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[ Pg 81 ] CHAPTER III . ON SOME GENERAL CONDITIONS OF BRAIN - ACTIVITY . The elementary properties of nerve - tissue on which the brain - functions depend are far from being satisfactorily made out . The scheme that suggests itself in the first instance to the mind , because it is so obvious , is certainly false : I mean the notion that each cell stands for an idea or part of an idea , and that the ideas are associated or ' bound into bundles ' ( to use a phrase of Locke's ) by the fibres . If we make a symbolic diagram on a blackboard , of the laws of association between ideas , we are inevitably led to draw circles , or closed figures of some kind , and to connect them by lines . When we hear that the nerve - centres contain cells which send off fibres , we say that Nature has realized our diagram for us , and that the mechanical substratum of thought is plain . In some way , it is true , our diagram must be realized in the brain ; but surely in no such visible and palpable way as we at first suppose . [ 99 ] An enormous number of the cellular bodies in the hemispheres are fibreless . Where fibres are sent off they soon divide into untraceable ramifications ; and nowhere do we see a simple coarse anatomical connection , like a line on the blackboard , between two cells . Too much anatomy has been found to order for theoretic purposes , even by the anatomists ; and the popular - science notions of cells and fibres are almost wholly wide of the truth . Let us therefore relegate the subject of the intimate workings of the brain to [ Pg 82 ] the physiology of the future , save in respect to a few points of which a word must now be said . And first of THE SUMMATION OF STIMULI in the same nerve - tract . This is a property extremely important for the understanding of a great many phenomena of the neural , and consequently of the mental , life ; and it behooves us to gain a clear conception of what it means before we proceed any farther . The law is this , that a stimulus which would be inadequate by itself to excite a nerve - centre to effective discharge may , by acting with one or more other stimuli ( equally ineffectual by themselves alone ) bring the discharge about . The natural way to consider this is as a summation of tensions which at last overcome a resistance . The first of them produce a ' latent excitement ' or a ' heightened irritability ' — the phrase is immaterial so far as practical consequences go ; the last is the straw which breaks the camel's back . Where the neural process is one that has consciousness for its accompaniment , the final explosion would in all cases seem to involve a vivid state of feeling of a more or less substantive kind .
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