714 TRANSACTIONS OF SECTION 1. 



the so-called summation phenomena — that is, the ease with which a succession of 

 centripetal impulses can force a passage as opposed to the difficulty with which a 

 single such impulse does so — is not peculiar to the central mass, but is observed 

 more or less in peripheral nerve endmgs ; for instance, those of electrical organs. 

 Finally, the results obtained by Wedenski suggest that anaesthetics have a par- 

 ticular affinity for nerve endings, including the peripheral ones in the muscles ; 

 and although the causation is at present imperfectly known, it does not seem 

 improbable that they may act upon some such specific substance as that which is 

 conceived of by Langley under the term * receptive.' ^ 



AH the phenomena hitherto described are thus not necessarily aspects of the 

 activity of that particular mass which constitutes the body of the nerve cell, but 

 of nerve endings with their fine arborisations. As regards direct electrical 

 evidence of electrolytic changes in these finer branches, it so happens that Nature 

 has provided some nerve endings on such a magnificent scale that this evidence is 

 readily obtained. In the electrical organs of fishes the essential structure con- 

 sists of a pile of numerous discs each invaded by nerve endings, and the electric 

 shock of the fish is the sum of all the electrical changes in this pile when an 

 eflerent nervous impulse reaches each of its component discs. Its potency is due 

 to the number of these components, but in each single component it is of the same 

 order as the electromotive change in a nerve, and its character is such as might be 

 produced by electrolytic redistribution occurring simultaneously in the immense 

 number of nerve endings which are present in each disc of the electrical organ. 

 Although displaying the peculiarities of apparent delay, &c., just referred to, the 

 general character of the shock of the organ is such as to warrant the belief that 

 electrolytic conceptions of nerve-fibre activity can be extended to the activities of 

 nerve endings. 



There remains that special part of the whole neuron which is the effective 

 source both of its development and of its maintenance, the nerve cell. Continuity 

 with a nerve cell is essential for the integrity of both the structure and the 

 function of a nerve fibre, but it is undoubted that, in its turn, the nerve cell is 

 also dependent upon the existence of its processes in an unimpaired state. Thus 

 the cell sufiers a change which comes on slowly but with great certainty if any 

 part of the neuron has been mutilated, or if the cell has been shorn of some of its 

 offshoots. That it forms a special part of the conducting path is indicated by the 

 occurrence of intracellular and nuclear alterations when a prolonged series of 

 impulses travel towards it, and a further more remarkable point is that it also 

 appears to change if the entering nervous impulses with their electrolytic con- 

 comitants are no longer able to reach it. This suggests that nerve cells, far from 

 being spontaneous actors, are in a very real sense dependents ; they form only 

 one possible conducting portion of the whole differentiated tract, and atrophy when 

 this tract is broken or is from any circumstance not utilised. That the cell is 

 primarily trophic and only incidentally a conductor is suggested by Bethe's 

 experiments upon Crustacea. Owing to pericellular connections the actual nerve 

 cell may be removed in these animals without severing the whole conducting 

 tract, for a portion lies around but outside the cell ; and since, even after such 

 removal, the usual reflex movements of the supplied antennae are resumed, the 

 cell cannot in this instance be regarded as essential for the dischai^e of the 

 motor impulses which evoke the antennae movements.^ 



In higher animals such removal of the cell body has been imperfectly carried out 

 by Steinach in the dorsal spinal ganglia but in the central mass it is impossible 

 to perform a crucial experiment of this kind so as to determine whether or no 

 the substance of nerve cells can create nervous impulses. There are two par- 

 ticular features of reflex movements which may be cited as indicating that a 

 motor nerve cell has at its call a store of nervous energy which it can sponta- 

 neously discharge. The first of these is the well-known fact that the character 



* Wedenski, 'Erregung, Hemmung und Narkose,' Archlvf. die Ges. Physiol, c, 

 1903. 



■< Bethe, AlU/cmeine Anat. u. Physiol, des Ntrvcnsystemt, 1903, p. 99. 



