 local chemical or physical changes within the body, especially those due to the 

 chemical condition of the blood. Having been thus started they course along 

 definite structural paths, and the only direct indications of this passage consist 

 of such phenomena as would be produced by the redistribution of concentrated 

 groups of electrolytes — a purely physico-chemical process. 



This coDception places the propagation of the nervous excitatory state as 

 the sole determining factor of nerve activities, central or peripheral. It derives 

 additional support from the circumstance that it is in harmony with that 

 aspect of these activities which is comprised under the term, inhibition. Any 

 efi'ective regulating system must be able to bring into play both incentive and 



' Gotch and Burch, Journ. of Physiol., vol. xxiv. 1899, p. 410 ; Boycott, Joiirn. 



of Physiol., vol. xxiv. 1899, p. 144 ; Buchanan, Journ. of Physiol., vol. xxvii. 1901, 



p. 88, &c. 



" Gotch and Horsley, Phil. Tram., vol. clxxxii. pp. 267-626. (London, 1891.) 

 ' Baglioni, Archivf. die Ges. Physiol., 1900, Supplement, pp. 198-242. (Leipzig.) 



