September 9, 1922] 



NA TURE 



349 



eye long before the two eyelids have been separated, let 

 alone ere hurt or even light can reach it ; of the butter- 

 fly's wing within the chrysalis for future flight. The 

 nervous system in its repair, as in its original growth, 

 shows us a mechanism winking through phases of non- 

 functioning preparation in order to forestall and meet 

 a future function. It is a mechanism against the 

 seeming prescience of which is to be set its fallibility 

 and its limitations. The " how " of its working is at 

 present chiefly traceable to us in the steps of its results 

 rather than in comprehension of its intimate reactions ; 

 as to its mechanism, perhaps the point of chief import 

 for us here is that those who are closest students of it 

 still regard it as a mechanism. If " to know " be " to 

 km iw the causes " we must confess to want of knowledge 

 of how its mechanism is contrived. 



If w r e knew the whole " how " of the production of 

 the body from egg to adult, and if we admit that every 

 item of its organic machinery runs on physical and 

 chemical rules as completely as do inorganic systems, 

 will the living animal present no other problematical 

 aspect ? The dog, our household friend — do we exhaust 

 its aspects if in assessing its sum-total we omit its mind ? 

 A merely reflex pet would give little pleasure even to 

 the fondest of us. True, our acquaintance with other 

 mind than our own can only be by inference. We may 

 even hold that mind as an object of study does not come 

 under the rubric of Natural Science at all. But this 

 Association has its Section of Psychology, and my 

 theme of to-night was chosen partly at the suggestion 

 of a late member of it. Dr. Rivers, the loss of whom we 

 all deplore. As a biologist he viewed mind as a bio- 

 logical factor. Keeping mind and body apart for 

 certain analytic purposes must not allow us to forget 

 their being set together when we assess as a whole even 

 a single animal life. 



Taking as manifestations of mind those ordinarily 

 received as such, mind does not seem to attach to life, 

 however complex, where there is no nervous system, nor 

 even where that system, though present, is little 

 developed. Mind becomes more recognisable the more 

 the nerve-system is developed ; hence the difficulty of 

 the twilit emergence of mind from no mind, which is 

 repeated even in the individual life history. In the 

 nervous system there is what is termed localisation of 

 function — relegation of different works to the system's 

 different parts. This localisation shows mentality, in 

 the usual acceptation of that term, not distributed 

 broadcast throughout the nervous system, but restricted 

 to certain portions of it ; for example, among verte- 

 brates to what is called the forebrain, and in higher 

 vertebrates to the relatively newer parts of that fore- 

 brain. Its chief, perhaps its sole, seat is a comparatively 

 modern nervous structure superposed on the non-mental 

 and more ancient other nervous parts. The so-to-say 

 mental portion of the system is placed so that its 

 commerce with the body and the external world occurs 

 only through the archaic non-mental remainder of the 

 system. Simple nerve impulses, their summations and 

 interferences, seem the one uniform office of the nerve- 

 system in its non-mental aspect. To pass from a nerve 

 impulse to a psychical event, a sense-impression, percept, 

 or emotion is, as it were, to step from one world to 

 another and incommensurable one. We might expect, 

 then, that at the places of transition from its non-mental 



NO. 2758, VOL. I IO] 



to its mental regions the brain would exhibit some 

 striking change of structure. But it is not so ; in the 

 mental parts of the brain there is nothing but the same 

 old structural elements, set end to end, suggesting the 

 one function of the transmission and collision of nerve 

 impulses. The structural inter-connexions are richer, 

 but that is merely a quantitative change. 



I do not want, and do not need, to stress our inability 

 at present to deal with mental actions in terms of 

 nervous actions, or vice versa. Facing the relation 

 I mi 1 11 ■ in upon us as existent between them, however, 

 may we not gain some further appreciation of it by 

 reminding ourselves even briefly of certain points of 

 contact between the two ? Familiar as such points are, 

 I will mention rather than dwell upon them. 



One is the so-called expression of the emotions. The 

 mental reaction of an emotion is accompanied by a 

 nervous discharge which is more or less characteristic 

 for each several type of emotion, so that the emotion 

 can be read from its bodily expression. This nervous 

 discharge is involuntary, and can affect organs, such as 

 the heart, which the will cannot reach. Then there is 

 the circumstance that the peculiar ways and tricks of 

 the nervous machinery as revealed to us in the study 

 of mere reflex reactions repeat themselves obviously in 

 the working of the machinery to which mental actions 

 are adjunct. The phenomenon of fatigue is common to 

 both, and imposes similar disabilities on both. Nervous 

 exhaustion and mental exhaustion mingle. Then, as 

 offset against this disability, there exists in both the 

 amenability to habit formation, mere repetition within 

 limits rendering a reaction easier and readier. Then, 

 and akin to this, is the oft-remarked trend in both for a 

 reaction to leave behind itself a trace, an engram, a 

 memory, the reflex engram, and the mental memory. 



How should inertia and momentum affect non- 

 material reactions ? Quick though nervous reactions 

 are, there is always easily observed delay between 

 delivery of stimulus and appearance of the nervous end 

 effect ;' and there is always the character that a reaction 

 once set in motion does not cease very promptly. Just 

 the same order of lag and overrun, of want of dead-beat 

 character, is met in sense-reactions. The sensation 

 outlives the light which evoked it, and the stronger the 

 reaction the longer the sensation persists. Similarly 

 the reflex after-discharge persists after the stimulus is 

 withdrawn and subsides more slowly the stronger the 

 reaction. The times in both are of the same order. 

 Again, a reflex act which contracts one muscle commonly 

 relaxes another. Even so, with rise of sensation in one 

 part of the visual field commonly occurs lapse of sensa- 

 tion in another. The stoppage is in both by inhibition, 

 that is to sav, active. Then again, two lights of opposite 

 colour falling simultaneously and correspondingly 

 on the two retinae will, according to their balance, 

 fuse to an intermediate tint or see-saw back and 

 forth between the one tint and the other. Similarly 

 a muscle impelled by two reflexes, one tending to 

 contract it, the other to relax it, will, according to 

 the balance of the reflexes, respond steadily with an 

 intensity which is a compromise between the two, or 

 see-saw' rhythmically from extreme to extreme of the 

 two opposite influences. 



Reflex acts commonly predispose to their opposites ; 

 thus the visual impression of one colour predisposes to 



