35° 



NA TURE 



[September 9, 1922 



that of its opposite. Again, the position of the stimu- 

 lated sensual point acts on the mind — hence the light 

 seen or the pain felt is referred to some locus in the 

 mind's space-system. Similarly the reflex machinery 

 directs, for example, the limb it moves towards the 

 particular spot stimulated. Such spots in the two 

 processes, mental and non-mental, correspond. 



Characteristic of the nervous machinery is its arrange- 

 ment in what Hughlings Jackson called " levels," the 

 higher levels standing to the lower not only as drivers 

 but also as restrainers. Hence in disease underaction 

 of one sort is accompanied by overaction of another. 

 Thus in the arm affected by a cerebral stroke, besides 

 loss of willed — that is higher level — power in the finger 

 muscles, there is in other muscles involuntary over- 

 action owing to escape of lower centres from control 

 by the higher which have been destroyed. Similarly 

 with the sensory effects ; of skin sensations some are 

 painful and some not, for example, touch. The seat of 

 the latter is of higher level, cortical ; of the former 

 lower, sub-cortical. When cerebral disease breaks the 

 path between the higher and the underlying level a 

 result is impairment of touch sensation but heightening 

 of pain sensation in the affected part. The sensation 

 of touch, as Dr. Head says, restrains that of pain. 



Thus features of nervous working resemble over and 

 over again mental activities. Is it mere metaphor, then, 

 when we speak of mental attitudes as well as bodily ? 

 Is it mere analogy to liken the warped attitude of the 

 mind in a psychoneurotic sufferer to the warped attitude 

 of the body constrained by an internal potential pain ? 

 Again, some mental events seem spontaneous ; in the 

 nervous system some impulses seem generated auto- 

 matically from within. 



It may be said of all these similarities of time-relation 

 and the rest between the ways of the nervous system 

 and such simpler ways of mind as I here venture on, 

 that they exist because the operations of the mental 

 part of the nervous system communicate with the 

 exterior only through the non-mental part as gateway, 

 and that there the features of the nerve-machinery are 

 impressed on the mind's working. But that suggestion 

 does not take into account the fact that the higher and 

 more complex the mental process, the longer the time- 

 lag, the more incident the fatigue, the more striking the 

 memory character, and so on. 



All this similarity does but render more succinct the 

 old enigma as to the nexus between nerve impulse and 

 mental event. In the proof that the working of the 

 animal mechanism conforms with the first law of 

 thermodynamics is it possible to say that psychical 

 events are evaluated in the balance sheet drawn up ? 

 On the other hand, Mr. Barcroft and his fellow-observers 

 in their recent physiological exploration of life on the 

 Andes at 14,200 ft. noted that their arithmetic as well 

 as their muscles were at a disadvantage ; the low 

 oxygen pressure militated against both. Indeed, we 

 all know that a few minutes without oxygen, or a few 

 more with chloroform, and the psychical and the 

 nervous events will lapse together. The nexus between 

 the two sets of events is strict, but for comprehension of 

 its nature we still require, it seems, comprehension of 

 the unsolved mystery of the " how " of life itself. A 

 shadowy bridge between them may lie perhaps in the 

 reflection that for the observer himself the physical 



NO. 2758, VOL. I IO] 



phenomena he observes are in the last resort 

 psychical. 



The practical man has to accept nervous function as 

 a condition for mental function without concerning 

 himself about ignorance of their connexion. We know 

 that with structural derangement or destruction of 

 certain parts of the brain goes mental derangement or 

 defect, while derangement or destruction of other parts 

 of the nervous system is not so accompanied. Decade 

 by decade the connexion between certain mental per- 

 formances and certain cerebral regions becomes more 

 definite. Certain impairments of ideation as shown by 

 forms of incomprehension of language or of familiar 

 objects can help to diagnose for the surgeon that part 

 of the brain which is being compressed by a tumour, 

 and the tumour gone the mental disabilities pass. 

 Similarly those who, like Prof. Elliot Smith and Sir 

 Arthur Keith, recast the shape of the cerebrum from 

 the cranial remains of prehistoric man, can outline for 

 us something of his mentality from examination of the 

 relative development of the several brain regions, using 

 a true and scientific phrenology. 



Could we look quite naively at the question of a seat 

 for the mind within the body we might perhaps suppose 

 it diffused there, not localised in any one particular part 

 at all. That it is localised and that its localisation is in 

 the nervous system — can we attach meaning to that 

 fact ? The nervous system is that bodily system the 

 special office of which, from its earliest appearance 

 onward throughout evolutionary history, has been more 

 and more to weld together the body's component parts 

 into one consolidated mechanism reacting as a unity to 

 the changeful world about it. More than any other 

 system it has constructed out of a collection of organs 

 an individual of unified act and experience. It repre- 

 sents the acme of accomplishment of the integration of 

 the animal organism. That it is in this system that 

 mind, as we know it, has had its beginning, and with 

 the progressive development of the system has developed 

 step for step, is surely significant. So it is that the 

 portion in this system to which mind transcendently 

 attaches is exactly that where are carried to their 

 highest pitch the nerve-actions which manage the indi- 

 vidual as a whole, especially in his reactions to the 

 external world. There, in the brain, the integrating 

 nervous centres are themselves further compounded, 

 inter-connected, and re-combined for unitary functions. 

 The cortex of the forebrain is the main seat of mind. 

 That cortex with its twin halves corresponding to the 

 two side-halves of the body is really a single organ 

 knitting those halves together by a still further knitting 

 together of the nervous system itself. The animal's 

 greal integrating system is there still further integrated 

 and this supreme integrator is the seat of all that is 

 most clearly inferable as the animal's mind. As such 

 it has spelt biological success to its possessors. From 

 small beginnings it has become steadily a larger and 

 larger feature of the nervous system, until in adult man 

 the whole remaining portion of the system is relatively 

 dwarfed byit. Itis not without significance, perhaps, that 

 in man this organ, the brain cortex, bifid as it is, shows 

 unmistakable asymmetry. Man is a tool-using animal, 

 and tools demand asymmetrical, though attentive and 

 therefore unified, acts. A nervous focus unifying such 

 motor function will, in regard to a laterally bipartite 



