Page:Mind (New Series) Volume 15.djvu/258

244 CRITICAL NOTICES: than the neurones themselves, they provide a correspondingly- richer, more adequate structural basis for the explanation of that differentiation and specialisation of manifold conduction-paths which is the essential process in the formation of neural habit. For a neurone commonly forms a link in many separate paths of different function, and if canalisation consists in some change in the general substance of the neurone or in its nucleated part, the repeated use of any one of these paths must result in improvement of all of them, a result hardly compatible with that delicate specia- lisation of function which probably underlies all acquisition and education. Wundt's views on these fundamental points inevitably deter- mine his treatment of all the special psycho-physical problems, rendering it somewhat vague and incoherent, and this must seem the more regrettable to those who accept the neurone-theory be- cause that theory harmonises so well the physiological data with the doctrine of psychical elements, which is the basis of Wundt's psychological expositions. Thus, these views must have tended to, if they do not actually necessitate, Wundt's rejection of the doctrine of specific energies of the sensory cortical elements (the modern form of the doctrine of the specific energies of sensory nerves), and his replacement of it by the doctrine of the original indiiference of function of all nervous elements and the adaptation of their func- tions to the stimuli. That in the sensory cortex of the normal adult brain there are elements of specific functions or specialised and in- variable modes of response to stimulation is indisputable ; but Wundt would have us believe that the specific function of each such cortical element is due only to the fact that its substance is continuous with the nervous substance in one or other of the sense-organs, the setting of which renders it peculiarly liable to be affected by some one kind of physical stimulus, which stimulus, repeatedly inducing in the nervous substance some form of change unlike that induced by any other kind of stimulus, impresses upon that substance throughout its course from sense-organ to brain-cortex a tendency to exhibit this specific kind of process whenever stimulated in any way. Wundt lays great stress upon this doctrine, which obviously is incompatible with the neurone-theory as defined above, and speaks somewhat scornfully of the doctrine of innate specific ener- gies as an improbable and superfluous fiction. Yet I venture to think that his doctrine is quite untenable, and that the objections he raises to the rival theory are ill-founded. He attaches great importance to the fact that a person who has never had the use of one of his senses, or has lost it in the first years of life, never enjoys imagery of that sense. But that an organ should fail or cease to function when deprived of its normal stimuli is a rule of general application in physiology ; and we have more decisive evidence in the opposite sense in the fact that a person born blind may experi- ence colour-sensations as soon as the physical defects of his eyes are removed by operation. Wundt relies, too, upon the evidence