MEMORY 523 



driteHL'ontact, while Amnesia or the phenomenon of forgetting repre- 

 sents the breaking of a contact previously established. To this view 

 there attach most of the difficulties attendant upon Munk's hypothesis 

 and, furthermore, as Meyer has very justly pointed out 1 the invo- 

 cation of such hypothetical structural changes to explain the physical 

 correlates of psychic phenomena must necessarily lead, sooner or later, 

 to the invention of a metaphysical entity to keep the apparatus in 

 order. Meyer expresses this difficulty as follows : " Why does the pro- 

 toplasm stretch toward one neighboring neurone when the organism 

 happens to be in one situation, toward another neurone when the organ- 

 ism is in another situation? General silence with the neurologists. 

 But some psychologists had an answer ready. They brought in their 

 deus ex machina. The Ghost does it. Consciousness, feeling, will, 

 or whatever you call it, turns the bridge in the proper direction as the 

 switchman turns the switch in a railway-yard." The cytological basis 

 of this hypothesis has also been called severely in question since the 

 investigations of Epathy, Bethe and others have demonstrated the 

 existence of fine intercommunicating fibrils which, in many instances 

 at least, establish anatomical continuity between adjacent dendrites. 



The dynamic conception of the memory-trace, on the other hand, 

 regards it as being formed by a chemical alteration of cell-material 

 along the nervous path which was followed by the stimulus which is 

 subsequently recalled. The superior generality and simplicity of this 

 hypothesis is evident at once. It does not exclude the possible forma- 

 tion of a definite structure as the result of chemical change, on the 

 other hand the persistence of memory traces is at once accounted for 

 since, as we have abundant reason to know, chemical changes within 

 living organisms may be as enduring as life itself. 



We have seen (Chapter XVIII) that the rate of conduction of 

 impulses in Nerve-fibers is conditioned partly if not wholly by physical 

 changes which underlie the passage of the impulse. We infer this from 

 the low Temperature-coefficient of conduction in peripheral nerve- 

 fibers. In Nerve-cells, on the contrary, the passage of impulses is 

 demons trably accompanied by chemical changes. The temperature- 

 coefficient for the conduction of impulses in the nerve-cells of the 

 respiratory center and the cardiac ganglion, for example, is of the 

 chemical order of magnitude. Furthermore, as Mosso has demon- 

 strated, excitation of the cerebral cortex results in a pronounced 

 disengagement of heat. Repeated attempts to demonstrate a similar 

 evolution of heat in nerve-fibers in consequence of stimulation have 

 failed. The processes which attend the conduction of impulses through 

 nerve-cells, therefore, appear to be of a fundamentally different char- 

 acter from those which accompany the passage of impulses in nerve- 

 fibers. 



The effect of the chemical change which accompanies the passage of 



1 Meyer: Journal of Philos. Psychol. and Scientific Methods, 1912, 9, p. 365. 



