THE EVOLUTION OF VISION

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1950-55, only 8 have required operation. These

preliminary results are encouraging; but during therapythere is need for the most careful evaluation of visual

tests, for which the neurosurgeon should be respon-sible. 8 Patients with pituitary adenomas who are

correctly treated can survive a long time.1 These casesare well worth the thoughtful care which must be

given to their diagnosis and management.

Annotations

THE EVOLUTION OF VISION

WHEN Lister returned from Scotland, surgical Londonflocked to his first lecture to hear the latest news of histechnique; but he had been interested in the curdlingof milk, and told the audience, instead, about the Bacilluslactis that he had discovered. Introducing his Listeroration on March 28 with this story, Sir Stewart Duke-Elder elected to talk, not of any detail of eye surgery,but of the Emergence of Vision in the Animal World.He pointed out that whereas most lower animals dependlargely on other senses, and their brains (" nose-brains ")are largely devoted to smell, the human brain is an " eye-brain ", with its receptive area behind, large associationareas, and centres for control and coordination furtherforward.

Sensitivity to light is first manifest as a motor reaction.An amoeba will move away from light as it will from anyother noxious stimulus; some insects move not directlytowards or away from a light but in a direction at a

constant angle to it. By this means an ant, moving ata constant angle to the sun’s rays, can find its way backto its home; but if it is imprisoned in the dark while thesun moves through an arc, when released it will set offin the wrong direction. Moreover, if the source of lightis, unlike the sun, near by, moving at a constant anglewill involve moving in a spiral; that is why the mothflies to its death in a candle flame. Bees can orient them-selves by the sun, but can make a correction for the timeof day, and so can birds. Manx shearwater released inAmerica flew, lost, in any direction on an overcast day,on a sunny day they oriented themselves correctly in40 seconds, and flew across the Atlantic, each to its ownparticular burrow off the west coast of England.These reactions are unlikely to involve visual per-

ceptions. Plants too can react to light-Hedysarum giransnods to a passing cloud-and machines can follow a

torch. In animals purposeful appreciation can reversethe automatism of a response: thus a cockroach, whichnormally avoids light, can be taught to approach it ifthere is a dark shelter underneath. The first animal toshow such intelligent appreciation is the earthworm,which has many light-sensitive cells, and normallyapproaches a dim light and avoids a bright one; butit can be conditioned to respond in other ways. Thusvision for the first time is associated with awareness:the animal can see, though it cannot form an image ofanything. Appreciation of movement in the outside worldis evident in the molluscs: any movement causes theprotrusion of the organs of chemical and tactile sense.

But sensitivity to movement is important in an animalas high as the rabbit, which will run into a stationaryman. Form vision appears in cephalopods-an octopus

8. Ray, B. S. ibid. p. 5.

can distinguish between vertical and horizontal lines-and colour vision in certain insects, though it is importantonly in fishes, birds, and primates.Development of vision depends on environment.

In deep-sea fishes, which live in darkness, it is lost;in small mammals, such as the dog and cat, living nearthe ground, it is less important than tactile and olfactorysensation. The highest development has come in certainfishes (living in a three-dimensional world) and moreparticularly in birds and arboreal creatures-tree-

snakes, tree-shrews, and primates. The swaying habitatof branches necessitated the development of prehensilelimbs and fine stereoscopic vision; moreover, "the securityof the tree-tops allowed an escape from the urgent fearsof life on the ground with its teeming population ofpredators, so that the senses, not constantly alert for

danger, turned to other things ". New explorations byhand and eye gave rise to new associations, curiosity,and inventiveness-the foundation for the intellectual

supremacy of man.A chimpanzee, unlike lower mammals, will amuse

himself visually-by looking at the world upside downor through a hole, or even with a kaleidoscope. This isthe first indication, says Sir Stewart, " that vision hasbecome elevated from the level of biological usefulness toapproach that of aestheticism ". In evolution, he says,there are stages when something new appears differentfrom its constituent parts; thus the molecule differs fromits atoms, and other stages are marked by the emergence oflife and of consciousness. In the evolution of vision thefirst stage is that of the motor reaction, the second thatof perceptual vision, which emerges in the earthwormwith a brain-ganglion, for it needs central nervous

organisation. The third emergent is imaginative vision,exploratory and creative, dependent on the developmentof forebrain and association areas.We know that animals see, but not what they see.

Analysis of our own perceptions is hard; analysis ofthose of dumb creatures is impossible. Sensations canbe appreciated and interpreted only through our per-ceptions ; we know of no corresponding higher stage forthe interpretation of our perceptions. But the brain of a

bee, which can correct for changes in the sun’s positionwith time, is only 1/10 in. across; the brain of man is

vastly bigger, and may expand further. New capacitiesand understandings may well emerge-given time, for theapes threw sticks and stones, and we throw atom bombs.

NOMENCLATURE OF PATHOGENIC FUNGI

THE former unsatisfactory state of the nomenclature offungi pathogenic to man was due, in some measure, toinadequate description of newly named species, whichled to the same species being renamed from time to timeby different authors; also to the tendency to variationinherent in many fungi, the unidentified variant oftenbeing accorded specific rank. These faults gave rise to

multiplication of names, and in a work on pathogenicfungi published twenty years ago some 746

"

species "

were recorded. Since then a new and more scientificinterest in fungus diseases, particularly the systemicinfections, has been aroused by the discovery of theirwidespread distribution in some countries, mainly throughmass radiography of the chest and routine testing for

specific cutaneous sensitivity to fungus antigens.Through the work of the Committee on Medical and

Veterinary Mycopathology of the International Associa-tion of Microbiologists, international agreement on the