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Cavendish Lecture[ABSTRACT]

ON

VISION AND EVOLUTION.

Delivered on May 28th before the West LondonMedico-Chirurgical Society

BY G. ELLIOT SMITH, M.D., F.R.C.P., F.R.S.,PROFESSOR OF ANATOMY IN THE UNIVERSITY OF LONDON.

IN the vast majority of living animals behaviour isdominated either by smell or vision. Of these smellis the more primitive and fundamental factor. Thecerebral cortex was evolved from that part of thebrain which originally was little more than thereceptive centre for impressions of smell and theinstrument for enabling the sense of smell to influencethe animal’s behaviour. Unlike all the other sensory Itracts, those which convey impulses from the olfactory Iorgan reach the cerebral cortex directly-that is,without passing through the thalamus. From apsychological point of view, therefore, the sense ofsmell occupies a unique and distinctive position. Itrepresents the germ of all the higher psychical powers,or, perhaps it would be more accurate to say, thecement that binds together the elements out of whichthe powers of the cerebral cortex, as the repository ofthe impressions of past experiences, the organ ofdiscrimination and appreciation of space and time,are developed.

RIVALRY BETWEEN SMELL AND VISION.In the primitive vertebrate behaviour is dominated

by the sense of smell. It is the means by which theanimal finds its food and determines its qualities, bywhich it recognises friends or enemies, sexual mates, orrivals. Smell is possessed of affective qualities whichendow it with a direct meaning such as is not associatedwith either of the other two " distance receptors "(Sherrington), vision and the eighth nerve sense. Inthe primitive vertebrate living in the water smell ismuch more nearly akin to taste than it is in man andthe land-living animals. When such’ an animalperceives the odour of food it is really getting a fore-taste of the consummation of the reaction, when itcaptures the food and actually tastes it. Throughoutthe whole of the anticipatory phase it is under theinfluence of olfactory sensations. A series of events,covering the whole period of anticipation and con-summation, is linked together by the affective tone ofsmell into one experience, which includes the germ ofmemory and of spatial and temporal appreciation.Thus it confers upon experience the element ofcoherence. But the sense of smell itself conveys onlythe vaguest indications of spatial relations. Ananimal attracted by a scent circles around it until itcomes within visual range of its quarry ; then theeyes convey more precise information as to itsposition in space and as to its movements. Suchvisual information is almost entirely devoid ofaffective tone, of psychological meaning, which itacquires secondarily from the sense of smell. But it isbiologically useful, because it enables the creature tosteer its course more directly and accurately to theobject of the pursuit ; and for this reason it is theoptic receptive centre, the tectum of the mid-brain,which in the primitive vertebrate is put into directconnexion with the motor nuclei and directs themovements of the animal. The sense of smell startsthe reaction, the sense of sight directs it.

In the course of the pursuit of its prey, when theanimal is impelled by the sense of smell and controlledby its dominating affective tone, the informationcollected by all the other sensory mechanisms is addedto and woven into the tissue of the complex experience.Hence these other senses acquire a meaning and ashare in the psychical activities which constantlyncreases in importance throughout the vertebrate

series, until it culminates in the vast mental powers ofman, in which smell plays a humbler and less obtrusivepart, although still one of imperious importance,especially in matters that concern the appetites andsentiments.

In the whole history of living animals, both inver-tebrate and vertebrate, there has been a constantrivalry between smell and vision for dominance.Behaviour in the primitive members of every group iscontrolled pre-eminently by smell, and invariably inthe more efficient members of such groups vision hasusurped the control-as in the teleostean fishes, inbirds, and the highest mammals. But in all vertebrateclasses excepting mammals visual dominance is.attained only at the expense of a precocious specialisa-tion that is fatal to progress-or, at any rate, to thekind of advancement that leads towards the attain-ment of the human type of intelligence. In the brainof the primitive vertebrate the cerebral hemisphere isessentially the receptive instrument for olfactoryimpulses, whereas visual impulses are received mainlyby the midbrain. Hence a precocious increase of theinfluence of vision involves a development of themidbrain at the expense of the forebrain, and in thatsense is fatal to the evolution of the brain in thedirection of the enhancement of the functions of thecerebral cortex.

REPRESENTATION OF VISION IN THE CORTEX.It is only in mammals in which vision, so to speak,

has secured representation in the cerebral cortexthat fuller reliance on vision does not involve animpairment of the influence of the cerebral cortex.In mammals, in fact, the cultivation of vision acts asthe most powerful stimulus to the growth and elabora-tion of the cerebral cortex and the progressivedevelopment of its psychological possibilities.While no normal human being can possibly fail to

appreciate in a general way how great a boon visionis I do not think that any adequate appreciation hasyet been made of the vast significance of the visualfactor in evolution. To us the world and most of whatis happening in it is made known to us by sight. Theattainment of muscular skill is determined mainly bythe correlation of eye and hand, the eyes guiding thehand in acquiring what we significantly call dexterity.Our appreciation of beauty is based essentially on thevisual appreciation of form, proportion, colour, andtexture, as well as of movement.No one can question the tremendous influence of

these aesthetic qualities on human relations or doubtthe reality of sexual selection in mankind. But inaddition to the part such factors play in determiningaesthetic feeling and sexual choice vision is possiblythe most significant means of intercommunicationbetween human beings. We judge our fellow men andwomen by their movements, their gestures andexpressions. We read their feelings and intentions intheir facial movements and feel that these speak atruer language than the words of articulate speech.In particular the eyes themselves are the most eloquentsignals of the sentiments and emotions, a fact thatfinds ample expression not merely in the commonexperience of every human being, but also in ourcommon speech and poetry, and in particular theslang phrases of every language. In addition the eyesafford indications not merely of the emotions but alsoof men’s thoughts and intentions. Watching anotherhuman being one almost instinctively appreciates thedirection of their visual axes and from such o1::serva-tions interprets the subject upon which attention isfixed. Speech was primarily the expression by acousticsymbols of the intercommunication of the thoughts ofhuman beings, which previously had been expressedmore truthfully but with less precision by signals ofthe eyes and facial muscles and manual gestures thatappealed to vision.

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Vision was, moreover, the fundamental factor in thedevelopment of intelligence of the human type. It isthe essential instrument for observation a.nd the processof learning by experience and especially by thattraining of hand and eye we call experimentation..

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The vocabulary of every language provides eloquentexpression to the fundamental influence of vision inour intellectual life. Its symbolism is predominantlyvisual-insight, foresight, and the rest. In man’sancestors the increasing reliance upon visual guidanceby mammals with plastic undifferentiated-i.e.,adaptable hands, made possible the emergence ofthose progressively expanding powers of discrimina-tion that eventually led to the emergence of thedistinctive powers of intelligence. The eyes guidedthe hands to learn an increasing number of acts ofskill. This incidentally cultivated the power of tactilediscrimination and correlation between touch andvision. The increasing powers of regulating complexmovements eventually conferred upon the cerebralcortex the ability to extend the range and precisionof the conjugate movements of the eyes. This createdthe conditions that are essential before a true maculalutea can develop in a mammalian eye. In addition,it made possible the attainment of stereoscopicpowers. I need not repeat that argument again,but I refer to it to call attention to newly realisedfactors that play a part in the process.

ITS PART IN POSTURE AND BEHAVIOUR.The researches of Sir Charles Sherrington and his

collaborators, especially Prof. Magnus, of Utrecht,have been responsible for calling attention to otherways in which the eyes come to play a part in thecontrol of posture and behaviour. With the increasingreliance of vision the eyes acquire an influence inthe regulation of posture (and the automatically-controlled muscular tone that is an essential part ofthe maintenance of posture) that is lacking in othermammals. The other posture-regulating mechanisms- labyrinthine, cervical, and cutaneous-are con-

trolled by the brain-stem. The ocular regulation ofposture, though automatic, involves the cerebralcortex. It thus becomes more intimately associatedwith the function of acquiring muscular skill. Theeventual attainment of the erect attitude by man isone of the expressions of this enhancement of theinfluence of vision and the increased part it plays inthe regulation of posture and muscular activity ingeneral.

SOME REMARKS ON OSTEOMALACIA,WITH SPECIAL REFERENCE TO A

RECENT CASE.

BY F. S. FOWWEATHER, M.D. LIVERP., M.Sc.,F.I.C., D.P.H.,

LECTURER IN CHEMICAL PATHOLOGY UNIVERSITY OF LEEDS ;CHEMICAL PATHOLOGIST, LEEDS GENERAL INFIRMARY.

THE case about to be described was admitted to theLeeds General Infirmary in September, 1925. Asomewhat full chemical investigation was made andthe results obtained appear to be of sufficient interestand importance to be worthy of record.The patient was a tailoress aged 27. On admission the

limbs were thin and wasted, the abdomen very protuberant,and there was marked scoliosis. The most remarkablefeature, however, was the extreme distortion of the sternum,which projected forward at an acute angle. These featuresare illustrated in the accompanying photograph. In additionthe terminal phalanx of the right thumb was bent backwards.

She was quite well until 1919, when she complained ofbackache and some difficulty in walking. She was advisedto rest in bed for three months, and at the end of this periodshe found that she was shorter in height and had lost weight.Difficulty in walking persisted for 12 months. A holiday oftwo months’ duration was followed by considerable improve-ment, and she resumed work for nine months, but had todiscontinue owing to " rheumatism." This occurred inwinter, and she has been unable to work in winter eversince. During the past year she has had two attacks ofbronchitis, each of about three weeks’ duration. For sometime before admission she had had attacks of fainting withmarked dyspncea. These attacks came on at irregularintervals and, in view of the subsequent findings, wereprobably manifestations of acidosis. There was no associa-

tion of pregnancy with the condition, the patient beingunmarried and a virgin.The X ray report by Mr. H. B. Scargill was as

follows :-" The pelvis shows marked flattening and rarefaction of

bone ; the neck of each femur has lost its angle (now almosta right angle). Terminal phalanx of right thumb showsdeformity. Chest : Nothing reliable can be made out.I do not think there is any doubt about the diagnosis ofosteomalacia. "

I The chemical findings in this case are of considerableinterest. They are as follows :-

Acetone was present, but was not estimated.

Starvation Acidosis.The outstanding features of these results are the

low CO2-combining power of the blood together witha lowered sodium and chloride value, with an increasedammonia coefficient and acetone in the urine. Thereis, therefore, a moderate degree of acidosis. Otherinteresting features are :-

1. The blood calcium is normal, while the urine calciumapproaches the upper limit of normal calcium urinaryexcretion. Balance experiments by Freund and Lockwood 1have shown that a definite loss of calcium from the body