In many cases we are completely unaware of the response we may make to a stimulus. Strong light causes the iris to expand and reduce the size of the pupil. The taste of food will cause the salivary glands to secrete fluid into the mouth, and the cells of the stomach lining to secrete fluid into the stomach. Temperature changes will bring about alterations in the diameter of certain capillaries. We are more a mass of reflexes than we ordinarily realize.

INSTINCTS   AND   IMPRINTING

The various reflexes I have been talking about are, like the tropisms of plants and the taxis of simple animals, examples of innate behavior — behavior that is inborn and does not have to be learned. You do not have to learn to withdraw your hand from a hot object, or to sneeze if your nasal passages are irritated, or to blink if a sudden gesture is made in the direction of your eyes. An infant can do all these things, and more besides.

Such innate behavior can be quite elaborate. One can visualize chains of reflexes in which the response to one stimulus will itself serve as the stimulus for a second response, which will then in

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turn serve as the stimulus for a third response, and the like. Examples of this are the elaborate courtship procedures among the sexes of some animal species: nest-building, web-building, hive-building, and the intricate patterns of care for the young.

Regrettably, the slow development of such complicated behavior patterns through evolutionary processes is lost to us. Could we trace it, we might easily see how each further link in the chain of reflexes was developed, and how each served to improve the survival chances of the next generation. Behavior patterns do not leave fossil remains, so we can only accept what we find. The necessity of accepting the end-product complications lead the overly romantic to read into the behavior of relatively simple animals the complex motivations of man. The bird in building her nest and the spider in spinning her web completely lack the forethought of the human architect and are not really suitable as subjects for little moral homilies.

Such chains of reflexes give rise to instinctive behavior (a term that is falling out of fashion). Instincts are complicated patterns of responses that share the properties of the reflexes out of which they are built. Instinct is usually viewed as a behavior pattern that is fixed from birth, that cannot be modified, that is present in all members of a designated species in an unvarying manner, and so on. Thus, a species of spider builds a certain type of elaborate web without being taught to do so, and may do so, in full elaboration, even if kept in isolation so that it never has an opportunity to see any other example of such a web. Young birds may migrate at the proper time, going to a far-distant place they have never seen and without the guidance of older members of the species.

Nevertheless, this is not absolutely characteristic of all behavior patterns usually termed as instinctive. Some birds may sing characteristic songs without ever having had the opportunity to hear other members of the species do so; but other species of birds may not. In recent years it has come to be realized that there are some patterns of behavior seemingly innate but actually fixed at some time after birth in response to some specific stimulus.

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After all, what we call birth is not actually the beginning of life. Preceding it is a period of development within an egg or womb, during which a nervous system develops to what at the time of birth is already a high pitch of complexity. Different reflexes originate at different periods in the course of this development as reflex arc after reflex arc is laid down. In the chick embryo, for example (which is easy to study), the head-bending reflex can be detected 70 hours after fertilization but the head-turning reflex only at 90 hours. Beak-movement reflexes are detectable only after 5 days, and the swallowing reflex does not make itself shown until 8 days after fertilization.

In the human embryo (less easy to study by far) there is also 'a progressive development. A reflex movement of the head and neck away from a touch around the mouth and nose can be detected in an 8-week human embryo, but such important reflexes as grasping and sucking do not appear until the embryo is at least double that age. To be sure, birth is an important turning point in the developmental process, and by the time it occurs enough reflexes must be developed to make independent life possible, or else the infant will not survive. That is self-evident. Yet there is room for more beyond bare survival.

Such continuity is taken for granted in structural development, where processes sweep past the moment of birth without a pause. The ossification of the skeleton begins before birth and continues after birth for years. The myelinization of nerve fibers begins before birth and continues afterward. Why should this not be true of behavioral development, too? The situation after birth does introduce one radical change. Before birth, the total universe is that of the egg or womb and it is therefore relatively fixed, with limited possibilities of variation. After birth, the environment expands and much more flexibility and variety in the way of stimuli are possible. The "instincts" developed after birth therefore may well depend upon such stimuli in a way that truly innate instincts do not. Chicks and ducklings fresh out of the shell do not follow their mothers out of some innate instinct that

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causes them to recognize the mothers. Rather, they follow something of a characteristic shape or color or faculty of movement. Whatever object provides this sensation at a certain period of early life is followed by the young creature and is thereafter treated as the mother. This may really be the mother; almost invariably is, in fact; but it need not be!

The establishment of a fixed pattern of behavior in response to a particular stimulus encountered at a particular time of life is called imprinting. The specific time at which imprinting takes place is a critical period. For chicks the critical period of "mother-imprinting" lies between 13 hours and 16 hours after hatching. For a puppy there is a critical period between three and seven weeks during which the stimulations it is usually likely to encounter imprint various aspects of what we consider normal f and instinctive) doggish behavior.

There is the example of a lamb raised in isolation for the first ten days of its life only. It was restored to the flock thereafter, but certain critical periods had passed and certain imprintings had not taken place. The opportunity was gone. It remained independent in its grazing pattern, and when it had a lamb of its own, it showed very little "instinctive" behavior of a pattern which we usually tab as "mother love." The loss of a chance at imprinting can have a variety of untoward effects. Animals with eyes deprived of a chance for normal stimulation by a variegated pattern of light at a particular time of early development may never develop normal sight, though the same deprivation before or after the critical period may do no harm.

It seems almost inevitable that such imprinting takes place in the human infant as well, but deliberate experimentation on such infants, designed to interfere with any imprinting procedures that may exist, is clearly out of the question. Knowledge concerning human imprinting can only be gained through incidental observations. Children who at the babbling stage are not exposed to the sounds of actual speech may not develop the ability to speak later, or do so to an abnormally limited extent. Children

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brought up in impersonal institutions where they are efficiently fed and their physical needs are amply taken care of but where they are not fondled, cuddled, and dandled become sad little specimens indeed. Their mental and physical development is greatly retarded and many die for no other reason, apparently, than lack of "mothering" — by which may be meant the lack of adequate stimuli to bring about the imprinting of necessary behavior patterns. Similarly, children who are unduly deprived of the stimuli involved in the company of other children during critical periods in childhood develop personalities that may be seriously distorted in one fashion or another.

But why imprinting? It is as though a nerve network designed to set up a behavior pattern were complete at birth except for one missing link. Given an almost certain stimulus, that final hnk snaps into place, quickly and irrevocably, with a result that, as far as we know, can neither be reversed nor modified thereafter. Why, then, not have the final link added before birth and avoid the risks of having imprinting fail?

A logical reason for imprinting is that it allows a certain desirable flexibility. Let's suppose that a chick is born with the prescribed behavior of following its true mother, a mother it can "instinctively" distinguish, perhaps through some highly specific odor it inherits and which mother and offspring therefore share. If the true mother is for any reason absent (killed, strayed, or stolen) at the moment of the chick's birth, it is helpless. If, on the contrary, the question of motherhood is left open for just a few hours, the chick may imprint itself to any hen in the vicinity and thus adopt a foster-mother. Clearly, this is an important and useful ability.

We are faced with two types of behavioral patterns, therefore, each with its own advantage. Innate behavior is certain in that it prescribes responses and avoids error, provided the environment is exactly that for which the innate behavior is suited. Non-innate behavior (or "learned behavior") is risky in the sense that if anything goes wrong with the learning process the proper

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pattern of response is not developed; but it offers the compensation of flexibility in adjusting the pattern to changes in the environment.

Imprinting is only the most primitive form of learned behavior. It is so automatic, takes place in so limited a time, under so general a set of conditions, that it is only a step removed from the innate. There are, notwithstanding, other forms of learning more clearly marked off from innate behavior and designed to adjust responses more delicately and with less drastic finality to smaller and less predictable variations in the environment.

CONDITIONING

A baby is equipped with functioning salivary glands and the taste of food will cause the secretion of saliva by those glands. This is an example of a reflex. It is developed before birth and is thereby innate. It is universal and unvarying in the sense that all babies respond to stimulation of the taste buds by salivating. And it is involuntary. Under ordinary circumstances a baby can't help salivating in response to the taste of food; and, for that matter, neither can you. This is, therefore, an unconditioned reflex. There are no conditions set for its occurrence. It will occur under all normal conditions.

The sight or smell of food will not in themselves bring about salivation at first. After an interval of experience in which a particular sight or smell always immediately precedes a certain salivation-inducing taste, that sight or smell comes to elicit salivation even in the absence of the taste. An infant has learned, one might say, that the smell of food or the sight of food means that the taste of food is about to come, and it salivates (involuntarily) in anticipation. Once this association of sight or smell with taste is set up, the response is automatic and resembles a reflex in all ways. However, it is a reflex that is dependent upon one condition; that of association. If feeding always took place in darkness, the sight of food alone would never elicit salivation, since

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its appearance would never have been associated with its taste. If a certain item of food were never included in the diet its odor would not induce salivation, even though it be a "natural" dietary item for that species. A puppy that has never been fed meat will not salivate in response to the odor of meat.

The reflex that develops in response to an association is therefore a conditioned reflex. It is as though the body is capable of hooking neural pathways together to achieve a shortcut. If faced with a situation of "particular smell means particular taste means salivation," a nerve pathway is eventually set up that will give results equivalent to "particular smell means salivation." (This somehow resembles the mathematical axiom that if a = b and b = c, then a = c.)

This has clear value for survival, since a response that is useful for a specific stimulus is very likely to be useful for other stimuli invariably or almost invariably associated with it. An animal seeking food and guided only by its unconditioned reflex is reduced to sampling everything in its environment by mouthing it. The animal will starve or poison itself, in all likelihood. An animal that conditions itself into recognizing its food by sight and smell will get along far better.

A conditioned reflex can be established for any associated stimulus, even one that does not "make sense." Conditioning is not a logical process—it works only by association. The first to experiment with artificial associations that did not make sense was a Russian physiologist, Ivan Petrovich Pavlov. Pavlov began the important phase of his career by working out the nervous mechanism controlling the secretion of some of the digestive glands. In 1889, he carried on rather impressive experiments in which he severed a dog's gullet and led the upper end through an opening in the neck. The dog could then be fed, but the food would drop out through the open gullet and never reach the stomach. Nevertheless, the stimulation of the taste buds by the food caused the stomach's gastric juices to flow. Here was an unconditioned reflex. Pavlov went on to show that, with appro-

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priate nerves cut, the reflex arc was broken. Though the dog ate as heartily as before, there was no flow of gastric juice thereafter. Pavlov obtained a Nobel Prize for this work in 1904.

By that time, however, something new had developed. In 1902 Bayliss and Starling {see p. 4) had shown that the nerve network was not the only means of eliciting a response by the juice-secreting digestive glands. As a matter of fact, they showed that the action of the pancreas was not interfered with by cutting the nerves leading to it, but that there was a chemical connection by way of the bloodstream. Pavlov thereupon struck out in a new direction, with even more fruitful results. Suppose a dog were offered food. It would salivate as a result of the taste through an unconditioned reflex; and would salivate in response to the sight and smell alone through early conditioning. But suppose, further, that each time it was offered the food a bell was rung. It would associate the sound of the bell with the sight of the food, and after this had been repeated from 20 to 40 times salivation would take place at the sound of the bell alone.

Pavlov spent the remaining thirty years of his life experimenting with the establishment of conditioned reflexes. Such conditioning can be established for almost any combination of stimuli and response, though flexibility is not infinite. Experimenters have discovered that certain experimental conditions are more efficient in producing conditioning than others. If the stimulus for which conditioning is desired is presented just before the normal stimulus — that is, if the bell is rung just before the food is presented — then conditioning proceeds most rapidly. If the bell is rung after the food is presented, or at too long an interval before food is presented, then conditioning is more difficult.

Some responses are more difficult to force into line with conditioning than others. Salivation is an easy response to adjust and an animal that salivates copiously can be made to salivate in response to almost anything associated with food. On the contrary, the response of the iris to intensity of light is extremely hard to condition to any stimulus but light. (This seems to make sense.

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The response to food needs to be highly flexible, because food can appear in a variety of guises and under a variety of conditions; but light is light, and little flexibility in response to it is either needed or desired.)

Different species vary in the ease with which they can be conditioned. In the main, animals with a more highly developed nervous system are easier to condition. They make the association of bell and food more easily. Or, to put it another way, the fact that more neurons are available in the nervous system, and that these are more complexly interrelated, makes it easier to set up new pathways.

Conditioning is distinguished from imprinting by the fact that the former is more flexible. A conditioned reflex can be established at any time and for a wide variety of stimuli and responses, whereas imprinting happens only during a critical period and involves a specific stimulus and response. Conditioning is a much slower process in general than imprinting is, and, unlike imprinting, it can be reversed.

Suppose that a dog had been conditioned to salivate at the sound of a bell and then over a period of time the bell was repeatedly rung without food being presented. The salivary response would grow weaker, and eventually the dog would no longer salivate when the bell rang. The conditioning will have been extinguished.

As is not surprising, the longer and more intensively a particular piece of conditioning has been established, the longer the time required to extinguish it. As is also not surprising, a conditioning that has been established and then extinguished is easier to establish a second time than it was the first. The nervous system, one might say, has made the new connection once, and it remains there ready to hand.

The conditioned reflex has proved to be an invaluable tool in the study of animal behavior; it can be made to yield answers that would otherwise have required direct communication with a lower creature. In the previous chapter, I said that a bee could

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not see red, but could see ultraviolet. How can this be established, since the bee cannot bear direct witness to the fact? The answer lies in conditioning. A creature cannot be conditioned to respond to one stimulus and not to another unless it can distinguish between the two stimuli. This would seem self-evident. Suppose, then, that bees are offered drops of sugar solution placed on cards. They will fly to those cards and feed. Eventually, they will be conditioned to those cards, and will fly to them at once when they are presented, even when food is not present upon them. Suppose that two cards are used, alike in shape, size, glossiness, and in every controllable characteristic, except that one is blue and one is gray. Suppose further that the sugar solution is placed always on the blue card and never on the gray. Ultimately the bee will be conditioned to the blue card only, and will fly to any blue card presented but not to any gray card. From this it can be deduced that the bee can tell the difference between a blue card and a gray card when the only known difference is color. Hence, the bee can see the color blue.

Suppose the experiment is then changed and a red card and a gray card are used, with the food always present on the red card. Finally, when enough time has elapsed to make it reasonable to assume that conditioning has taken place (on the basis of results in the blue-gray experiment), the bees are tested with red and gray cards that do not carry food. Now it is found that tbe bees fly to the red and gray cards indiscriminately. It would follow that the bee cannot differentiate red and gray. In short, it cannot see red.

On the other hand, the bee will differentiate between two cards that to ourselves seem to be identical in color but differ in that one reflects more ultraviolet than the other. If food is placed only on one of these cards and never on the other, this leads to successful conditioning of the bee. It will distinguish between the two cards even in the absence of food, though we with our own unaided eye cannot. In short, it can see ultraviolet.

In the same way, we can test the delicacy with which a dog

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can distinguish the pitch of a sound or the shape of some object, by conditioning it to that pitch or shape and tlien noting to what other pitches or .shapes it remains indifferent. A dog will distinguish between a circle and an ellip.se, for instance. Also, it will distinguish between a circle in which two perpendicular diameters are each ten units in length and an ellipse in which two perpendicular diameters are nine units and .ten units in length, respectively. It will further distinguish between sounds varying in frequency by as little as three vibrations per second. Yet it can also tie shown that the dog is completely color-blind, because it cannot be conditioned to any differences in color.

14

OUR  MIND

LEARNING

Men have in the past sometimes tended to set up a firm and impassable wall separating the behavior of man from that of all creatures other than man and to label the wall "reason." Creatures other than man we might suppose to be governed by instincts or by an inborn nature that dictates their actions at every step; actions which it is beyond their power to modify. In a sense, from such a viewpoint animals are looked upon as machines; very complicated machines, to be sure, but machines nevertheless.

Man, on the other hand, according to this view, has certain attributes that no animal has. He has the capacity to remember the past in great detail, to foresee possible futures in almost equal detail, to imagine alternatives, to weigh and judge in the light of past experience, to deduce consequences from premises — and to base his behavior upon all of this by an act of "free will." In short, he has the power of reason; he has a "rational mind," something, it is often felt, not possessed by any other creature.

That man also has instincts, blind drives, and, at least in part, an "animal nature" is not to be denied; but the rational mind is supposed to be capable of rising above this. It can even rise superior to the reflex. If prepared, and if there is a purpose to be served, a man can grasp a hot object and maintain the grasp

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although his skin is destroyed. He can steel himself not to blink if a blow is aimed at his eyes. He can even defy the "first law of nature," that of self-preservation, and by a rational act of free will give his life for a friend, for a loved one, or even for an abstract principle.

Yet this division between "rational man" and "irrational brute" cannot really be maintained. It is true that as one progresses along the scale of living species in the direction of simpler and less intricately organized nervous systems innate behavior plays a more and more important role, and the ability to modify behavior in the light of experience (to "learn," that is) becomes less important. The difference in this respect between man and other animals is not that between "yes" and "no" but, rather, that between "more" and "less."

Even  some of  the  more  complicated   protozoa — one-celled animals — do not invariably make the same response to the same i    stimulus as would be expected of them if they were literally i     machines.  If presented with an irritant in the water, such a creature might respond in a succession of different ways, i, 2, 3, 4, each representing a more strenuous counter.   If the irritant is repeated at short intervals, the creature may eventually counter with response 3 at once, without bothering to try i or 2.   It is as though it has given up on halfway measures and, in a sense, has teamed something.

And, of course, more complex animals are easily conditioned in such a fashion as to modify their behavior, sometimes in quite complex manner. Nor must we think of conditioning only as something imposed by a human experimenter; natural circumstances will do as well or better. The common rat was alive and flourishing long before man was civilized. It lived then without reference to man and his habitations. It has learned, however, to live in man's cities and is now as much a city creature as we are; better in some ways. It has changed its "nature" and learned as we have; and not with our help, either, but in the face of our most determined opposition.

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To be sure, a lion cannot be conditioned, either by man or by circumstance, to eat grass, since it lacks the teeth required to chew grass properly or the digestive system to handle it even if it could be chewed and swallowed. It is, one could say, the lion's inborn nature to eat zebras and not grass, and this cannot be changed. This sort of physical limitation enslaves man too. A man cannot "by taking thought" add one cubit unto his stature, as is stated in the Sermon on the Mount. Nor can he by mere thought decide to become transparent or to flap his arms and fly. For all his rational mind, man is as much bound by his physical limitations as the amoeba is.

If we confine ourselves to behavior within physical limitations, does the fact that behavior can be modified even in simple animals wipe out the distinction between man and other creatures? Of course it doesn't. That the gap (only man can compose a symphony or deduce a mathematical theorem) exists is obvious and incontrovertible. The only question is whether the gap exists by virtue of man's exclusive possession of reason. What, after all, is reason?

In the case of simple organisms, it seems quite clear that learning, in the sense of the development of behavior not innate, takes place through conditioning, and we are not trapped into believing that anything resembling human reason is involved. A bee has no innate tendency to go to blue paper rather than gray paper, but it can be "taught" to do so by conditioning it to associate blue paper, but not gray paper, with food. The new behavior is as mechanical as the old. The machine is modified by a machinelike method and remains a machine.

In mammals, with more complicated nervous systems than are possessed by any creatures outside the class and with, therefore, the possibility of more complex behavior patterns, matters are less clear-cut. We begin to recognize in mammalian behavior a similarity to our own and consequently may begin to be tempted to explain their activity by using the word "reason." A cat trapped in an enclosure from which an exit is possible if a lever is pushed

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or a latch is pulled will behave in a manner so like our own under similar circumstances as to convince us that it is disturbed at being enclosed and anxious to be free. And when it finds the exit we may say to ourselves, "Ah, she's figured it out."

But has she? Or is this an overestimate of the cat's mental powers? Apparently the latter. A trapped cat makes random moves, pushing, jumping, squeezing, climbing, pacing restlessly. Eventually, it will make some move that will by accident offer a way out. The next time it is enclosed, it will go through the same random movements until it once again pushes the lever or raises the latch; the second time, after a shorter interval of trial and error, the cat will do the same. After enough trials, it will push the lever and escape at once. The simplest explanation is that it has conditioned itself to push the lever by associating this, finally, with escape. However, there would seem to be also a matter of memory involved; a dim process that makes the cat discover the exit more quickly (usually) the second time than the first.

Animal memory has been tested by experiment. Suppose a raccoon is conditioned to enter a lighted door as opposed to an unlighted one. (It will get food in the first and an electric shock in the second.) Suppose it is barred from entering either door while the light is on and is allowed to make its choice only after the light has gone out. It will nevertheless go to the door which had been lit, clearly remembering. If the interval between the light's going out and the liberation of the raccoon is too great, the raccoon sometimes does not go to the correct door. It has forgotten. A raccoon can be relied on to remember for up to half a minute; this interval increases as animals with a more complex nervous system are chosen. A monkey may sometimes remember for a full day.

The English biologist Lloyd Morgan took the attitude that in interpreting animal behavior as little "humanity" as possible should be read into the observations. In the case of the cat in the enclosure, it is possible to avoid humanity just about alto-

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gether. A combination of trial-and-error with dim memory and conditioning is quite sufficient to explain the cat's behavior. The question is: How far up the scale of developing nervous system can we safely exclude humanity altogether? Memory improves steadily and surely that has an effect. We might conclude that it does not have too great an effect, since even in man, who certainly has the best memory in the realm of life, trial-and-error behavior is common. The average man, having dropped a dime in the bedroom, is very likely to look for it randomly, now here now there. If he then finds it, that is no tribute to his reasoning powers. Nevertheless, let us not downgrade memory. After all, a man does not have to indulge in trial-and-error only, even in searching for a dropped dime. He may look only in the direction in which he heard the dime strike. He may look in his trousers-cuff because he knows that in many cases a falling dime may end up there and defy all attempts to locate it on the floor. Similarly, if he were in a closed place, he might try to escape by beating and kicking on the walls randomly; but he would also know what a door would look like and would concentrate his efforts on that.

A man can, in short, simplify the problem somewhat by a process of reasoning based on memory. In doing so, however (to jump back to the other side of the fence again), it is possible that the trial-and-error method does not truly disappear but is ethereal-ized — is transferred from action to thought. A man doesn't actually look everywhere for a lost dime. He visualizes the position and looks everywhere mentally, eliminating what his experience tells him are unlikely places (the ceiling, a distant room) and shortening the actual search by that much.

In moving up the scale of animal behavior we find that modification of behavior goes through the stages of (i) conditioning by circumstance, (z) conditioning after trial-and-error, and (3) conditioning after an etherealized trial-and-error. If it seems fair to call this third and most elaborate form of modification "reason" it next remains to decide whether only human beings make use of it.

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Monkeys and apes remember accurately enough and long enough to make it seem unlikely that they can be thoroughly bereft of such etherealization, and indeed they are not. A German psychologist, Wolfgang Kohler, trapped in German southwestern Africa during World War I, spent his time working with chimpanzees and showed that they could solve problems by flashes of intuition, so to speak. Faced with a banana suspended in air and two sticks, each of which was too short to reach the banana and knock it down, a chimpanzee, after a period of trial-and-error that established the shortness of the sticks, would do nothing for a while, then would hook the sticks together to form a combined tool that would reach the banana. Chimpanzees will pile boxes or use a short stick to get a large stick, and do so in such a fashion as to make it impossible to deny that reason is at work.

At what point in the animal kingdom, trial-and-error is ethe-realized to a sufficient degree to warrant the accolade of "reason" is uncertain. Not enough animals have been tested thoroughly. If the chimpanzee can reason, what about the other apes? What about the elephant or the dolphin?

One thing is sure. Reason alone does not explain the gulf that lies between man and other animals.

REASON   AND   BEYOND

But is it fair to compare man and animals on the basis of so relatively simple an act as finding an escape route or a lost object? Can we generalize from finding a dime to reading a book? (The latter no animal other than man can do.) Some psychologists have rather believed that one could. The behaviorists, of whom the American psychologist John Broadus Watson was most prominent, tended to view all learning in the light of conditioned reflexes.

The conditioned reflex differs from the ordinary reflex in that the cerebrum is involved. The cerebrum is not completely essen-

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tial, to be sure, for a decerebrate animal can still be conditioned. Nevertheless, a decerebrate animal cannot be conditioned as specifically as can one with its cerebrum intact. If an animal is given a mild electric shock on one leg while a bell is sounded, the intact animal will eventually be conditioned to raising its leg when the bell is sounded, even without an electric shock; the decerebrate animal will respond by generalized escape attempts.

If the cerebrum is involved, then it is reasonable to suppose that as the mass and complexity of the cerebrum increases, so will the complexity and intricacy of the conditioned reflexes increase." More and more neurons can be devoted to "hooking up into circuits" that represent combinations of conditioning. More and more storage units for memory can be set aside, so that trial-

-, and-error can take place among the storage units rather than

i within the physical world itself.

I    Given enough storage units for memory and enough room for 'conditioning, one need look nowhere else to explain human behavior. A child looks at the letter b and begins to associate it with a certain sound. He looks at the letter-combination "bed" and begins to associate it with a given word which a few years

.earlier he had already succeeded in  associating with   a given

:.object.   Speaking and reading become complex conditioned responses, as does typing or whittling or any of a myriad other mechanical skills; and man is capable of all this not because he has something lower animals do not have, but because he has what they all have — only far more of it.

One might insist that the highest attributes of the human mind — logical deduction and even scientific or artistic creativ-

. ity — can be brought down to hit-and-miss and conditioning. The poem Kubla Khan, written by Samuel Taylor Coleridge, was

-, carefully analyzed in a book by John Livingston Lowes called ^The Road to Xanadu.   Lowes was able to show that virtually

* In fact, in mammals, the conditioned reflex can easily become too complex ' to be considered a reflex, and many psychologists prefer to refer to the phenomenon as a conditioned response. A collection of conditioned responses will form a habit.

urai

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every word and phrase in the poem stemmed from some item in Coleridge's past reading or experience. We can visualize Coleridge putting together all the word fragments and idea fragments in his mind (quite automatically and unconsciously) after the fashion of a gigantic mental kaleidoscope, picking out the combinations he liked best and constructing the poem out of them. Trial-and-error, still. As a matter of fact, by Coleridge's own testimony, the poem came to him, line after line, in a dream. Presumably, during the period of sleep his mind, unhampered by waking sensations and thought, played the more freely at this game of hit-and-miss.

If we imagine this sort of thing going on in the human brain, we must also expect that there would exist in the human brain large areas that do not directly receive sensation or govern response, but are devoted to associations, associations, and more associations. This is exactly so."

Thus, the region about the auditory area in the temporal lobe is the auditory association area. There particular sounds are associated with physical phenomena in the light of past experience. The sound of a rumble may bring quite clearly to mind a heavy truck, distant thunder, or — if no associations exist — nothing at all. (It is usually the nothing-at-all association that is most frightening.) There is also a visual association area in the occipital lobe surrounding the actual visual area, and a somesthetic association area behind the somesthetic area.

The different sensory association areas coordinate their functioning in a portion of the brain in the neighborhood of the beginning of the lateral sulcus in the left cerebral hemisphere. In this

* It is the existence of such association areas, without obvious immediate function that Rives rise to the statement, often met with, that the human being uses only one fifth of his hrain. That is not so. We might as well suppose that a construction firm engaged in building a skyscraper is using only one fifth of its employees because only that one fifth was actually engaged in raising steel beams, laying down electric cables, transporting equipment, and such. This would ignore the executives, secretaries, filing clerks, supervisors, and others. Analogously, the major portion of the brain is engaged in what we might call white-collar work, and if this is considered as representing brain use, as it certainly should be, theo the human being uses all his brain.

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area, the auditory, visual, and somesthetic association areas all come together. This overall association area is sometimes called the gnostic area (nos'tik; "knowledge" G), The overall associations are fed into the area lying immediately in front, the idea-motor area,' which translates them into an appropriate response. This information is shunted into the premotor area (lying just before the motor area in the frontal lobe), which co-ordinates the muscular activity necessary to produce the desired response, this activity being 6nally brought about by the motor area.

When all the association areas, the sensory areas, and the motor areas are taken into account, there still remains one area of the cerebrum that has no specific and easily definable or measurable function. This is the area of the frontal lobe that lies before the motor and premotor areas and is therefore called the prefrontal lobe (see illustration, p. 172). Its lack of obvious function is Mich that it is sometimes called the "silent area." Tumors have made it necessary to remove large areas of the prefrontal lobe without particularly significant effect on the individual, and yet surely it is not a useless mass of nerve tissue.

There might be a tendency, rather, to consider it, of all sections of the brain, the most significant. In general, the evolutionary trend in the development of the human nervous system has been the piling of complication upon complication at the forward end of the nerve cord. In passing from the primitive chordates, such as amphioxus, into the vertebrate subphylum, one passes from an unspecialized nerve cord to one in which the anterior end has developed into the brain. Also, in passing up the classes of vertebrates from fish to mammals, it is the forebrain section of the brain that undergoes major development, and the cerebrum becomes dominant. In going from insectivores to primates and, within the primate Order, from monkey to man, there has been

* Both the gnostic area and the ideomotor area are functional only in one cerebral hemisphere (usually the left, but in about 10 per cent of the cases the right) As I said earlier in the book, this existence of a dominant hemisphere is to prevent two separate sets of association-interpretations from arising, as conceivably might happen if each hemisphere were provided with its own "executive."

328     THE    HUMAN     BRAIN

a successive development of the foremost section of the cerebrum, the frontal lobe.

In the early hominids, even after the brain had achieved full human size, the frontal lobes continued development. Neanderthal man had a brain as large as our own, but the frontal lobe of the brain of true man gained at the expense of the occipital lobe, so if the total weight is the same, the distribution of weight is not. It is easy to assume then that the prefrontal lobes, far from being unused, are a kind of extra storage volume for associations, and the very epitome of the brain.

Back in the i93o's, it seemed to a Portuguese surgeon, Antonio Egas Moniz, that where a mental patient was at the'end of his rope, and where ordinary psychiatry and ordinary physical therapy did not help, it might be possible to take the drastic step of severing the prefrontal lobes from the rest of the brain. It seemed to him that in this fashion the patient would be cut off from some of the associations he had built up. In view of the patient's mental illness, these associations would more likely be undesirable than desirable and their loss might be to the good. This operation, prefrontal tobotomy, was first carried through in 1935, and in a number of cases did indeed seem to help. Moniz received the Nobel Prize in 1949 for this feat. However, the operation has never been a popular one and is not likely ever to become one. It induces personality changes that are often almost as undesirable as the illness it is intended to cure.

Even granted that the behaviorist stand is correct in principle and that all human behavior, however complex, can be brought down to a mechanical pattern of nerve cells (and hormones)" the further question arises as to whether it is useful to allow matters to rest there.

* Actually, it is difficult to deny this since nerves and hormones are the only physical*chemical mediators for behavior that we know of. Unless we postulate the existence of something beyond the physical-chemical (something like abstract "mind" or "soul") we are reduced to finding the answer to even the highest human abilities somewhere among the cells of the nervous system or among the chemicals in the blood — exactly where we find the lowest.

OUR    MIND

329

Suppose we are satisfied that Coleridge constructed the poem Kubla Khan by trial-and-error. Does that help us much? If it were merely that, why can't the rest of us write the equivalent of Kubla Khan? How could Coleridge choose just that pattern out of the virtually infinite numbers offered by his mental kaleidoscope which was to form a surpassingly beautiful poem, and do so in such a short time?

Clearly we have much farther to go than the distance the pat ^phrase "trial-and-error" can carry us. Briefly, as a change pro-• gresses there can come a point (sometimes quite a sharp one) , where the outlook must change, where a difference in degree suddenly becomes the equivalent of a difference in kind. To take an |ana!ogy in the world of the physical sciences, let us consider [ice. Its structure is pretty well understood on the molecular level. >If ice is heated, the molecules vibrate more and more until at ^8 certain temperature, the vibrations are energetic enough to ^Overcome the intermolecular attractions. The molecules then |bse their order and become randomly distributed; in a fashion, Imoreover, that changes randomly with time. There has been a "phase change"; the ice has melted and become water. The molecules in liquid water are like the molecules in ice and it is possible to work out a set of rules that will hold for the behavior of those molecules in both ice and water. The phase change is so sharp, however, as to make it more useful to describe ice and water in different terms, to think of water in connection with other bquids and ice in connection with other solids.

Similarly, when the process of etherealized trial-and-error becomes as complicated as it is in the human mind, it may well be DO longer useful to attempt to interpret mental activity in behaviorist terms. As to what form of interpretation is most useful, ah, that is not yet settled.

The concept of the phase change can also be used to answer the question of what fixes the gulf between man and all other creatures. Since it is not reason alone, it must be something more. A phase change must take place not at the moment when reason

330

THE    HUMAN     BRAIN

OUR     MIND

331

is introduced but at some time when reason passes a certain point of intensity. The point is, one might reasonably suppose, that at which reason becomes complex enough to allow abstraction; when it allows the establishment of symbols to stand for concepts, which in turn stand for collections of things or actions or qualities. The sound "table" represents not merely this table and that table, but a concept of "all table-like objects," a concept that does not exist physically. The sound "table" is thus an abstraction of an

abstraction.

Once it is possible to conceive an abstraction and represent it by a sound, communication becomes possible at a level of complexity and meaningfulness far beyond that possible otherwise. As the motor areas of the brain develop to the point where a speech center exists, enough different sounds can be made, easily and surely, to supply each of a vast number of concepts with in-    . dividual sounds.   And there is enough room for memory units    • in a brain of such complexity to keep all the necessary associa-   j

B

tions of sound and concept firmly in mind.

It is speech, then, rather than reason alone that is the phase * change, and that fixes the gulf between man and nonman. As I j pointed out on page 246, the existence of speech means that the gathering of experience and the drawing of conclusions is no longer a function of the individual alone. Experience is shared and the tribe becomes wiser and more knowledgeable than any individual in it. Moreover, experience unites the tribe throughout time as well as throughout space. Each generation need no longer start from scratch, as must all other creatures. Human parents can pass on their experience and wisdom to their children, not only by demonstration but by verbalized, conceptual explanation. Not only facts and techniques, but also thought and deductions can be passed on.

Perhaps the gulf between ourselves and the rest of living species might not seem so broad if we knew more about the various prehuman hominids, who might represent stages within that gap. Unfortunately we don't. We do not actually know at

what stage of development, or in what species of hominid, the phase change took place,"

PSYCHOBIOCHEMISTRY

The study of the human mind is carried on chiefly by psychologists and in its medical aspects by psychiatrists. Their methods and results are mentioned but fleetingly at best in this book, not because they are unimportant, but because they are too important. They deserve a book to themselves. In this book I am concentrating, as best I can, on anatomy and physiology, plus a bit of biochemistry.

The study of the mind by every means is of increasing importance in modem civilization. There are diseases of the mind as well as of other portions of the body — mental disease, in which the connection between the body and the outside environment is distorted. The message of the senses may be perceived in such a fashion as not to correspond with what the majority are willing to accept as objective reality. Under these conditions a person is said to be subject to hallucinations ("to wander in mind" L). Even where sensory messages are correctly perceived, the interpretation of and responses to those messages may be abnormal in intensity or in kind. Mental disease may be serious enough to destroy the ability of an individual to serve as a functioning member of society; and even if mild enough not to do so may nevertheless put him under an unnecessary burden of emotional gear-grinding.

As scientific advance succeeds in checking the ravages of many physical diseases, the mental diseases become more noticeable

* If it is true that dolphins have a faculty of speech as complex as that of man, then we are not necessarily the only species to have passed the phase change. The environment of the ocean is so different from that of land, however, that the consequences of the phase change would be vastly different. A dolphin might have a man-level mind, but in the viscous and light-absorbing medium of sea water a dolphin is condemned to the flipper and to a dependence on sound rather than vision. Man is not man by mind alone, but by mind plus eye plus hand, and if all three are taken into consideration we remain the only species this side of the phase change.

332

THE    HUMAN    BRAIN

OUR     MIND

333

and prominent among the medical problems that remain. It has been estimated that as many as 17 million Americans, nearly i in 10, suffer from some form of mental illness. (In most cases, of course, the illness is not severe enough to warrant hospitaliza-tion.) Of those mental illnesses serious enough to require hos-pitalization, the most common is schizophrenia (skiz'oh-f ree'nee-uh; "split mind" G). This name was coined in 1911 by a Swiss psychiatrist, Paul Eugen Bleuler. He used the name because it was frequently noted that persons suffering from this disease seemed to be dominated by one set of ideas (or "complex") to the exclusion of others, as though the mind's harmonious working had been disrupted and one portion had seized control of the rest.

Schizophrenia may exist in several varieties, depending on which complex predominates. It may be hebephrenic (hee'bee-free'nik; "childish mind" G), where one prominent symptom is childish or silly behavior. It may be catatonic ("toning down" G}, in which behavior is indeed toned down and the patient seems to withdraw from participation in the objective world, becoming mute and rigid. It may also be paranoid ("madness" G), and characterized by extreme hostility and suspicion, with feelings of persecution, At least half of all patients in mental hospitals are schizophrenics of these or other types. An older name for the disease was dementia praecox. (dee-men'shee-uh pree'koks; "early-ripening madness" L). This name was intended to differentiate it from mental illness affecting the old through the deterioration of the brain with age ("senile dementia"}, since schizophrenia usually makes itself manifest at a comparatively early age, generally between the years 18 and 28.

One common view of mental diseases is the "environmental theory," which looks upon them as unintelligible if considered in terms of the individual alone. The disorders are considered, instead, to involve the ability of the individual to relate to other individuals and the environment, and the effect of interpersonal stresses on this ability. The disease is hence a function of the

individual plus society. In favor of this view is the fact that there is no known physical difference between the brain of a mental patient and that of a normal individual. Favoring it in a more subtle fashion is the ancient view of the fundamental distinction between mind and body — the feeling that the mind is separate and apart from the body, not governed by the same laws and not amenable to the same type of investigation. The physical and chemical laws that have proved so useful in dealing with the rest of the body may be inadequate for the mind, which then requires a more subtle form of analysis.

Opposed to this is the "organic theory," which supports the biochemical causation of mental disease. This holds that what we call the mind is the interplay of the nerve cells of the body, and the mind is therefore, at the very least, indirectly subject to the ordinary physical and chemical laws that govern those cells. Even if a mental disorder arises from an outside stress it is the neurons that respond to the stress either well or poorly, and the varying ability to respond to the stress healthfully must have its basis in a biochemical difference. Favoring the organic theory is the fact that some forms of mental disease have indeed been found to have a biochemical basis. Pellagra, a disease once endemic in Mediterranean lands and in our own South, was characterized by dementia as one of the symptoms. It was found to be a dietary-deficiency disease, caused by the lack of nicotinic acid in the diet. As simple a procedure as the addition of milk to the diet prevented pellagra and its attendant dementia, or ameliorated it if already established.

The disease phenylpyruvic oligophrenia (ol'ih-goh-free'nee-uh; "deficient mind" G) is characterized by serious mental deficiency. Evidently it is the result of an inborn error in metabolism. In the normal individual, the amino acid phenylalanine, an essential constituent of proteins, is routinely converted in part to the related amino acid tyrosine, also an essential constituent of proteins. This reaction is governed by a particular enzyme, phenyl-alaninase. In the case of those unfortunates bom without the

334

THE    HUMAN     BBAIN

OUR     MIND

335

ability to form this enzyme, phenylalanine cannot undergo the proper conversion. It accumulates and is finally converted into substances other than tyrosine, substances not normal.y present in the body. One of these is phenylpyruvic acid, whence the first half of the name of the disease. The presence of excess phenylalanine, and of its abnormal "metabolites," adversely affects brain function (exactly how is not yet known) and produces the mental deficiency. Here, unfortunately, the situation cannot be corrected as simply as in the case of pellagra. Although it is easy to supply a missing vitamin, it is as yet impossible to supply a missing enzyme. However, some improvement in mental condition has been reported among patients with the disease who have been kept on a diet low in phenylalanine.

This offers a pattern for the possible understanding of the cause of other mental disorders, especially that of schizophrenia. There is always the possibility of an accumulation (or deficiency, perhaps) of some normal constituent of the body, particularly one that manifestly affects brain function and is therefore likely to be found in the brain. In addition there is the possibility of the existence of abnormal metabolites of such substances, metabolites that would themselves interfere with brain function.

The hope that some such solution may exist for schizophrenia is bolstered by genetic data. In the general population the chance of a particular individual developing schizophrenia is about i in 100. If, however, a certain person is schizophrenic, the chances that a brother or sister of his will also fall prey to the disease is about i in 7. If one of a pair of identical twins is schizophrenic, the chances that the other will become schizophrenic as well is very high, 3 out of 4, or even better. Even allowing for the greater similarities of environment in the case of brothers or sisters than in the case of unrelated persons, there would seem to be a hereditary factor involved. This would mean, according to our present understanding of heredity, an inherited abnormality in one or more enzyme systems and a metabolism that is therefore disordered in some specific manner.

The middle 1950's saw the beginning of a concerted effort to locate a biochemical cause of schizophrenia. For instance, nerve endings of the sympathetic system secrete norepinephrine (nor-adrenalin), as I pointed out on page 218, and this is very similar to epinephrine (adrenalin), which I discussed on pages 40-43. Adrenalin is an attractive target for suspicion because its function is to rouse the body to react more efficiently to conditions of stress. If mental disease is considered to result, in part at least, from the failure of the body to respond properly to conditions of psychological stress, might it be that the fault lies somewhere in the body's handling of adrenalin?

In the test tube, it is easy to change adrenalin to a compound called "adrenochrome." This is an abnormal metabolite, since it does not seem that adrenalin in the body normally passes through the adrenochrome stage. Interestingly enough, when adrenochrome is injected into normal human subjects, temporary psychotic states resembling those of mental illness are produced.

This is true of other adrenalin-like substances as well. For example, a compound called mescaline, much like adrenalin in molecular structure, is found in a cactus native to the American southwest. The mescaline-containing portions of the cactus are chewed by Indians during their religious rites in a deliberate attempt to achieve hallucinatory episodes. To the Indians, innocent of modern psychiatry, such hallucinations seem to be a window into the supernatural.

Here, then, we have a situation that could be directly analogous to the connection between phenylalanine and phenylpyruvic oligophrenia. Could it be that abnormal metabolites of adrenalin produced by people who happen to be born with a deficient supply of some enzyme or other eventually produce schizophrenia? However, since 1954, when this suggestion was first made, all attempts to locate adrenochrome or other abnormal metabolites of adrenalin in mental patients have failed.

Interest was also aroused in a chemical called serotonin. This is closely related to the amino acid tryptophan, which is an essen-

336

THE    HUMAN    BRAIN

tial component of proteins (see p. 10). This relationship is clear in the formulas given here, even for those not familiar with chemical formulas.

TRYPTOPHAN

Serotonin is found in numerous organs of the body, including the brain (only about i per cent of the body's supply is found in the brain), and it has a number of functions. Some of these, such as its ability to bring about the constriction of small blood vessels and the raising of blood pressure, have no direct connection with brain function, but it seems likely to have some connection with it in

other respects.

This was brought home sharply in 1954 when it was discovered (accidentally) that a drug called lysergic acid diethylamide could be used to produce hallucinations and other psychotic symptoms. Lysergic acid diethylamide has the same two-ring system that serotonin has (but with a considerably more complicated molecule otherwise) and appears to compete with serotonin for the enzyme monoamine oxidase. Ordinarily, monoamine oxidase brings about the oxidation of serotonin into a normal metabolite, one in which the nitrogen atoms have been removed. In the presence of lysergic acid diethylamide, the monoamine oxidase molecules are taken up by the intruder and are unavailable for the oxidation of serotonin.   Serotonin accumulates and may finally produce abnormal metabolites.  One abnormal metabolite looming as a possibility is bufotenin, a "toad poison" — that is, one of a group of toxic substances found in the parotid glands of toads.   This is

OUR   MIND            337

similar to serotonin in molecular structure and is known to induce psychotic states.

The possibility that serotonin in excess produces schizophrenia is greatly weakened, nevertheless, by the fact that a compound very closely related to lysergic acid diethylamide interferes with serotonin oxidation even more and yet produces no hallucinations. Furthermore, no abnormal metabolites of serotonin have been detected in schizophrenics.

So far, then, the various leads that have arisen in the search for a biochemical basis for schizophrenia (including some I have not mentioned) have led to a series of dead-ends. The search continues, however, and some important byproducts have resulted. There is, for instance, the development of tranquillizers. These are drugs that exert a calming effect upon an individual, relieving anxiety and inducing relaxation. They differ from older drugs used for the purpose in that they do not diminish alertness or induce drowsiness. The first tranquillizer to be introduced to the medical world (in 1954) was reserpine, a natural alkaloid found in the dried roots of a shrub from India. It seemed significant that part of the complex molecular structure of reserpine consisted of the two-ring combination present in serotonin. This significance was weakened by the introduction that same year of another and even more effective tranquillizer, chlorpromazine, which does not possess this particular two-ring combination. The tranquillizers are not cures for any mental illness, but they suppress certain symptoms that stand in the way of adequate treatment. By reducing the hostilities and rages of patients, and by quieting their fears and anxieties, they reduce the necessity for drastic physical restraints, make it easier for psychiatrists to establish contacts with patients, and increase the chances of release from the hospital.

The 1950*5 also saw the development of antidepressants, drugs which, as the name implies, relieve the severe depression that characterizes some mental patients; depression which in extreme cases leads to suicide. It may be that such depression is caused

338     THE    HUMAN     BRAIN

by, or at least is accompanied by, a too-low level of serotonin in the brain. At least the antidepressants all seem to be capable of inhibiting the action of the enzyme monoamine oxidase. With the enzyme less capable of bringing about the oxidation of serotonin, the level of that substance would necessarily rise.

A   FINAL   WORD

More and more it is becoming fashionable to look upon the brain as though it were, in some ways, an immensely complicated computer made up of extremely small switches, the neurons. And in one respect at least, that involving the question of memory, biochemists are coming to look to structures finer than the neuron, and to penetrate to the molecular level.

Memory is the key that makes possible the phase change I spoke of earlier in the chapter. It is only because human beings (even those not especially gifted} can remember so much and so well that it has been possible to develop the intricate code of symbols we call speech. The memory capacity of even an ordinary human mind is fabulous. We may not consider ourselves particularly adept at remembering technical data, let us say, but consider how many faces we can recognize, how many names call up some past incident, how many words we can spell and define, and how much minutiae we know we have met with before. It is estimated that in a lifetime, a brain can store 1,000,000,000,000,000 fa million billion) "bits" of information."

In computers, a "memory" can be set up by making suitable changes in the magnetic properties of a tape, changes that are retained until called into use. Is there an analogous situation in

* A "bit" is short for "binary digit" and is either i or o in computer lingo. It represents the minimum unit of information, the amount Rained when a question is answered simply "yes" or "no." All more complicated kinds of information can in theory be compounded of a finite number of bits. A face, for instance, or any other object can be built up of patterns of black and white dots, as in a newspaper photograph, each dot being a "bit," either "yes" for a white dot, or "no" for a black one. Our vision consists of such bits, each cell of the retina, responding "yes" for light and "no" for darkness, representing a bit. Our other senses can be analyzed similarly.

OUR     MIND

339

the brain? Suspicion is currently falling upon ribonucleic acid (usually abbreviated RNA) in which the nerve cell, surprisingly enough, is richer than almost any other type of cell in the body. I say surprisingly because RNA is involved in the synthesis of protein and is therefore usually found in those tissues producing large quantities of protein either because they are actively growing or because tbey are producing copious quantities of protein-rich secretions. The nerve cell falls into neither classification, so the abundance of RNA within it serves as legitimate ground for speculation.

The RNA molecule is an extremely large one, consisting of a string of hundreds or even thousands of subunits of four different kinds. The possible number c-f different arrangements of these subunits within an RNA molecule is astronomically immense — much, much larger than the mere "million billion" I mentioned above. Each different arrangement produces a distinct RNA molecule, one capable of bringing about the synthesis of a distinct protein molecule."

It has been suggested that every "bit" of information entering the nervous system for the first time introduces a change in an RNA molecule contained in certain neurons reserved for the purpose. The changed RNA molecule produces a type of protein not produced hitherto. When further "bits" of information enter the nervous system, they can presumably be matched to the RNA/protein combinations already present. If the match succeeds, we "remember."

This is, as yet, only the most primitive beginning of an attempt to analyze the highest functions of the human mind at the molecular level, and to cany it further represents the greatest possible challenge to the mind.

It seems logical, somehow, to suppose that an entity that un-

* The detailed structure of nucleic acids and proteins that makes such immense variability possible, and the manner in which a given nucleic acid can dictate the formation of a particular protein, is a subject of prime importance to biochemists today. There is no room here for even the beginnings erf a discussion of these matters, but you can find the details in my book The Genetic Code (1963).

34°     THE    HUMAN     BRAIN

derstands must be more complex than the object being understood. One can therefore argue that all the abstruse facets of modern mathematics and physical science are but reflections of those facets of the physical universe which are simpler in structure than the human mind. Where the limit of understanding will he, or whether it exists at all, we cannot well predict, for we cannot measure as yet the complexity of either the mind or the universe outside the mind.

However, even without making measurements, we can say as an axiom that a thing is equal to itself, and that therefore the human mind, in attempting to understand the workings of the human mind, faces us with a situation in which the entity that must understand and the object to be understood are of equal complexity.

Does this mean we can never truly grasp the working of the human mind? I cannot tell. But even if we cannot, it may still be possible to grasp just enough of its workings to be able to construct computers that approach the human mind in complexity and subtlety, even though we fall short of full understanding. (After all, mankind was able in the igth century to construct rather complex electrical equipment despite the fact that the nature of the electrical current was not understood, and earlier still, working steam engines were devised well before the laws governing their workings were understood.)

If we could do even so much we might learn enough to prevent those disorders of the mind, those irrationalities and passions, that have hitherto perpetually frustrated the best and noblest efforts of mankind. If we could but reduce the phenomena of imagination, intuition, and creativity to analysis by physical and chemical laws, we might be able to arrange to have the effects of genius on steady tap, so to speak, rather than be forced to wait for niggardly chance to supply the human race with geniuses at long intervals only.

Man would then, by his own exertions, become more than man, and what might not be accomplished thereafter? It is quite cer-

ou R   MIND

I    tain, I am sure, that none of us will live to see the far-distant time

iwhen this might come to pass.   And yet, the mere thought that such a day might some day come, even though it will not dawn on f   my own vision, is a profoundly satisfying one.

INDEX

INDEX

Abduc«ns nerve, 207 Accessory nerve, 208 Acetylcholine, 132

autonomic   nervous   system   and,

218

Achromatism, 297 Acoustic area, 177 Acoustic nerve, 208, 265 Acromegaly, 95 ACTH, 82

autonomic   nervous   system   and,

219

Addison, Thomas, 76

Addison's disease, 76

ADH, 63

Adrenal glands, 40

Adrenalin, 41

schizophrenia and, 335

Adrenergic nerves, 218

Adrenochrome, 335

Adrenocorticotrophic hormone, 82

Alanine, 10

Albinos, eyes of, 276, 277

Aldosterone, 80

Allergies, histamine and, 43-44

All-or-none law, 137

Alpha waves, 178

Amine group, 9

Amino acids, 8

abbreviations of, 11, 12 arrangements of, 14, 15, 36

Amino acids, contd.

corticotropin and, 83

glucagon and, 40

insulin and, 37, 38

MSH and, 84

oxytocin and, 64

secretin and, 14

structure of, 9

vasopressin and, 64, 65 Amphioxus, nervous system of, 144 Amygdaloid nucleus, 184 Analgesic, 228 Androgens, 100 Androsterone, 101 Anesthesia, 229 Angstrom, Anders J., 294 Angstrom units, 294 Anthropoid apes, 154 Anthropoidea, 152 Antibodies, thyrnus and, 97, 98 Antidepressants, 337 Antidiuretic hormone, 63 Apes, 154 Aphasia, 173 Appestat, 192 Appetite, 192 Aqueous humor, 283 Arachnoid membrane, 162 Arachnoid villi, 166 Arginine, 11 Aristotle, 3

346

INDEX

Arthritis, cortisone and, 80, 81 Asparagine, 11 Aspartic acid, 11 Aspirin, 228 Astigmatism, 287 Ataxia, 202 Atherosclerosis, 69 Atomic weight, 52 Auditory area, 177 Auditory association area, 326 Auditory canal, 251 Auditory meatus, 251 Auditory nerve, 208 Auricle, 249

Auto-allergic disease, 131 Autonomic nervous system, 214-19 Auxins, 90

Axolotls, thyroid hormone and, 55 Axon, 127 giant, 129

Babinski, Joseph F. F., 306

Babinski reflex, 306

Baboons, 153

Banting, Frederick G., 28

Bamum, Phineas T., 94

Basal ganglia, 184

Basal metabolic rate, 50

Basilar membrane, 257

Bats, echolocation and, 263, 264

Baumann, E., 47

Bayliss, William M., 4

Bees, color vision of, 295n, 315, 316

Behavior, innate, 307

instinctive, 308

trial-and-error, 320-22 Bekesy, Georg von, 259 Berger, Hans, 178 Best, Charles H., 28 Beta waves, 179 Betz, Vladimir, 173 Betz cells, 173 Bilateral symmetry, 141 Bile, cholesterol in, 69

gallstones and, 66

hormones and, 19 Bile acids, 70 Bile salts, 7r Bleuler, Paul E., 332

Blind spot, 290 Blindness, 280 Blood, cholesterol in, 69

glucose in, 30

life and, 1, 2 Blood-brain barrier, 167 BMR, 50

Bones, sound-conduction and, 254 Brachial plexus, 212 Bradykinin, 22

Braid, James, 231            ' Brain, 143

association areas in, 325, 326

biochemistry of, 331-39

cerebral lobes of, 171

chemical barriers in, 167

cholesterol in, 69

convolutions of, 149, 170

damage to, 163

early conceptions of, 2, 3

electric potentials and, 177-83

emotions and, 187, 188

glucose and, 168

hormone control by, 189

hormones and, 218, 219

low temperature and, 191

oxygen and, 168

size of, 156, 158

sleep and, 193

spinal, 148

ventricles of, 163, 164

visceral, 188

white matter of, 170, 183 Brain/body ratio, 158, 159 Brain stem, 197 Brain rumors, 168

EEC and, 181 Brand, Erwin, 11 Breath, life and, 1 Broca, Pierre P., 172, 188 Broca's convolution, 173 Bufotenin, 336 Butenandt, Adolf, 100, 101

Caesar, Julius, 182 Calcitonin, 61 Calcium ion, 59 Cancer, 89 Can thus, inner, 278

INDEX

347

Carbon atom, bonds of, 67, 68 Carboxylic acid group, 9 Cardiac glycosides, 73 Casein, iodine and, 51 Castration, 99 Cataract, 288 Catarrhina, 152 Caton, Richard, 177 Cats, eyes of, 289 Cauda equina, 211 Caudal anesthesia, 211 Caudate nucleus, 184 Celiac plexus, 216 Cells (s), glucose and, 30

specialization of, xv, xvi Cell body, 127 Central nervous system, 140

weight of, 170 Central sulcus, 171 Capitalization, 142 Cercopithecidae, 153 Cerebellar hemispheres, 197 Cerebellum, 145, 197

feedback and,201, 202 Cerebral hemispheres, 170

dominance in, 183, 184 Cerebral palsy, 202 Cerebrospinal fluid, 162

circulation of, 164, 165 Cerebrum, 145

motor area of, 173

weight of, 170 Cerumen, 252 Cervical nerves, 210 Cervical plexus, 212 Chalones, 20 Chemical senses, 235 Chemotaxis, 301 Chimpanzee, brain of, 154

brain/body ratio of, 158

reasoning of, 324 Chloride ion, 116 Chlorpromazine, 337 Cholecystokinin, 19 Cholesterin, 66 Cholesterol, 66

formula of, 68

myelin sheath and, 130 Cholinergic nerves, 218

Cholinesterase, 133 inhibition of, 135 Chordata, 143 Chorea, 186

hereditary, 187 Chorioid plexus, 164 Choroid, 276 Ciliary body, 283 Ciliary muscle, 283 Cisterna magna, 164 Clairvoyance, 233 Cocaine, 228 Coccygeal nerves, 210 Cochlea, 256 Cochlear canal, 257 Coelenterates,   nervous   system   of,

139, 140

Cold-receptors, 222 Coleridge, Samuel T., 325 Colloid, 49

Color (s), wavelength of, 294, 295 Color vision, 292, 294-97 Color-blindness, 296 Coma, 194

Competitive inhibition, 105 Compound eye, 273 Concussion, 163 Conditioned reflex, 313-17 Conditioning, 312-17 Cones, 289 Conjunctiva, 278 Conjunctivitis, 279 Contraceptives, oral, 108 Convolutions, 149 Cori, Carl F., 34 Cori, Gerry T., 34 Cornea, 275

transplantation of, 287 Corpus callosum, 183 Corpus luteum, 106 Corpus striatum, 185 Cortex, adrenal, 41, 76

sex hormones and, 106 Cortex, cerebellar, 197 Cortex, cerebral, 146, 170

mapping of, 173

sense perception and, 176

sensory area of, 175 Corti, Marchese Alfonso, 257

348     INDEX

Corti, organ of, 257 Corticoids, 77 Corticospinal tract, 174 Corticosterone, 78 Corticotropins, 83 Cortin, 77 Cortisone, 79

clinical uses of, 81 Cranial nerves, 205-8 Craniosacral division, 217 Cretins, 54 Cro-Magnons, 156 Cross-eyes, 282 Crusoe, Robinson, xii Crystalline lens, 283 Curare, 135 Gushing, Harvey, 83 Cushing's disease, 83 Cutaneous senses, 221 Cysteine, 11

structure of, 13 Cystine, 11

structure of, 12

2,4-D, 91

Dark adaptation, 293 Darwin, Charles, 250 Davy, Humphry, 229 Defoe, Daniel, xii Delta waves, 179 Dementia praecox, 332 Demyelinating disease, 131 Dendrites, 127 Deoxycorticosterone, 79 Descartes, Rene, 85 Diabetes insipidus, 65

hypothalamus and, 189 Diabetes mellitus, 26 Diaphragm, nerves of, 212 2,4-dichlorophenoxyacetic acid, 91 Diencephalon, 195 Digitalis, 73 DOC, 79 Dolphins, brains of, 159, 160

echolocatiori and, 264 Dostoyevsky, Fyodor, 182 Dura mater, 161 Du Vigneaud, Vincent, 64, 65

Ear(s), evolution of, 248, 249

Ear(s), contd.

external, 251

internal, 256

middle, 252

movement of, 250 Eardrum, 251 Earwax, 252 Ecdysis, 95 Ecdysone, 96 Echolocation, 262-65 EEC, 178

epilepsy and, 182 Electric eel, 124

cholinesterase and, 133 Electric organ, 124, 125 Electricity, 114 Electroencephalography, 178 Electromotive force, 121 Electrons, 116 Elephants, brain of, 159 EMF, 121 Emotions, 187, 188 Encephalitis, 143fi Encephalitis lethargica, 194 Encephalon, 143n Endocrinology, 24 Enterogastrone, 20 Enzymes, 8

hormones and, 16 Epilepsy, 181 Epinephrine, 41

effect of, 42, 43 formula of, 42 ESP, 233 Estradiol, 104 Estriol, 104 Estrogens, 104 Estrone, 104 17-ethynylestradiol, 104 Eunuch, 99, 100 Eustachian tube, 255 Eustachio, Bartolommeo, 255 Excretion, 6n External ear, 251 Exteroceptive sensations, 221 Extra-pyramidal  system,   174,   185,

213

Extrasensory perception, 233 Eye (s), color of, 276

349

Eye(s), contd.

compound, 273

lids of, 278

light focusing and, 284-87

movement of, 282, 283

nerves to, 206

watering of, 279 Eyeball, 275

interior of, 283, 284 Eyelids, 278

Facial nerve, 207 Farsightedness, 286 Fat(s), polyunsaturated, 70 Fat digestion, bile and, 71 Fechner, Gustav T., 227 Feedback, 7

cerebellum and, 200-202 Fever, 190 Fish, hearing of, 248 Fissure of Rolando, 171 Fissure of Sylvius, 171 Fissures, cerebral, 170 Flatworms, nervous system of, 140 Follicle, ovarian, 106 Follicle-stimulating hormone, 108 Foramen magnum, 197 Forebrain, 144 Fourth ventricle, 164 Fovea centralis, 290 France, Anatole, 158 Franklin, Benjamin, 114 Freud, Sigmund, 228 Fritsch, Gustav, 173 Frohlich, Alfred, 110 Frdhlich's syndrome,   110 Frontal lobe, 171 FSH, 108, 109

Galen, 113 Gall, Franz J., 171 Gallbladder, 19 Gallstones, 66 Galvani, Luigi, 115 Ganglion(ia), 184n

collateral, 216

prevertebral, 216 Gastrin, 20 General senses, 221 Geotropisrn, 300

Giants, pituitary gland and, 94 Gibberellin, 91 Gibbons, 154 Gland(s),23

adrenal, 40

ductless, 24

endocrine, 24

lacrimal, 278

parathyroid, 59

pineal, 85

pituitary, 56

pro thoracic, 96

sex, 99

suprarenal, 40

tear, 278

thymus, 97, 98

thyroid, 45 Glaucoma, 284 Glia cells, 167

Glossopharyngeal nerve, 208 Glucagon, 39

Glucose, blood content of, 30 Glucose threshold, 32 Glucose-tolerance test, 32 Glutamic acid, 11 Glutamine, 11 Glycine, 10

bile acids and, 71 Glycocorticoids, 79 Glycogen, corticoids and, 78

epinephrine and, 42 Glycosides, 73 Gnostic area, 327 Goiter, 47

exophthalmic, 49

iodine and, 47

iodine-deficiency, 48 Gonadotrophins, 108

human chorionic, 110 Gonads, 99

Gorilla, brain of, 154, 158 Grand mal, 181 Graves' disease, 49 Graves, Robert J., 49 Gray matter, brain and, 146

spinal cord and, 204 Growth, 87-94 Growth hormone, 92—94 Gyri,170

Habit, 325n

Hair, sensations and, 224 Hair cells, 257 Hallucinations, 331 HCG, 110

Head, evolution of, 142 Headache, 232 Hearing, binaural, 263 pitch and, 257-59 pressure and, 248 range of, 260, 261 sight compared with, 243—45 Heart, life and, 2 Heat, detection of, 240 Heat-receptors, 222 Helmholtz, Hermann von, 127, 295 Hemiplegia, 185 Hench, Philip S., 80 Hexokinase, insulin and, 33, 34 HGF, 39 Hibernation, 191 Hindbraiij, 144 Hippocrates, 182 Histamine, 43 Histidine, 11

formula of, 43 Hitzig, Eduard, 173 Holmes, Oliver W., 229 Hominidae, 155 Homo sapiens, 156 Hormone(s), 6

adrenocorticotrophic, 82

anterior pituitary, 57

antidiuretic, 63

destruction of, 8

enzymes and, 16

female sex, 103

follicle-stimulating, 108

gastrointestinal, 21

growth, 93

interstitial cell-stimulating, 109

juvenile, 96

lactogenic, 109

larval, 96

liiteinizing, 109

luteotrophic, 109

male sex, 100

mechanism of action of, 16-18

melanocyte-stimulating, 84

Hormone(s), contd.

membrane diffusion of, 13

molting, 96

nerves and, 133

ovarian, 103

parathyroid, 59-62

plant, 90-92

polypeptide, 14

posterior pituitary, 62-65

precursors of, 15, 16

pregnancy and, 107, 108

protein, 14

sex, 104

somatotrophic, 93

steroid, 74

synthesis of, 65

termination of action of, 7

testicular, 100

thyroid-stimulating, 57

thyrotrophic, 57

wounds, 92

Hummingbird, brain of, 159 Huntington, George S., 187 Huntington's chorea, 187 Huygens, Christian, 270 Hydrocephalus, 166 Hydrotropism, 301 Hyperglycemic-glycogenolytic factor,

39

Hyperopia, 286 Hyperparathyroidism, 61 Hyperthyroidism, 48 Hypnotism, 231 Hypoglossal nerve, 208 Hypophysis cerebri, 56 Hypopituitarism, 57 Hypothalamus, 188, 189 Hypothermia, 191 Hypothyroidism, 49

1AA, 90

ICSH, 109

Ideomotor area, 327

Imprinting, 310

Incus, 252

Indoly 1-3-acetic acid, 90

Insect(s), eyes of, 273

molting of, 95 Insectivora, 149

INDEX

351

Insomnia, 194 Instincts, 308

development of, 308-12 Insulin, differences in, 38

glucose level and, 31, 32

isolation of, 28

mechanism of action of, 33—35

molecular weight of, 35

structure of, 37 tnsulinase, 31 In termed in, 84 Internal ear, 256 Interoceptive sensations, 221 Interstitial cell-stimulating hormone,

109

Iodine, thyroid and, 47, 48, 51 Ions, 59n, 60n Iris, 276 Islets of Langerhans, 25

cell groups of, 39 Isoleucine, 10

Java man, 156 Juvenile hormone, 96

Kallidin, 21

Kallikrein, 21

Kendall, Edward C., 51, 77

Kinesthetic sense, 222

Kinins, 22

Knee jerk, 306

Kohler, Wolfgang, 324

Koller, Carl, 228

Krause, Wilhelm, 222

Krause's end bulb, 222

Lacrimal ducts, 279 Lacrimal glands, 278 Lactogenic hormone, 109 Lamprey, nervous system of, 144

semicircular canals of, 268n Langerhans, Paul, 25 Larval hormone, 96 Lateral lines, 248 Lateral sulcus, 171 Lateral ventricles, 164 Learning, 324 Lemurs, 150 Lens, 272

Lens, crystalline, 283

accommodation of, 285

transparency of, 287, 288 Lentiform nucleus, 184 Leo XIII, 100 Leucine, 10 Leyden jar, 114 LH, 109 Light, 269-71

colors of, 294

focusing of, 284—87

reaction to, 271

refraction of, 272

spectrum of, 295

wave nature of, 270 Light adaptation, 293 Lilly, John C., 160 Limbic lobe, 188 Limbic system, 188 Liver, glycogen and, 30

life and, 2 Lobes, cerebral, 171

prefrontal, 327 Lowes, John L-, 325 Lumbar nerves, 210 Lumbar plexus, 212 Lumbar puncture, 166 Luteinizing hormone, 109 Luteotrophic hormone, 109 Lysergic acid diethylamide, 336 Lysiiif, 11 Lysozyme, 279

Macula lutea, 289 Magnus-Levy, Adolf, 50 Malleus, 252

Mammals, cerebrum of, 147 Mandibular nerve. 207 Marine, David, 48 Maxillary nerve, 207 Medial nuclei, 230 Medulla, adrenal, 41

autonomic   nervous   system   and,

218-19

Medulla oblongata, 145, 195 Meissner, Georg, 222 Meissner's corpuscle, 222 Melanocyte-stimulating hormone, 84 Mefatonin, 86

1

352

Membrane, cell, 73 depolarized, 122 hormones and, 18 polarized, 121 semipermeable, 117, 118 Membrane, tympanic, 251 Memory, 325

RNA and, 338 Meninges, 161 Meningitis, 162 Mescaline, 335 Mesmer, Friedrich A., 231 Metabolism, 29 Metamorphosis, 95 Methionine, 11 Methyltestosterone, 103 Midbrain, 144 human, 195 Middle ear, 252

Midgets, pituitary gland and, 94 Milk production, 109 Miller, Jacques F. A. P., 98 Mineral ions, hormones and, 79 Mineralocorticoids, 79 Molecular weight, 13 Molting, insect, 95 Molting hormone, 96 Moniz, Antonio Egas, 328 Monkeys, brains of, 152, 158, 159 New World, 152 Old World, 153 Monoamine oxidase, 336 Morgan, Lloyd, 321 Morphine, 228 Morton, William G. T., 229 Moths, phototaxis of, 301n Motor area, 173 Motor unit, 135 MSH, 84

Miiller, Johannes, 128 Multicellularity, xv Multiple sclerosis, 131 Muscae vol it antes, 284 Muscles, nerves and, 134 reflex responses of, 305 Myasthenia gravis, 135 Myelin sheath, 129 Myoneural junction, 134 Myopia, 286

INDEX

Myxedema, 50

Narcotic, 228 Narses, 100 Neanderthal man, 156 Nearsightedness, 286 Neopallium, 147 Nerve(s), 113 abducens, 207 accessory, 208 acoustic, 208, 265 adrenergic, 218 ancient theories of, 113, 114 auditory, 208 cervical, 210 cholinergic, 218    ' coccygeal, 210 cranial, 205-8 facial, 207

glossopharyngeal, 208 Iiypoglossal, 208 lumbar, 210 mandibular, 207 maxillary, 207 mixed, 205 motor, 205 muscles and, 134 myelinization of, 131

oculomotor, 206

olfactory, 205, 206

ophthalmic, 207

optic, 206

pancreas and, 3, 4

refractory period of, 138

regeneration of, 136

sacral, 210

sciatic, 211

sensory, 205

spinal, 209-13

stato-acoustic, 208

stimulation of, 136-38

thoracic, 210

threshold stimulus of, 137

transplantation of, 136

trigeminal, 206, 207

trochlear, 206

vagus, 208 Nerve cell(s), 127

number of, 167

INDEX

Nerve cords, 140 Nerve fibers, 125

afferent, 205

efferent, 205

motor, 205

postganglionic, 215

preganglionic, 215

sensory, 205

sheath around, 129

somatic, 214

visceral, 214

width of, 128 Nerve gases, 135 Nerve impulse, 127

chemicals accompanying, 132, 133

speed of, 127-29, 131 Nervous system, 139

autonomic, 215

bony protection of, 161

central, 140, 170

peripheral, 140 Neuralgia, 207 N'eurilemma, 129 Neuroglia, 167 Neurohormone, 133 Neurohumor, 133 Neuromuscular junction, 134 Neuron(s), 127

connector, 303

effector, 303

interconnection of, 132

receptor, 303 Newton, Isaac, 270 Nictitating membrane, 278 Night blindness, 293 19-nortestosterone, 103 Nodes of Ranvier, 129 Noradrenalin, 218 Norepinephrine, 218 19-nortestosterone, 103 Novocain(e), 228 Nyctalopia, 293

Occipital lobe, 171 Oculomotor nerve, 206 Olfactory lobes, 145 Olfactory nerve, 205, 206 Ophthalmic nerve, 207 Opsin, 292

Optic lobes, 145 Optic nerve, 206 Orangutan, brain of, 154 Ossicles, 252 Otoconia, 266 Otocyst, 266 Otoliths, 266 Oval window, 252 Ovarian hormones, 103 Overweight, 192 Oxytocin, 64

Pacini, Filippo, 223 Pacinian corpuscle, 223 Pain, 227

internal, 231, 232

referred, 232 Pain-receptors, 223 Pallium, 146 Palsy. 186 Pancreas, diabetes and, 26

glandular nature of, 24, 25

nerves and, 3, 4

secretin and, 7 Pancreozymin,  19 Papillae, 235, 236 Paralysis, 185n Paralysis agitans, 186 Paramecia, response of, 302 Parasympathetic division, 217 Parathyroid glands, 59 Parathyroid hormone, 59-62 Parietal lobe, 171 Parkinson, James, 186 Parkinson's disease, 186 Patellar reflex, 306 Pavlov, Ivan P., 313 Peking man, 156 Pellagra, 333 Peptides, 13, 14 Peripheral nervous system, 140 Peripheral vision, 290 Petit mal, 181 Phenylalaninase, 333 Phenylalanine, 10

mental deficiency and, 333, 334 Phenylpyruvic acid, 334 Phenylpyruvic oligophrenia, 333 Phenylthiocarbamide, 238, 239

354     1N

Phosphenes, 291 Phospholipid molecules, 73 Photopic vision, 291 Photoreception, 272 Photoreceptors, 272, 288, 289 Phototaxis, 301 | Phototropism, 300 Phrenology, 172 Pia mater, 162 Pineal gland, 85 Pinna, 249

Pitch, perception of, 257-62 Pitt-Rivers, Rosalind, 53 Pituitary gland, 56

adrenal cortex and, 81-82 growth and, 92-95 hypothalamus and, 189 lobes of, 56, 57 sex hormones and, 108, 109

Pituitrin, 63

Placenta, pregnancy and, 107, 108

Plant(s), growth of, 90-92 responses of, 299-301 symmetry and, 141

Plant hormones, 90-92

Platyrrhina, 152

Pleasure center, 188

Plexus, 212

Polypeptide, 14

Pongidae, 154

Pons, 195

Portal vein, glucose and, 30

Position sense, 222

Posterior pituitary hormones, 62—65

Postganglionic fibers, 215

Potassium ion, 116

distribution of, 119-21

Potential, electric, 121

Precognition, 233

Prefrontal lobe, 327

Prefrontal lobotomy, 328

Preganglionic fibers, 215

Pregnancy, hormones and, 107—8 testing for, 111

Premotor area, 327

Presbyopia, 286

Pressure-receptors, 223

Primates, 149-56

Progesterone, 107

Progestin, 107 '

Prolactin, 109

Proline, 10

Proprioceptive sensations, 221

Prosecretin, 15, 16

Prosencephalon, 195

Prosimii, 150

Protein, iodinated, 51

molecular weight of, 13

structure of, 10 Prothoracic glano), 96 Psychomotor attacks, 181 PTC, 239 Pupil, 277 Pyramidal cells, 173 Pyramidal system, 174

Quadrumana, 153«

Quinine, taste of, 237

Radar, 265 Radial symmetry, 141 Rami, spinal nerve, 211 Ranvier, Louis A., 129, 130 Reflex, 303

Babinski, 306

conditioned, 313-17

crossed extensor, 305

flexion, 305

patellar, 306

stretch, 305

unconditioned, 312 Reflex arc, 302, 303 Reflex center, 303 Refractory period, 123 Regeneration, 88 Reichstein, Tadeus, 77 Reptiles, cerebrum of, 146 Reserpine, 337 Response, 298 Reticular activating system, 175, 198

sleep and, 193 Reticular area, 198 Retina, 284

structure of, 288 Retinene, 292 Rheotaxis, 302 Rhine, Joseph B., 233 Rhodopsin, 292

INDEX

355

Ribonucleic acid, 339 RNA, 339 Rods, 288 Rolando, Luigi, 171 Round window, 258 Ruffini, Angelo, 222 Ruffini's end organ, 222 Ruzicka, Leopold, 101

Saccharin, 238 Saccule, 248 Sacral nerves, 210 Sacral plexus, 212 Saint Vitus's dance, 187 Salivary secretion, 202 Sanger, Frederick, 36 Saponins, 73 Sarcolemma, 134 Schizophrenia, 332 Schlemm, Friedrich, 283 Schlemm, canal of, 283 Schwann, Theodor, 129 Schwannoma, 129 Schwann's cells, 129 Sciatic nerve, 211 Sciatica, 212 Sclera, 275 Scotopic vision, 291 Secret in, 6

amino acids of, 14

molecular weight of, 13

structure of, 8, 14 Secreti nase, 8 Secretion, 6n

endocrine, 24

exocrine, 24 Segmentation,  nervous  system and,

209

Selkirk, Alexander, xii Semicircular canals, 267 Sensation, intensity of, 226 Sense(s), chemical, 235

cutaneous, 221

general, 221

kinesthetic, 222

position, 222

special, 221

vestibular, 248, 265-68 Sense deprivation, EEC and, 179

Sense perception, 220 Sensory area, 175 Serine, 10 Serotonin, 335 17-ethynylestradioI, 104 Sex glands, 99 Sex hormones, 104

action of, 105, 106 Side-chain, amino acid, 9 Sight,   depth   perception   in,   280, 281

hearing compared with, 243—45 Simmonds, Morris, 57 Simmonds' disease, 57 Skeleton, calcium ion and, 60 Skin, cutaneous receptors on, 223

darkening of, 84 Skull, 145 Sleep, 193

Sleeping sickness, 194 Smell, 239-42

delicacy of, 242 Smell-receptors, 241 Sodium ion, 116

distribution of, 119-21 Sodium pump, 120 Solar plexus, 216 Somatic fibers, 214 Sornatotrophic hormone, 93 Somesthetic area, 175 Somesthetic association area, 326 Sonar, 265 Soul, 1 Sound, communication and, 244-46

detection of source of, 262, 263

reflection of, 262

speed of, 247 Sound waves, 246, 247

audible, 260, 261

frequency of, 247

wavelength of, 247 Special senses, 221 Spectacles, 287 Spectrum, light, 295 Speech, brain damage and, 173 Spider monkeys, 153 Spinal cord, 202

ascending   and   descending   tracts in, 213

356     IP

Spinal cord, contd.

central canal of, 163

weight of, 170 Spinal nerves, 209-13 Spleen, 2

Squids, giant axon of, 128 Squirrel-shrews, 150 Standing,   muscle   balance   in,   19"i

198

Stapes, 252

Starfish, symmetry and, 141 Starling, Ernest H., 4 Stato-acoustic nerve, 208 Statocyst, 266 Statolith, 266

Stegosaur, nervous system of, 148 Stereoscopic vision, 281 Steroid(s), 67

adrenocortical, 77 Steroid hormones, 74 Steroid nucleus, 67 Sterols, 66 STH, 93 Stilbestrol, 105 Stimulus, 298

Stomach, secretions of, 19, 20 Strabismus, 282 Stratton, Charles S., 94 Stress, ACTH and, 83 Subsonic waves, 261 Sulci, 170

Suprarenal glands, 40 Suspensory ligament, 283 Sydenham, Thomas, 186 Sydenham's chorea, 186 Symmetry, 141 Sympathetic division, 217 Sympathetic trunks, 2(6 Sympathin, 218 Synapse, 132

acetylcholine and, 134

Tadpoles, thyroid hormone and, 54 Takamine, Jokichi, 41 Tapetum, 289 Tarsier, spectral, 151 Taste, 235-39

classification of, 236

delicacy of, 237

Taste-blindness, 239 Taste buds, 236 Taurine, bile acids and, 7] Taxis, 301 Tear glands, 278 Tears, 278, 279 Telencephalon, 195 Telepathy, 233 Temperature, body, 189 Temporal lobe, 171 Testicular hormones, 100 Testosterone, 101           ' Tetanv, 59 Thalamus, 145, 185

emotion and, 187, 188

pain and, 230

sense perception and, 187 Thales, 114 Theta waves, 179 Thigmotaxis, 302 Third ventricle, 164 Thoracic nerves, 210 Thoracicolumbar division, 217 Threonine, 11 Thumb, Tom, 94 Thymus gland, 97, 98 Thyroglobulin, 51 Thyroid cartilage, 45 Thyroid gland, 45

BMR and, 50 Thyroid    hormone,    metamorphosis

and,54,55

Thyroid-stimulating hormone, 57 Thyronine, 52 Thyrotrophic hormone, 57 Thyroxine, 51, 52 Tic douloureux, 207 Tinnitis, 255 Toad poisons, 73, 336 Toadstools, 135 Tongue, taste and, 235 Touch, delicacy of, 225

hairs and, 224 Touch-receptors, 222 Toxins, 190 Trachoma, 280 Tranquillizers, 337 Transport, active, 119 Traumatic acid, 92

INDEX

357

Trees, evolution and, 150, 151 Tree-shrews, 149

rrigeminal nerve, 206, 207

rri-iodothyronine, 53

"rochlear nerve, 206

rropism, 300

frypanosomiasis, 194

[Yyptophan, 10 formula of, 90, 336

TSH, 57

Tumor, 89

Tunnel vision, 290

Tupaiidae, 150

Turgenev, Ivan,158 2,4-D. 91

"ympanic canal, 257

"ympanic cavity, 252

"ympanic membrane, 251

"ympanum, 251

"yrosine, 10 I    formula of, 42, 52

KJltrasonic sound, 261 I    echolocation and, 264 Urine, diabetes and, 26 glucose and, 32

L volume of, 65 water control and, 63 tricle, 248, 265

agus nerve, 208 Valine, 10 Vasopressin, 64 Ventricles, brain, 163, 164 Vermis, 197 Vertebrates, 144 Vestibular canal, 257 Vestibular sense, 248, 265-68 Vestibule, 248 ^ibrissae, 224

Virilism, 84

Viscera, 214

Visceral brain, 188

Visceral fibers, 214

Visceral sensations, 221

Vision, alpha waves and, 178, 179

color, 292, 294-97

peripheral, 290

photopic, 291

scotopic, 291

stereoscopic, 281

tunnel, 290

vitamin A and, 293 Visual area, 177 Visual association area, 326 Visual pigments, 271 Visual purple, 292 Vitamin A, vision and, 293 Vitamin D, bone formation and, 61

formation of, 72 Vitreous body, 283 Vitreous humor, 283 Volta, Alessandro, 115

Wadlow, Robert, 94

Walking, muscular control in,   199,

200 Water, body content of, 62, 63

hypothalamus and, 189 Watson, John B., 324 Weber, Ernst Heinrich, 227 Weber-Fechner law, 227 Whales, brain of, 159 White matter, 204 Woman, brain of, 158 Wound hormones, 92

Young, Thomas, 270, 295 Zinjanthropus, 155