fixed, the other free; others, like the frog's egg, have the fresh arterial blood led to one half only, while the other half must do with what the other leaves. In both cases one pole is supplied with more oxygen than the other, and thus a gradient in degree of oxidation will be established, the processes of life working more quickly at one end than at the other.

Furthermore, it is found that the structures and organs which are found at the more active end of the gradient are relatively independent, and in some degree dominate the rest. We may again find in the flatworms a striking example. The more active end of the animal is the head, endowed with simple eye-spots and a rudimentary brain; the mouth is near the center of the body, at the end of a long protrusible organ, the pharynx, which is used to capture prey; the rest of the body is filled up with the branched digestive, excretory, and reproductive systems, together with muscles and

nerves.

These animals have an extraordinary power of regeneration. Chop them into fragments, and most of the pieces will remodel themselves into miniature whole worms. However, complete regeneration does not always occur, and if the body is cut across at different levels, a new head is more likely to grow from a cut near the head end than from one farther back. Let us consider two pieces of equal size cut out of one of these animals in such a way that piece A includes part of the body behind the head and in front of the pharynx, while piece B is behind the pharynx and has the tail cut off from it. Now, whether or not piece A forms a head, a new pharynx will form in its center. But in piece B results

will differ according as a head is formed or not. If it is formed, a pharynx will appear. If it is not, it will not appear. In other words, each region of the body appears to influence the development of the parts behind it. Piece A was from in front of the pharynx, and can cause a new pharynx to grow; but piece B is from behind the pharynx, and cannot do so unless a new head rises on it.

Once a head is formed in a piece, the other organs of the body will arise in their proper places; and thus we can call the head the high end of the axial gradient, dominant over all the rest of the body.

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From studies on the lower animals, then, we come away with two fundamental ideas. First, that old age depends on internal state, not on lapse of time; secondly, that an organism can be thought of as a system in which, as in society, one part is dominant over the rest. Let us now jump to the higher forms, and see whether these ideas help us to a better understanding or a better control of our own nature.

The higher animals, such as birds or mammals, differ from the forms we have been considering in two chief ways. They possess an enormously better developed brain, and they are much more independent of their environment, much more self-regulating. To deal only with the second point, they have the power of regulating the temperature of the body, come cold, come heat, within a degree or so. The chemical constitution of the blood is kept constant with an almost alarming accuracy; for instance, an increase of one part of the acidity-producing hydrogen in one hundred billion parts

of blood will cause an increase in the rate of breathing which, by washing carbonic acid out through the lungs, will restore acidity to the normal. Not least, the rate of growth and of differentiation, the rate of working of the whole machine, the quality of much of the psychic side of life, are kept constant by the secretions of the ductless glands, such as the thyroid and pituitary.

The thyroid is as the draft to the fire: more thyroid secretion, and you burn up quicker; less, and you are sluggish in mind and body alike. The pituitary in part regulates growth, especially the growth of bones; oversecretion of pituitary in childhood produces the lanky giants one sees at circuses. The pineal, the strange gland on the top of the brain, once supposed to be the seat of the soul, now shown to be derived from an original third eye, possibly determines the time at which sexual maturity begins. The secretion of the interstitial cells in the generative organs brings about the growth of most secondary sexual characters, such as deep voice and beard in man, and arouses the sexual instincts from their slumbering potentiality in the brain.

The higher animals, too, on the whole are bigger and live a longer time than the lower; and instead of growing continuously, they reach a condition, the adult state, in which they continue for most of their life without notable changes of size or form. The adult state is a state of balance, in which the man or animal spins on its way like a sleeping top; but the balance is not a comparatively simple affair of mechanics, but a chemical balance, in which is involved the effect of a great many secretions of various tissues on

the rest of the body and on one another. The analogy of the spinning top, however, helps in one respect. The top has a gyroscopic action, and efforts to tamper with it meet with resistance. So, too, in the mammalian body every effort to tamper with the self-regulating machinery meets with resistance. Attempt to raise the body temperature, and the sweat glands bring it down; attempt to alter the chemical constitution of the blood, and the kidneys prevent it.

When we speak of high or low organisms, indeed, one of the chief points constituting the distinction is this very fact that the higher organism possesses self-regulating apparatus which the lower do not.

Now, the strange facts of tissueculture show that even in mammals most of the parts of the body are potentially immortal, and that it is only the system as a whole which is doomed to death. Harrison at Yale, Carrel in New York, Champy in France, and other workers have demonstrated that fragments of living substance can be taken out of the body and grown in special culture media. After they have grown for a certain time, they must be transplanted to another portion of fluid; but if this is properly done, they can continue not only to live, but to grow for an apparently indefinite time. In any case, pieces taken from an embryo chick have now been cultivated for longer than the ordinary span of life of a fowl, and, what is more, their rate of growth has not slowed down. If this procedure had been known to primitive man, we should perhaps have found some nations seeking to keep their dead from corruption not by mummification, but by tissue-culture. In the adult body, however, many

kinds of cells no longer multiply. Chief among these are the nerve-cells; and it is probable that these, in the state in which they occur in the fully formed brain, are incapable of reproduction. Old age in one aspect is, then, a wearing out of the brain-cells. Slight errors of diet, worry, infections, fatigue, are inevitable in life, and have a gradually cumulative effect upon the cells, diminishing their power of recovery.

In the same sort of way the general processes of the body, and especially of the ductless glands, seem to suffer as time goes on. Once one begins to fail, all the rest are affected; and what one might call the "virtuous circle" of healthy maturity begins to give place to a vicious circle of increasing impairment of function-in fact, to increasing age.

Some recent experiments hold out a hope that it may be possible to hold this progressive aging at bay. Steinach, in Vienna, by cutting the duct of the reproductive organ in the male, has been able in rats to cause an increase in the growth of the interstitial cells in this organ; a similar result— namely, an increase of the total amount of interstitial cells and of their secretion-can equally well be accomplished by grafting a whole organ from one animal to another. The effects, to judge from Steinach's pictures, are startling. Extremely senile rats, presenting a picture of old age cruelly like that to be seen in man, are converted in a few weeks into creatures apparently at the height of mature vigor.

The secretion of the interstitial cells apparently stimulates other ductless glands, such as the thyroid and pituitary, to renewed energy; and it stimu

lates the centers for the sexual instincts in the brain, whose activity, since all the parts of the brain are in communication, overflows and sets the rest of the mind more vigorously to work. After a time, considerable in proportion to the normal life of rats, a new old age descends upon the animal. It can be staved off by another graft, but each new attack of old age, if I may use the expression, is more acute, especially in its mental symptoms. Apparently the nerve-cells are progressively aging all the time, so that when the stimulus from the rest of the body begins to fail anew, they show a more sudden decay.

Operations have also been made on men, but it is obvious that considerable time and work will be needed before the new method can be regarded as established. It should not be forgotten that our knowledge of the ductless glands is in its infancy, and experiments such as these are of the greatest interest, since they open the door to new possibilities.

The speculative mind looks forward into the future and there sees great institutions for graft operations-human repair-shops. Men will have found methods for keeping organs alive outside the body, or they will be able to make grafts from tissuecultures. Thyroids, pituitaries, adrenals, pineals, interstitial tissue, and many other regulating organs now unknown, will be in their several places, and aging humanity will come in to have their bodily system reanimated as cars come in to a garage to be overhauled.

we can see at present, must sooner or later come to inevitable death.

However, since overpopulation is one of the great problems which the world has to face, that is hardly to be regretted, and we have only to turn to Gulliver's pages to be reminded of other disadvantages of deathlessness. What our present knowledge seems to prophesy as a possibility is a slight or moderate prolongation of life, at whose close the collapse of function we know as natural old age will come on us more rapidly and therefore more mercifully. We may hope that infectious diseases and diseases due to faulty diet will, with fuller knowledge, tend to disappear, and so Metchnikof's dream will come true, of a human race to whom age comes not prematurely, but in the fullness of time, and death arrives peacefully as the natural consummation of old age, not with the hatefulness of violence or disease. From the evidence which he collected of those rare men and women who die a really natural death from old age, Metchnikof thinks that a natural death is desired after life, as sleep is desired after a day's work, and believes that if the majority could live so as to die as nature, in his view, intended them, death would lose half its terrors, and life be thus released from half the weight of fear that now rests on it.

Meanwhile, with the rise of mind in evolution, changes have taken place in the nature of dominance. The brain is in contact with all other parts of the body by means of nerves; it becomes more and more complex; it receives more news of the outer world through improved sense-organs, and can deal better with that information as it develops mechanisms for memory or rea

It becomes the dominant part

of the organism. In man that part of the brain associated with mind is dominant over the rest; so that if we like we may say that mind dominates the human organism. Others have said it before. "Ideas rule the world" is an old proverb, though it is none the less important to have it formulated in a more general way. A healthy body is so much machinery; what use shall be made of it depends on the mind which dominates its working. To what extent this dominance may run is seen in every-day life in those who have some fixed belief or overruling passion. The miser's thoughts and actions are devoted to the amassing and hoarding of wealth; the lover's, to the object of his love; those of the neurasthenic who persists in believing that he is incapable of any achievement are paralyzed and brought to nothing.

Now, within the mind itself the same relation of dominance and subordination is at work, only in more complex fashion. It is impossible here to go into any detail of psychology, but we may, perhaps, be permitted to indicate one or two lines along which the concept is of value. In the first place, dominance without something to dominate is useless. In certain circumstances one can so cut a flatworm that nothing but a head will result from the piece; such structures are biological superfluities, doomed to speedy death. Now, recent work on psychology has shown that by a process of repression the higher centers of the human mind are capable of pushing anything unpleasant out of connection with themselves into a sort of mental limbo. Usually, it is the thoughts connected with definite instincts, such as the sexual instinct or the instinct of fear, that are thus

repressed. However, although repressed, they have their revenge; they continually attempt to reach the surface of consciousness again, and so ensues a conflict between two parts of the mind-a conflict which leads eventually to neurasthenia, depression, breakdown, or hysteria. In other men, perhaps the majority, conflict never arises, and the two tendencies, that of the simple instinct and that of the higher rational centers, exist side by side. Finally, however, there are those rare spirits to whom conflict comes, but is an opportunity for a new conciliation. They face the instinct which seems to threaten the higher things of the mind and make it their servant. They do not repress, but the fact that their higher centers are dominant only allows the subordinate system to develop to a certain degree and in a certain way. Finally, by the fact of association between different parts of the mind, it is possible for the higher centers to receive strength from their subordinate, and the lower instinct to be what the psychologists called sublimated, and its driving force thus turned into new and worthier channels.

The driving force of the mind springs always from emotions and instincts; thus the dominant parts of the mind must always be linked with emotion, with desire. What does this mean for education? At present education is too often thought of as a cramming of facts into the youthful mind. If this process, as it too often does, results in a distaste for knowledge, then one great aim of education has been missed. The aim of education should be to give those who are educated a desire for certain things—a desire to know things, a desire to act rightly, a desire for

beauty. If those desires are made dominant in the mind, most of the rest can be left to take care of itself.

Faith-cures, to use the widest possible term, provide another example. If a particular belief becomes a dominant part of the mind, the whole of the rest of the organism comes into relations with that belief. The most familiar case of unhealthy belief is seen in those patients suffering from depression who believe that they are good for nothing; if once the opposite belief can be made to live and become dominant in their mind, they will become healthy and useful human beings. A perusal of Baudouin's book, "Suggestion and Auto-suggestion," will furnish the reader with a number of remarkable cases where the general health, even in infectious disease, has been vastly improved under the influence of a dominant belief or faith.

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Finally, we may take an example where society rather than the individual man is affected. The actions of groups of men-societies, nations, federations are in the long run determined by the views held by the individual men and women that compose them. These views, dominant for the societies concerned, have as usual some emotion at their roots. The chief emotion concerned springs from man's gregarious instinct, and is his desire to be one of a large and, if possible, unanimous group. This may be intertwined with his views about any particular group-a tribe, a church, a nation, a class.

At the present time there are two chief types of such views in existence; there is nationalistic patriotism, and there is the class patriotism of certain