Popular Science Monthly/Volume 42/April 1893/The Correlation of Structure, Action, and Thought
|THE CORRELATION OF STRUCTURE, ACTION, AND THOUGHT.|
By T. LAUDER BRUNTON, M. D., F. R. S.
Mr. President and Gentlemen: Allow me to return you my most grateful thanks for the honor which you have done me in asking me to address you to-night. I believe that there are none here excepting myself who can understand how grateful I feel, because no one else can know how much I owe to this society. I have been compelled during my life to do a good deal of speaking and of writing, and yet these are the two things which above all others I dislike and for which I am naturally entirely unfit. Had it not been for the training which I received in this society I do not think that I should ever have been able to speak in public at all. In relation to speaking and writing, I often recall an anecdote told me by my poor friend the late Dr. Milner Fothergill, regarding a beaver which an American said he had chased so hard that it had been forced to climb up a tree to escape him. "But," said his hearer, "beavers can not climb trees." "Well," replied the American, "I guess this one had just got to." Now this society played to me the part that the American did to the beaver and forced me both to speak and write, and I am therefore very grateful to it. My first attempt at writing was the dissertation which the rales of the society demanded, and my first attempt at speaking was made in this room when I stammered out half a dozen words, each one broken into bits by the palpitations of my heart, and then thankfully sat down.
But it is not only in speaking and writing that I owe my training to the Royal Medical Society of Edinburgh, I owe to it also my first initiation into scientific methods—my first instruction in scientific skepticism. I well remember that on one occasion a member made a certain statement; he had no sooner sat down than he was challenged by my friend Dr. John Wyllie. The first member again rose to his feet and maintained that his statement was true, and that his facts were correct because Professor So-and-so had said so. Again Dr. Wyllie rose, and with the simple question, "But is Professor So-and-so right?" swept away the ground from under his opponent's feet and gave me a new insight into scientific evidence. Previously I had been inclined to accept all the dicta of the professors as gospel truth, but from that time onward I accepted them only with the proviso that Professor So-and-so might possibly be wrong. Training like this, gained by a student in the discussions at the meetings here, is of the utmost possible importance as supplying a valuable part of medical education and complementing the instruction which he gains in the lecture rooms; it enables him to sift the statements which he there hears and to assimilate them in his own mind, so that they become as it were part of himself, and afford him a basis of knowledge upon which he not only can act in daily life, but from which he may advance onward and benefit both his profession and the world at large by new discoveries. This training is so invaluable that I should look upon anything which would interfere with it as detrimental to the student; for a little knowledge, like a little food, if well assimilated, is more useful than an undigested mass, which may be not only useless but positively injurious.
The numerous discoveries which have been made during the twenty-nine years which have elapsed since I first took my seat in this hall as a member of the society have tended to increase the mass of facts which the student has to learn; and the numerous examinations have tended to foster a system of cramming which is totally distinct from that of true education. For the purpose of examination the student is tempted to load his memory with many details and to learn by heart statements which may or may not be true, simply for the purpose of committing them to paper and thus gaining good marks in competitive examinations without considering in the least whether these statements are true, or whether the facts, so called, are likely to help him at all in his future life. The period during which I regularly attended the meetings of this society was a transitional one, because the number of examinations, competitive and professional, was then beginning to increase. I trust it is not true, but I have heard that since my time the examination incubus has been weighing even more heavily upon men than it did then, and has been interfering to some extent with the activity of the discussions in this society. Yet even if it were true it can hardly be wondered at, for it seems to me that we are living at a period which is not only one of the utmost activity, one of the most startling progress, and one of the keenest excitement for all engaged in research, but at the same time it is one of the utmost difficulty for all those who are engaged in the study of medicine, surgery, and the allied sciences. For the number of facts is not only enormously great, but is daily increasing at a rate which threatens to make it almost impossible for any ordinary memory to retain them all. Yet the darkest hour is that before the dawn, and I believe that shortly medical study will become very much easier. The great difficulty that the student has in remembering facts is that they are isolated and not co-ordinated together. In a book on memory which I once read the writer summed up his whole science in one sentence: "Observe, reflect, link thought with thought, and think of the impressions." This is easy to say but not so easy to do, and it is the difficulty of linking thought with thought that makes the tax upon the memory of the medical student so exceedingly great.
Now it seems to me that one of the objects which this society should set before itself should be not only that of training its members in the art of speaking and writing, of sifting facts and criticising statements, but of linking together and co-ordinating the data which they are called upon to recollect. When the science of astronomy was younger and the earth was supposed to be the center of the universe, the motions of the planets were known with sufficient certainty to calculate eclipses, but they could only be brought into conformity with their supposed relationship to the earth as the center by the most cumbrous system of hypotheses, and by ideas of cycles and epicycles which must have burdened the astronomer's memory to the last degree. So soon, however, as the sun and not the earth was recognized to be the center of our system the whole of the observed facts were seen to be in complete harmony, and the relationship, comparatively speaking, as simple as A B C. In our own time we have seen somewhat similar occurrences in regard to the relationship of animals and plants, or I might shortly say, of all living creatures to one another. It used to be assumed that the highest plants and highest animals were to be compared together, but all attempts to make this comparison rationally were unsuccessful; and it was only when an old member of this society, Mr. Charles Darwin, pointed out that animals and plants had sprung from one common ancestor and had diverged in different directions that the various relationships became intelligible. I well remember that when learning botany it puzzled me greatly to understand why the shape of the ovary, the nature of the ovule, and the position of the embryo should be such important characters in determining the genus of plants, and I devoutly wished that plants had been made in such a way that one could settle their nature by characters visible to the naked eye and not requiring a pocket microscope.
|Fig. 1.—Chick.||Fig. 2.—Tortoise.||Fig. 3.—Hog.||Fig. 4.—Man.|
But the reason for all this at once became evident when the Darwinian doctrine showed that it is in these embryonic characters that relationships are to be discovered and that it is in later development that differences occur. As Haeckel has shown, the embryos of the fowl, the tortoise, the hog, and the man, are all nearly alike in the early stages of feetal life (Figs. 1, 2, 3, and 4), utterly different as these creatures may be when they have attained their full development—the Darwinian doctrine has thrown a flood of light on the relationship of plants and animals, and shows us that when animals have got as it were on the wrong track, however far they may go in it, they never come to anything very good.
Nobody expects much of a jellyfish. Its soft, pulpy substance is incapable of anything but the simplest movement, and no animal that has not something hard to steady it can greatly excel the jellyfish. The soft mollusks which use their hard casing only for protective purposes, like the oyster and the snail, are bound to stay low in the scale of existence, and the highest mollusk (the octopus) appears to be striving after something better, but only by the aid of an attempt at a skeleton—the so-called cuttlefish bone. But this has no joint in it, and even the octopus does not amount to much. Articulata with their jointed skeletons have reached such a pitch of social organization as to be held up for examples to mankind, and ants and bees are regarded by some as almost the mental equals, if not the superiors, of some of the savage tribes of mankind. But the outside skeleton is a sore disadvantage, for the animal must either remain without growing in
Fig. 5.—Section of Head of Femur, to show the arrangement of the fibers of bone so as to give strength to it. (From Donald Macalister.)
size, or else it must be periodically cramped for room, and periodically burst its shell, leaving itself naked, weak, and defenseless. The right thing to do is evidently to do like the vertebrata, and have the hard parts inside, and the soft parts outside; but the relationship of these parts is a sore task upon the student's memory, and to many a one anatomy is a burden too heavy to be borne, and the unfortunate youth, is forced by it to leave the study of medicine and turn his attention to some easier pursuit.
Now, I think that with a little trouble one may find a way of linking anatomical relationships together in a more rational way than that of "Bodfi," a word which in my student days was used as a mnemonic to describe the form of the hippocampal convolution of the brain—backward, outward, downward, forward, and inward. The word also served to describe the course of the ribs, but Dr. Anderson Stewart has shown us how naturally the peculiar twist the ribs take in a man arises from his upright position. Taking a circular steel hoop, and simply hanging it up by one side, he shows that it assumes an oval shape, like that of the thorax of animals going upon four legs and whose ribs hang vertically from the spine. On raising this up by one point it becomes twisted upon itself and takes precisely the peculiar bend which the ribs possess in man. The advantage of a naturally jointed skeleton is so obvious that I need not further discuss it here, nor need I discuss the texture of bone which has been so admirably treated of by my friend Dr. Donald Macalister, of Cambridge (Fig. 5).
The ligaments and the joints were to me most puzzling until Dr. Joseph Bell pointed out to me how very simple they were. What is wanted in a joint is a capsule to go round it so as to hold the ends of the bones together and prevent the synovial fluid from oozing out. If the bones have to move freely in all directions they must have a ball-and-socket joint, as at the shoulder (Fig. 6) and at the hip, and there you will have a simple capsule because it can not be particularly strengthened at one point or another without interfering with freedom of movement. In the case of a hinge-joint, such as those of the fingers or toes, elbows or knees, you will have the capsule remaining thin at the front and back so as to leave the movement free, but you will have it strengthened at the sides so as to tie (Fig. 7) the bones more firmly together, and the stronger parts are called lateral ligaments. If several bones have to be connected, each one must be tied first of all to the one nearest it, and then two or three must be tied together at a time, and in this way we get the network of ligaments which we find at the wrist and tarsus (Fig. 8). The same thing is true of muscles, and, as Prof. Goodsir used to point out, the muscles of the back, so perplexing at first, are really quite simple in their arrangement. For each of the spinal vertebræ has to be bent and straightened and has also to rotate more or less upon its neighbors, so as to allow the upper part of the body to swing round upon the lower. We have, therefore, muscles going from the spine of one vertebra to the spine of the next, and then muscular strips stretching over a few and then over many vertebræ, so as to straighten the spine either in part or whole, as the movements may require. A similar arrangement holds good for the muscles passing from the spines to the lateral processes and which rotate the vertebræ on one another.
But if we are to group the muscles and nerves of the body into one easily remembered whole, we must see what is the chief function to be subserved by them, what is the center of the little universe which they compose. The function of most imperious necessity is respiration. A man may starve himself to death, but he can not kill himself by holding his breath. He may refuse food, but can not refuse air. In the child the function of respiration is the first which evidences itself after birth, and the muscles which subserve it are more fully developed and more perfectly innervated than others. The nerve channels which supply them are, as it might be termed, more deeply grooved than others, and it is along these channels that superabundant energy overflows in the movements of laughter which evidence joy. This has been very fully and wisely explained by Herbert Spencer in his essay on Laughter. But the great poet, whose recent death the whole civilized world is now deploring, has classed together in a few pregnant words the channels through which the overflow of energy may run in their proper order. In describing the joy evinced by a baby on seeing its mother, Tennyson says it
A blind and babbling laughter, and to dance
Its body, and reach its failing innocent arms
The very parts which attain to the highest development in adult age, and are capable of the finest and most dexterous movements, are the last to develop, and in infancy they are well described as "lazy lingering fingers." They take no part in the function of respiration, but they are of the utmost utility in the function which comes next to respiration in importance—namely, that of nutrition. The animal has to be fed, and all the arrangements of the limbs are more or less subservient to this primary object. In a fish the muscular masses at both sides of the spine bend the posterior part of the body and the tail alternately to one side or another, and so the animal is propelled through the water in search of food. No doubt these same muscles help it to escape danger, but their primary object is to obtain food; and if there be great hunger all animals will strive to feed, whatever be the risk they run in doing so. The movements of fish are simple compared|
|Fig. 9.—Diagram of the Motor Centers in the Brain. (Modified from those of Ferrier and Horsley.) The motor centers have been numbered so as to represent the successive actions in seeing, taking, and eating the apple, etc.: 1. Eve sees the fruit (eyes turn to opposite side). 2. Looks more eagerly at it (head and eyes turn). 3. Turns toward it (head to opposite side). 4. Puts forth her hand to take it (a, movements of shoulder; b, of elbow; c, of wrist; d, of fingers). 5. Luxuriously shuts her eyes, so as to enjoy the sweet morsel more thoroughly. 6. Eats the apple. 7. Picks out and throws away the refuse (d, movements of fingers; e, of index; f, of thumb; a, b, c, as in 5). 8, 9, 10, 11. Went and got another for Adam (8, movements of hallux; 9, of small toes; 10, of knee and ankle; 11, of hip).|
with those of animals with limbs, and especially with those of man. Yet the arrangements of man's body are equally adapted with those of the fish for obtaining food.
There are two prevalent ideas regarding the origin of man. One is that he started full grown and perfectly developed from the dust of the ground, and lived in a garden which he "dressed and kept." The other is the Darwinian one, that man is developed from an arboreal animal like the monkey, though lower than the monkey. It matters not which of these ideas we take, because they perfectly agree that primitive man lived at first in a kind of paradise where he was not exposed to the attacks of wild beasts, and where he fed on the fruit which he plucked from the trees around him. The story of Adam and Eve has got the advantage of not only being more poetical, but it is very much more easy to discuss the actors in the scene by the names of Adam and Eve, than by the terms "male" and "female frugivorous animal."
Let us take then the story from Genesis. One day Eve went into the garden of Eden—saw an apple upon a tree—plucked it, ate it, and then went to get another for Adam. In trying to analyze the muscles concerned in these acts, the easiest way is to go to your bedroom, strip off your clothes, imitate Eve's action, and as you do so, feel out the individual muscles as they contract under the skin. This plan of learning the muscles is one which I used to follow as a student of anatomy, and I found it a very useful one indeed. If you do this you will find the muscles of the neck, shoulder, arm, forearm, and hand contracting successively or together in co-ordinated movements, which are beautifully adapted to the purposes just mentioned. We might take the muscles which produce these movements one by one, but I think it is easier for the purpose of grouping them, though not so good for the purpose of study in your own room, to consider first of all the motor centers in the brain from which the stimuli proceed. Before proceeding to consider these I wish to draw your attention to the errors into which one may fall regarding the action of muscles as well as of the motions of the planets by regarding them from a wrong point of view. Thus, the action of the tensor vaginæ femoris is usually said to be that of rotating the thigh inward upon the body and thus turning the foot and toes inward also, an action which is denounced in all calisthenic exercises. But this muscle was not introduced into the body for the sole purpose of plaguing drill sergeants and dancing masters. As the late Prof. Sharpey used to point out, we ought to look its action from the leg as a fixed point, and then we discover its true uses at once. Place your hand at the side of the hip over the muscle and march forward. You will then find that when one foot is planted firmly on the ground the corresponding muscle becomes tense whenever you lift the other leg and try to advance it. Whenever the other foot is raised the muscle rotates the body outward on the fixed thigh and thus brings the center of gravity of the person over the resting foot. If it were not for these muscles we should run a risk of falling down as we lifted one leg instead of balancing ourselves with comfort upon that one which is resting upon the ground.
But we may now pass away from the muscles and nerves to the nervous centers from which they receive their stimulus to action, and whatever doubt may exist in regard to the adaptation of the muscles to the peripheral nerves and the action of plucking and eating the apple, I think there can be no doubt at all that such an arrangement exists in the motor centers of the brain. These centers were localized in the monkey by Ferrier, and it is the difficulty I have had in remembering their position that has led me to arrange them in accordance with some definite movements in a series of actions to which I have found they corresponded. If we start from the posterior part of the second frontal convolution, pass upward along it and then across to the ascending frontal convolution, follow this downward parallel to the fissure of Rolando, and then turning the end of this fissure ascend again upward along the parietal convolution which lies behind the fissure, we find (Fig. 9) that the centers are arranged in the very order required for looking at the apple, stretching out the hand to take it, bringing it to the mouth, separating the seeds and throwing them away. The aim and object of the whole series of actions is to eat the apple, and we find that the centers for doing this are situated exactly where we should expect them—at the very end of the fissure of Rolando. In Ferrier's description we know that the movement which brings the hand to the mouth appears to be repeated on both sides of the fissure of Rolando, but it appears that the part anterior to the former would bring the hand to the mouth with the apple, while the part situated behind the fissure of Rolando would throw the remnants of it away. And here comes in a very interesting point: In order to complete the series of actions necessary for Eve to go and get another apple for Adam, you require movements of the leg (Fig. 10), and these are not fully represented on the surface of the brain. But they have been found by Horsley and Schäfer exactly in the place where, according to our idea, they ought to be, at the marginal convolution connecting the first and last centers of which we have just spoken and thus completing the circle of action.
Here I would like to draw your attention to the fact that great painters like great poets often appear to see more than ordinary mortals, and in his lovely picture, The Fall of Man, which is painted on the walls of the Loggia of the Vatican in Rome, Raphael seems to have almost forestalled the results of physiological experiment. In the mental picture of the scene which most of us must have formed for ourselves it is probable that it did not occur to many of us to pay any attention whatever to the movements of the great toe, and yet in Horsley's diagram of the cortical centers that for the hallux comes forward most prominently, and, as you will see from Raphael's picture (Fig. 15), Eve's foot is raised, and the great toe both in her foot and that of Adam is brought into what one would think rather too violent action. In the action of plucking and eating the fruit there is no break between the eyes, head, and arm, and that of the mouth and tongue, and in the usual process of eating the actions go on which are necessary simply to repeat the process of plucking and eating. Again, too, in the dog the arrangement is quite different (Fig. 11), and yet it is exactly what one would expect from the different necessities of the animal. In the frugivorous animal the motions are pluck and eat, pluck and eat; but in the carnivorous animal a long chase after the prey is necessary before the animal can bring the jaws into action, and in the dog accordingly we find that the movements of mastication, instead of being arranged in linear series with those of the limbs, are represented at a spot which is somewhat removed from them. In the cortex the centers are so far apart as to be distinguishable from one another; but as the nerve fibers which pass downward from them to the base of the brain become closely crowded together in the internal capsule, localization is more difficult (Fig. 12), although Horsley and Beevor have found generally that the arrangement of the fibers from before backward corresponds to the arrangement of the centers just described. But as the nerves pass out from the spinal cord to reach the muscles they again become separated and, as Ferrier and Yeo have discovered, the motor roots which enter into the brachial plexus are arranged with a view to definite co-ordinated movements. Now, this plexus has been to me, and I think to many others, a perfect perplexity, both in its anatomy and physiology. Yet, if we take it from the same point of view as we have taken the motor centers, it becomes comparatively simple. We must not forget that, although the monkey is so much like man that we can draw most useful deductions regarding human physiology from experiments on these animals, we must not transfer without more ado the results of these experiments to man in their entirety. We must remember that man, although formerly a frugivorous and probably more or less arboreal animal, is now very different from a monkey, and experiments in the laboratory must be compared with and corrected by those experiments which disease makes upon man in producing localized palsies. I think it very probable that many here would find it difficult to answer the question, What are the movements which result in the monkey from stimulation of the fifth cervical nerve?—nor might he be able to remember them six months hence even if he learned to-night that they consist in the shoulder and arm being raised upward and backward, the humerus rotated outward, the forearm flexed and supinated, the wrist extended, and the tips of the fingers flexed. But he would find it easy enough to remember them, not for six months only, but for the rest of his life, if he were told that they were simply those required to raise the hand in such a way as to grasp an apple hanging straight above him. If you go through these movements you will find that your first impulse is to take a slight breath, which is chiefly effected by the diaphragm, and on looking at the brachial plexus you find that the first branch which is given off from the fifth nerve is a filament to the phrenic (Fig. 13). Then, just as you proceed to raise your shoulder, you take a still deeper breath, and this, too, is represented in the plexus by the posterior thoracic nerve, starting from the fifth and sixth nerves and going to the serratus magnus, which has little power to raise the ribs and act as an inspiratory muscle while the shoulder is depressed, but will
|Fig. 14.—Expulsion from Paradise. (After Raphael.) The position of Eve's right hand shows the action of the seventh cervical nerve.|
do so when the arm is raised. If your hand is hanging by your side, you will find the shoulder slightly drawn backward by the rhomboid and the arm rotated a little outward by the infraspinatus, which is supplied hy the suprascapular nerve. Next, you raise your arm, and as you do so you will find that unconsciously you bend it and turn it out, you extend the wrist and flex the fingers. The raising of the arm and turning it out is effected by the deltoid and teres minor, which are innervated by the circumflex nerve, while the shoulder is still further raised by the trapezius, which gets its nervous supply from a higher source—the spinal accessory. The biceps and other flexors of the arm receive their supply through the musculo-cutaneous nerve from the outer cord. In the movements of the wrist and fingers the fifth and sixth nerves appear to co-operate, and those of the fingers are chiefly due to the sixth. The supinators and extensors of the wrist, fingers, and thumb get their nerves from the musculo-spiral or its interosseous branch. To resume, the fifth and sixth cervical nerves raise the shoulder, flex the forearm, and extend the wrist. The nervous energy passes from them along the upper trunk and outer cord of the brachial plexus to the flexors of the forearm, while the impulses to raise the shoulder, rotate the humerus, and extend the wrist and fingers travel chiefly through the posterior cord by the musculo-spiral nerve and its interosseous branch to the extensors of the wrist and digits. From the fifth and sixth cervical nerves we make a jump to the first dorsal, which has an exactly opposite action. The movements it produces are that the hand closes firmly upon the apple, the wrist is twisted round into the prone position and flexed to the ulnar side. The forearm is extended, and the upper arm is retracted in the manner required to pull the apple from the tree. In these movements, if you put your hand upon your chest, you will find that the pectoral muscles are largely engaged, and they receive their nerves partly from the internal cord of the brachial plexus. Flexion to the ulnar side is produced by the ulnar nerve, and the dragging of the arm down is effected by the subscapular, teres major, and latissimus dorsi muscles, which are supplied by the subscapular nerves, and the triceps by which the arm is extended gets its nerve supply from the musculo-spiral. But these movements, especially if executed forcibly, as they would be if the apple were firmly attached, would bring the hand below the level of the mouth, and the prone position would keep the apple away.
We must now go back to the sixth cervical nerve, which we find will rectify this action, for it raises the arm inward and upward with the forearm flexed, so as to bring the hand to the mouth, supinated, and with the wrist and basal phalanges extended, so as to present the apple comfortably for eating. In effecting this movement the nervous impulses travel by the posterior thoracic, circumflex, musculo-cutaneous, musculo-spiral, and median nerves to the serratus magnus, deltoid, biceps, brachialis anticus, supinator longus, and extensors of the wrist and basal phalanges. The position of Adam's left hand in Raphael's picture shows this action in its middle stage, before it has carried the hand to the mouth. The few last phalanges of his fingers are flexed, and we may suppose that the flexion is effected by means of the median nerve, but it is just possible that their flexion may be due to mechanical pulling on the tendons by the extension of the wrist and basal phalanges just as the hand is opened in the well-known schoolboy trick by bending the wrist forcibly inward, and thus mechanically stretching the extensor tendons of the fingers. In this picture the action of the serratus magnus muscle in drawing
|Fig. 15.—The Fall of Man. (After Raphael's picture in the Loggia of the Vatican, Rome.) The position of Eve's left arm illustrates the action of the fifth cervical nerve, and that of her left hand the commencement of action of the first dorsal nerve. The position of Adam's left arm shows the action of the sixth cervical. The action of the hallux is well shown in Eve's right and Adam's left foot.|
forward the shoulder and rotating the scapula so as to raise the shoulder is well seen, and the action of the muscle appears almost exaggerated. We have already found that it gets a branch from the fifth nerve as well as from the sixth. We may fairly suppose that the branch from the fifth is the channel for the impulses which cause the muscles to act as an inspiratory muscle when raising the arm to pluck the apple, while that from the sixth serves to excite the muscle to pull the shoulder forward. Now, here we have got, apparently, the movements required for plucking the apple and conveying it to the mouth, and yet we have got two nerves which seem superfluous—the seventh and eighth cervical. We may suppose the seventh to be brought into play later on, when the first pair recognized their nakedness, for its action in the monkey is to bring the hand over the pubis in the position of Eve's, as represented by Raphael in the Expulsion from Paradise (Fig. 14). We can not in this scheme find a place for the eighth nerve in the entirety of its action, as observed in monkeys, but the first part of the movement which it produces may be used in throwing away the refuse of food.
The mere fact that I have been unable to work this last nerve properly into this scheme shows you how imperfect it is, yet I trust that, as an attempt to hang together the facts—anatomical and physiological—it may not be without service as an aid to your memories, and still more as an inducement to you to find out the true relationships of the different parts of the body.
- Inaugural address delivered at the Royal Medical Society of Edinburgh on October 21, 1892. Abridged from the London Lancet.