Manchester Memoirs, Vol. xlii. (1898), No. 1^. 15 



know how it is that the chemical change in the perikaryon 

 influences that chemical change at the periphery of the axon 

 which is the basis of the local nutrition of that structure. 

 Nevertheless it seems clear that the perikaryon does work 

 for the good of the whole unit and not for the good of 

 itself alone. This is incidentally shewn in the case of the 

 spinal ganglion of the lower vertebrates. In these the 

 cells of the ganglion are bipolar cells. The incoming axon 

 or axon-like dendrite reaching one pole of the perikaryon 

 spreads out, losing itself among it, and then is gathered 

 up at the opposite pole to issue as a veritable axon. In such 

 a case the afferent fibre passes through the substance of 

 the perikaryon, and we may assume that it passes along 

 definite paths, along strands of axon-like material im- 

 bedded in the perikaryonic laboratory mass. Yet we 

 have no evidence that this perikaryonic mass in any way 

 influences the impulses which sweep through the ganglion 

 on their way from the skin to the spinal cord. The peri- 

 karyonic mass influences the whole stretch of axonic 

 material which forms the axis cylinder of the nerve fibre 

 on this side and that side of the ganglion ; but it has no 

 direct and special local effect on the threads of axonic 

 material which traverse itself between the two poles of the 

 cell. It works not for that part of the unit alone but for 

 the whole unit along its whole length. 



This, then, is one fundamental feature of the neurone, 

 that it is essentially a unit, all the various parts being 

 strikingly integrated into a whole, so that whatever affects 

 a part, affects not the part alone but the whole unit. 



A second fundamental feature of the nervous system, 

 to which I now wish to call your attention, is one which 

 1 may introduce under the term of" the differentiation of 

 units." The whole nervous system is, as we have seen, a 

 linkage of units, the linkage being not by real fusion but 

 by contact, the break of continuity between link and link 



