CHAPTER II

OUR LEGACY OF HEALTH: THE POWER OF HEREDITY IN THE PREVENTION OF DISEASE

The evil in things always bulks large in our imaginations. It is no mere coincidence that the earliest gods of a race are invariably demons. Our first conception of the great forces of nature is that they are our enemies. This misconception is not only natural, but even necessary on the sternest of physical bases. The old darky, Jim, in Huckleberry Finn, hit upon a profound and far-reaching truth when he replied in answer to Huck's question whether among all the signs and portents with which his mind was crammed—like black cats and seeing the moon over your left shoulder and "harnts"—some were not indications of good luck instead of all being of evil omen:—

"Mighty few—an' dey ain't no use to a body. What fur you want to know when good luck's a-comin'? Want to keep it off?"

It isn't the good, either in the forces of nature or in our fellows, that keeps us watchful, but the evil. Hence our proneness to declare in all ages that evil is stronger than good and that "all men are liars." One injury done us by storm, by sunstroke, by lightning-flash, will make a more lasting impression upon our memories than a thousand benefits conferred by these same forces. Besides, evil has to be sharply looked out for and guarded against. Well enough can be safely let alone.

The conviction is steadily growing, among both physicians and biologists, that this attitude has caused a serious, if not vital, misconception of the influence of that great conservative and preservative force of nature—heredity. We hear a great deal of hereditary disease, hereditary defect, hereditary insanity, but very little of hereditary powers of recovery, of inherited vigor, and the fact that ninety-nine and seven-tenths per cent of us are sane.

One instance of hereditary defect, of inherited degeneracy, fills us with horror and stirs us to move Heaven and earth to prevent another such. The inheritance of vigor, of healthfulness, and of sanity we placidly accept as a matter of course and bank upon it in our plans for the future, without so much as a thank you to the force that underlies it.

When once we clear away these inherited misconceptions and look the facts of the situation squarely in the face, we find that heredity is at least ten times as potent and as frequently concerned in the transmission and securing of health and vigor as of disease and weakness; that its influence on the perpetuation of bodily and mental defects has been enormously exaggerated and that there are exceedingly few hereditary diseases.

It is not necessary for our present purpose to enter into a discussion of the innumerable theories of that inevitable tendency of like to beget like, of child to resemble parent, which we call heredity. One reference, however, may be permitted to the controversy that has divided the scientific world: whether acquired characters, changes occurring during the lifetime of the individual, can be inherited. Disease is nine times out of ten an acquired character; hence, instead of the probabilities being that it would be inherited, the balance of evidence to date points in exactly the opposite direction. The burden of proof as to the inheritance of disease is absolutely upon those who believe in its possibility.

Another fundamental fact which renders the inheritance of disease upon a priori grounds improbable and upon practical grounds obviously difficult, is that characters or peculiarities, in order to be inherited certainly for more than a few generations, must be beneficial and helpful in the struggle. A moment's reflection will show this to be mathematically necessary, in that any family or race which tended to inherit defects and injurious characters would rapidly go down in the struggle for survival and become extinct. An inherited disease of any seriousness could not run for more than two or three generations in any family, simply for the reason that by the end of that time there would be no family left for it to run in. A slight defect or small peculiarity of undesirable character might run for a somewhat longer period, but even this would tend toward disappearance and elimination by the stern, selective influence of environment.

Naturally, this great conservative tendency of nature has, like all other influences, "the defects of its virtues," as the French say. It has no gifts of prophecy, and in the process of handing down to successive generations those mechanisms and powers which have been found useful in the long, stern struggle of the past, it will also hand down some which, by reason of changes in the environment, are not only no longer useful, but even injurious. As the new light of biology has been turned on the human body and its diseases, it has revealed so many of these "left-overs," or remnants in the body-machine—some of most dramatic interest—that they at first sight have done much to justify the popular belief in the malignant tendencies of heredity.

Yet, broadly considered, the overwhelming majority of them should really be regarded as honorable scars, memorials of ancient victories, monuments to difficulties overcome, significant and encouraging indications of what our body-machine is still capable of accomplishing in the way of further adjustment to conditions in the future. The really surprising thing is not their number, but the infrequency with which they give rise to serious trouble.

The human automobile is not only astonishingly well built, with all the improvements that hundreds of thousands of generations of experience have been able to suggest, but it is self-repairing, self-cleaning, and self-improving. It never lets itself get out of date. If only given an adequate supply of fuel and water and not driven too hard, it will stand an astonishing amount of knocking about in all kinds of weather, repairing itself and recharging its batteries every night, supplying its own oil, its own paint and polish, and even regulating its own changes of gear, according to the nature of the work it has to do. Simply as an endurance racer it is the toughest and longest-winded thing on earth and can run down and tire out every paw, pad, or hoof that strikes the ground—wolf, deer, horse, antelope, wild goat. This is only a sample of its toughness and resisting power all along the line.

These wide powers of self-support and adjustment overbalance a hundred times any little remnant defects in its machinery or gearing. Easily ninety-nine per cent of all our troubles through life are due to inevitable wear and tear, scarcity of food-fuel, of water, of rest, and external accidents—injuries and infectious diseases. Still, it occasionally happens that these little defects may furnish the point of least resistance at which external stresses and strains will cause the machine to break down. They are often the things which prevent us from living and "going to pieces all at once, all at once and nothing fust, just as bubbles do when they bust," like the immortal One-Hoss Shay. It is just as well that they should, for, of all deaths to die, the loneliest and the most to be dreaded is that by extreme old age.

These vestigia or remnants—instances of apparently hidebound conservatism on nature's part—are very much in the public eye at present, partly on account of their novelty and of their exceptional and extraordinary character. Easily first among these trouble-breeding remnants is that famous, or rather notorious, scrap of intestine, the appendix vermiformis, an obvious survival from that peaceful, ancestral period when we were more largely herbivorous in our diet and required a longer and more complicated food-tube, with larger side pouches in the course of it, to dissolve and absorb our food. Its present utility is just about that of a grain of sand in the eye. Yet, considering that it is present in every human being born into the world, the really astonishing thing is not the frequency with which it causes trouble, but the surprisingly small amount of actual damage that arises from it. Never yet in even the most appendicitis-ridden community has it been found responsible for more than one half of one per cent of the deaths.

Then there is that curious and by no means uncommon tendency for a loop of the intestine to escape from the abdominal cavity, which we call hernia. This is one of a fair-sized group of dangers clearly due to the assumption of the erect position and our incomplete adjustment thereto. In the quadrupedal position this necessary weak spot—a partial opening through the abdominal wall—was developed in that region which was highest from the point of view of gravity and least exposed to strain. In the bipedal position it becomes lowest and most exposed; hence the much greater frequency of hernia in the human species as compared with any of the animals.

Another fragment, of the impertinence of whose presence many of us have had painful proof, is the third or last molar, so absurdly misnamed the wisdom tooth. If there be any wisdom involved in its appearance it is of the sort characterized by William Allen White's delicious definition: "That type of ponderous folly of the middle-aged which we term 'mature judgment.'" The last is sometimes worst as well as best, and this belated remnant is not only the last to appear, but the first to disappear. In a considerable percentage of cases it is situated so far back in the jaw that there is no room for it to erupt properly, and it produces inflammatory disturbances and painful pressure upon the nerves of the face and the jaw.

Even when it does appear it is often imperfectly developed, has fewer cusps and fewer roots than the other molars, is imperfectly covered with enamel and badly calcified. In no small percentage of cases it does not meet its fellow of the jaw below and hence is almost useless for purposes of mastication. But it comes in every child born into the world, simply because at an earlier day, when our jaws were longer—to give our canine teeth the swing they needed as our chief weapons of defense—there was plenty of room for it in the jaw and it was of some service to the organism. If the Indiana State Legislature would only pass a law prohibiting the eruption of wisdom teeth in future, and enforce it, it would save a large amount of suffering, inconvenience, and discomfort, with little appreciable lack of efficiency!

In this list of admitted charges against heredity must also come the gall-bladder, that curious little pouch budded out from the bile ducts, which has so little known utility as compared with its possibility as a starting-point for inflammations, gall-stones, and cancer.

Then there is that disfiguring facial defect, hare-lip, due to a failure of the three parts of which our upper jaw is built to unite properly,—this triple construction of the jaw being an echo of ancestral fishlike and reptilian times when our jaws were built in five pieces to permit of wide distention in the act of swallowing our prey alive. All over the surface of the body are to be found innumerable little sebaceous glands originally intended to lubricate hairs, which have now atrophied and disappeared. These useless scraps, under various forms of irritation, both external and internal, become inflamed and give rise to pimples, acne, or "a bad complexion."

And so the list might be drawn out to most impressive length. But this length would be no indication of its real importance, inasmuch as the vast majority of entries upon it would come under the head of pathological curiosities, or conditions which were chiefly interesting on account of their rareness and unusual character. With the exception of the appendix, the gall-bladder, and hernia, these vestigial conditions may be practically disregarded as factors in the death-rate.

In the main, when the fullest possible study and recognition have been made of all the traces of experimentation and even of ancient failure that are to be found in this Twentieth Century body-machine of ours, the resulting impression is one of enormously increased respect for and confidence in the machine and its capabilities. While they are of great interest as indicating what the past history and experiences of the engine have been, and of highest value as enabling us to interpret and even anticipate certain weak spots in its construction and joints in its armor, their most striking influence is in the direction of emphasizing the enormous elasticity and resourcefulness of the creature.

Not only has it met and survived all these difficulties, but it is continuing the selfsame processes to-day. So far as we are able to judge, it is as young and as adaptable as it ever was, and just as ready to "with a frolic welcome greet the thunder and the sunshine" as it ever was in the dawn of history.

These ancestral and experimental flaws, even when unrecognized and unguarded against, have probably not at any time been responsible for more than one or two per cent of the body's breakdowns; while, on the other hand, every process with which it fights disease, every trick of strategy which it uses against invading organisms, every step in the process of repair after wounds or injury, is a trick which it has learned in its million-year battle with its surroundings.

Take such a simple thing as the mere apparently blind habit possessed by the blood of coagulating as soon as it comes in contact with the edges of a cut or torn blood-vessel, and think what an enormous safeguard this has been and is against the possibility of death by hemorrhage. So well is it developed and so rapidly does it act that it is practically impossible to bleed some animals to death by cutting across any vessel smaller than one of the great aortic trunks. The rapidity and toughness of the clotting, combined with the other ancestral tricks of lowering the blood pressure and weakening down the heart, are so immensely effective that a slash across the great artery of the thigh in the groin of a dog will be closed completely before he can bleed to death. So delicate and so purposeful is this adjustment that the blood will continue as fluid as milk for ten, twenty, forty, eighty years—as long as it remains in contact with healthy blood-vessels. But the instant it is brought in contact with a broken or wounded piece of a vessel-wall, that instant it will begin to clot. So inevitable is this result that it gives rise to some of the sudden forms of death by bloodclot in the brain or lung (apoplexy, "stroke"), the clot having formed upon the roughened inner surface of the heart or of one of the blood-vessels and then floated into the brain or lung.

Then take that matchless and ingenious process of the healing of wounds, whose wondrousness increases with every step that we take into the deeper details of its study. First, the quick outpouring and clotting of the blood after enough has escaped to wash most poisonous or offending substances out of the wound. This living, surgical cement, elastic, self-moulding, soothing, not only plugs the cut or torn mouths of the blood-vessels, but fills the gap of the wound level with the surface. Here, by contact with the air and in combination with the hairs of the animal it forms a tough, firm, protective coating or scab, completely shutting out cold, heat, irritants, or infectious germs.

Into the wedge-shaped, elastic clot which now fills the wound from bottom to top like jelly in a mould, the leucocytes or white blood-cells promptly migrate and convert it into a mesh of living cells. They are merely the cavalry and skirmishers of the repair brigade and are quickly followed by the heavy infantry of the line in the shape of cells born of the injured tissues on either side of the wound. These join hands across the gap, the engineer corps and the commissariat department move up promptly to their support in the form of little vein-construction switches, which bud out from the wounded blood-vessels. The clot is transformed into what we term granulation tissue and begins to organize. A few days later this granulation tissue begins to contract and pull the lips of the wound together. If the gap has not been too wide the wound will be completely closed, its lips and deeper parts drawn together in nearly perfect line, separated only by a thin scar on the surface with a vertical keel of scar tissue descending from it. If the lips cannot be drawn together and there be no surgical skill at hand to assist them with stitches or bandages, then the gap will be filled up by the fibrous transformation of this granulation tissue and a thick, heavy scar result. Meanwhile, the skin-cells of the surface have not been idle, but are budding out on either side of the healing wound, pushing a little line of colonists forward across the raw surface. In longer or shorter time, according to the width of the gap, these two lines meet, and the site of our wound or the scar that it has left is perfectly coated over with a layer of healthy skin. This drama has occurred so many score of times in every one of us that custom has blinded our eyes to its ingenious perfection, but it took a million years to bring it to its present finish.

It may be a healthy corrective to our overweening conceit to remind ourselves that, remarkable and valuable as it is, it is a mere infant in arms compared to the superb powers of replacement and repair possessed by our more remote ancestors. Most invertebrates and many of the lowest two classes of backboned animals, the fishes and the amphibians, cannot merely stop up a rent, but renew an entire limb, fin,—yes, even eye or head. Cut an earthworm in two and the rear half will grow a new head and the front half a new tail. It may even be cut in four or five segments, each of which will proceed to form a head at one end and a tail at the other. The lobster can regrow a complete gill and any number of claws or an eye. A salamander will reproduce a foot and part of a limb. Take out the crystalline lens in the eye of a salamander and the edge of the iris, or colored part of the eye, will grow another lens. Take out both the lens and the iris and the choroid coat of the eye will reproduce both.

We are in the A, B, C class in powers of repair by comparison with the angleworm, the lobster, or the salamander. Yet we are not without gruesome echoes of this lost power of regeneration in that our whole brood of tumors, including the deadly cancer and sarcoma, are due to a strange resumption, on the part of some little knot of our body-cells, of the power of reproducing themselves or the organ in which they are situated, without any regard to the welfare of the rest of the body. Cancer is, in one sense, a throwing off of the allegiance to the body-state and a resumption of amphibian powers of independent growth on the part of certain groups of our body-cells—literally, a "rebellion of the cells."

These are but a handful of scores of instances that could be adduced, showing that the majority of the processes upon which we rely in combating disease and preserving life are the result of the hereditary experiences of our cells. Intelligent physicians are receding completely from that curiously warped and jaundiced view which led us to regard heredity chiefly as a factor in the production of disease. It was, perhaps, natural enough, since it was inevitably only its injurious, or, so to speak, malicious, effects which were brought to our attention to be corrected. But, just as in the growth of our ethnic religions it is Evil that is worshiped first as strongest and most aggressive, and the recognition of the greater power of good comes only at a later stage, so it has been in pathology.

Not only do we regard heredity as a comparatively small and steadily receding factor in the production of disease, but we fully and frankly recognize it as the strongest and most important single force in its prevention. All our processes of repair, all the reactions of the body against the attack of accident or of disease, are hereditary endowments, worked out with infinite pains and labor through tens of thousands of generations. The utmost that we can do with our drugs and remedies is to appeal to and rouse into action the great healing power of nature, the classic "Vis medicatrix Naturae," an incarnation of our past experiences handed down by heredity. Enormously valuable and important as are the services to human welfare, health, and happiness which can be rendered by the destruction of the living external causes of disease and the prevention of contagion, our most permanent and substantial victories are won by appealing to and increasing this long-descended and hard-won power of individual resistance.

"But," says some one at once, "I thought there were a large number of hereditary diseases." Fifty years ago there were a score of such, twenty years ago the score had sunk to five or six. Now there is scarcely one left. There is no known disease which is directly inherited as such. There is scarcely even a disease in which we now regard heredity as playing a dominant or controlling part. Among the few diseases in which there is serious dispute as to this are tuberculosis, insanity, epilepsy, and cancer.

Then there are diseases which for a long time puzzled us as to the possibility of their inheritance, but which have now resolved themselves clearly into instances of the fact that a mother who happens to contract an acute infectious disease of any sort may communicate that disease to the unborn child. If this occurs at an early stage of development the child will naturally be promptly killed. In fact, this is the almost invariable result in smallpox and yellow fever. If, on the other hand, development be further advanced or the infection be of a milder character, like scarlet fever or syphilis, the child may be born suffering with the disease or with the virus in its blood, which will cause the disease to develop within a few days after birth. This, however, is clearly not inheritance at all, but direct infection. We no longer use the term hereditary syphilis but have substituted for it the word congenital, which simply means that a child is born with the disease.

There is no such thing as this disease extending "unto the third and fourth generation," like the wrath of Jehovah. One fact must, of course, be remembered, which has probably proved a source of confusion in the popular mind, and that is its extraordinary "long-windedness." It takes not merely two or three weeks or months to develop its complete drama, but anywhere from three to thirty years, so that it is possible for a child to be born with the taint in its blood and yet not exhibit to the non-expert eye any sign of the disease until its eighth, twelfth, or even fifteenth year.

The case of tuberculosis is almost equally clear-cut. In all the thousands of post-mortem examinations which have been held upon newborn children and upon mothers dying in or shortly after childbirth, the number of instances of the actual transference of the bacilli of tuberculosis from mother to child could be counted upon the fingers of two hands. It is one of the rarest of pathologic curiosities and, for practical purposes, may be entirely disregarded. When tuberculosis appears in several members of a family, in eight cases out of ten it is due to direct infection from parents or older children. This is strikingly brought out in the admirable work done by the Associated Dispensaries for Tuberculosis of the Charity Organization Society of New York.

One of the first steps in advance which they took was to establish in connection with every clinic for tuberculosis an attendant nurse, whose duty it was to visit the patients at their homes and advise and instruct them as to improvements in their methods of living, ventilation, food, and the prevention of infection.

It was not long before these intelligent women began to bring back reports of other cases in the same family. Now the procedure is regularly adopted, whenever a case presents itself, of rounding up the remainder of the family group for examination, with the astounding result that where a mother or father is tuberculous, from twenty to sixty per cent of the children will be found to be suffering from some form of the infection. Instances of three infected children out of five living in the same room with a tuberculous mother are actually on record.

No one can practice long in any of our great climatic health resorts for tuberculosis, like Colorado or the Pacific Slope, without coming across scores of painful and distressing instances of children of tuberculous parents dying suddenly in convulsions from tuberculous meningitis, or by a wasting diarrh[oe]a from tuberculosis of the bowels, or from a violent attack of distention of the bowels due to tuberculous peritonitis. The favorite breeding-place of the tubercle bacillus is unfortunately in the home.

On the other hand, while the vast majority of cases of so-called hereditary tuberculosis are due to direct infection, and may be prevented by proper disposal of the sputum and other methods for avoiding contagion, there is probably a hereditary element in the spread of tuberculosis to this degree: that, inasmuch as all of us have been exposed to the attack and invasion of the tubercle bacillus, not merely scores, but hundreds of times, and have been able to resist or throw off that attack without apparent injury, the development of an invasion of the tubercle bacillus sufficiently extensive to endanger life is, in nine cases out of ten, in itself a proof of lowered resisting power on the part of the patient. This may be, and often is, only temporary, due to overwork, underfeeding, overconfinement, or that form of gradual suffocation which we politely term inadequate ventilation.

In a certain percentage of cases, however, it is due to a chronic lack of vigor and vitality; a lowering of the whole systemic tone, which may have existed from birth. In that case it is hardly to be expected that such an individual, becoming a parent, will be able to transmit to his or her offspring more vigor than he originally possessed. It is therefore probable that the children of a considerable percentage of tuberculous parents would not possess the same degree of resisting power against tuberculosis, or any other infection, as the average individual.

It is doubtful whether this factor of inherited lowered resistance plays any very important part in the propagation of tuberculosis, partly because it is comparatively seldom that consumptive marries consumptive, and such tendencies to lowered vigor and vitality as may be transmitted by one parent will be neutralized by the other; partly also because, by the superb and beneficent logic of nature, the pedigree of any disease is of the most mushroom and insignificant length, while the pedigree of health stretches back to the very dawn of time. In the struggle for dominance which takes place between the germ cells of the father and those of the mother, the chances are at least ten to one in favor of the old ancestral traits of vigor, of resisting power, and of survival. How deeply this idea is implanted in the convictions of the scientific world, the bitterly and widely debated biologic question whether acquired characters or peculiarities can under any circumstances be inherited clearly shows. Victory for the present rests with those who deny the possibility of such inheritance, and disease is emphatically an acquired character.

Truth here, as everywhere, probably lies between the extremes, and both biologists and the students of disease have arrived at practically the same working compromise, namely, that while no gross defect, such as a mutilation, nor definite disease factor, such as a germ, nor even a cancer, can possibly be inherited, yet, inasmuch as the two cells, which by their development form the new individual, are nourished by the blood of the maternal body, influences which affect the nutritiousness or healthfulness of that blood may unfavorably influence the development of the offspring.

Disease cannot be inherited any more than a mutilating defect, but the results of both, in so far as they affect the nutrition of the offspring in the process of formation, may be transmitted, though to a very much smaller extent than we formerly believed. In the case of tuberculosis, if the mother, during the months that she is building up the body and framework of a child, is in a state of reduced or lowered nutrition on account of consumption or any other disease, or has her tissues saturated with the toxins of this disease, it is hardly to be expected that the development of the child will proceed with the same perfection as it would under perfectly normal maternal surroundings.

However, even this influence is comparatively small; for one of the most marvelous things in nature is the perfection of the barrier which she has erected between the child before birth and any injurious conditions which may occur in the body of the mother. Here preference, so to speak, is given to the coming life, and whenever there is a contest for an adequate supply of nutrition, as, for instance, in cases of underfeeding or of famine, it is the mother who will suffer in her nutrition rather than the child. The unborn child, biologically considered, feeds upon the best she has to offer, rejecting all that is inferior, doing nothing and giving nothing in return.

How perfectly the coming generation is protected under the most unfavorable circumstances we have been given a striking object-lesson in one family of the lower animals. In the effective crusade against tuberculosis in dairy cattle waged by the sanitary authorities in Denmark, it was early discovered that the greatest practical obstacle to the extermination of tuberculosis in cattle was the enormous financial sacrifice involved in killing all animals infected. The disease was at that time particularly rife among the high-bred Jersey, Holstein, and other milking breeds. It was determined as a working compromise to test the truth of the modern belief that tuberculosis was transmitted only by direct infection, by permitting the more valuable cows to be saved alive for breeding purposes. They were isolated from the rest of the herd and given the best of care and feeding. The moment that their calves were born they were removed from them altogether and brought up on the milk of perfectly healthy cows. The milk of the infected cows was either destroyed or sterilized and used for feeding pigs.

The results were brilliantly successful. Scarcely one of the calves thus isolated developed tuberculosis in spite of their highly infected ancestry. And not only were they not inferior in vigor and perfection of type to the remainder of their breed, but some of them have since become prize-winners. The additional care and more abundant feeding that they received more than compensated for any problematic defect in their heredity.

As to the heredity of cancer, all that can be said is that the burden of proof rests upon those who assert it. It is really curious how widespread the belief is that cancer "runs in families," and how exceedingly slender is the basis of evidence for such a belief. There are so many things that we do not know about cancer that any positive statement of any kind would be unbecoming. It would be absurd to declare that a disease, of which the cause is still unknown, either is or is not inherited. And this is our position in regard to cancer. An overwhelming majority of the evidence so far indicates that it is not a parasite; if it were, of course, we could say positively that it is not inherited. Although we are getting a discouraging degree of familiarity with the process and clearly recognize that it consists chiefly in the sudden revolt or rebellion of some group of cells, a tendency which quite conceivably might be transmitted to future generations, yet it is highly improbable, on both biological and pathological grounds, that such is the case. If this rebellious tendency were transmitted we should at least have the right to expect that it would appear in the cells of the same organ or region of the body. It is a singular fact that in all the hundreds of cases in which cancer has appeared in the child of a cancerous parent it has almost invariably appeared in some different organ from that affected in the parent.

For instance, cancer of the lip in the father may be followed by cancer of the liver in the son or daughter, while cancer of the breast in the mother will be followed by cancer of the lip in a son. Further than this, the percentage of instances in which cancer appears in more than one member of a family is decidedly small, considering the frequency of the disease.

I took occasion to look into the matter carefully from a statistical point of view some ten or twelve years ago, and out of a collection of some fifty thousand cases of cancer less than six per cent were found to give any history of cancer in the family. And this, of course, simply means that some one of the relatives of the patient had at one time developed the disease.

In fact, the consensus of intelligent expert opinion upon the subject of heredity of cancer is, that though it may occur, we have comparatively little proof of the fact; that the percentage of cases in which there is cancer in the family is but little larger than might be expected on the doctrine of probabilities from the average distribution. Though possibly the offspring of a cancerous individual may display a slightly greater tendency toward the development of that strange, curious process of "autonomy" than the offspring of the average individual, this tendency is so small and occurs so infrequently as to be a factor of small practical importance in the propagation and spread of the disease.

In insanity and epilepsy we have probably the last refuge and almost only valid instance of the old belief in the remorseless heredity of disease. But even here the part played by heredity is probably only a fraction of that which it is popularly, and even professionally, believed to play. It is, of course, obvious that diseases which tend quickly to destroy the life of the patient, especially those which kill or seriously cripple him before he has reached the age of reproduction, or prevent his long surviving that epoch, will not, for mechanical reasons, become hereditary. The Black Death, or the cholera, for instance, could not "run in a family." Supposing that children were born with a special susceptibility to this disease, there would obviously soon be no family left.

The same is true in a lesser degree of milder or more chronic diseases. The family which was hereditarily predisposed to scarlet fever, measles, smallpox, or tuberculosis would not last long, and in fact the whole progress of civilization has been a continuous process of the weeding out of those who were most susceptible and the survival of those who were least so.

But when we come to deal with certain conditions, fortunately rare, such as functional disturbances of the nervous system, which neither seriously unfit their possessor for the struggle of life nor prevent him from reproducing his kind, then it becomes possible that a tendency to such disease may be transmitted through several successive generations.

Such is the case with insanity, with epilepsy, with hemophilia, or "bleeders," and with certain rare and curious disturbances of the nervous system, such as the hereditary ataxias and "tics" of various sorts. However, even here the only conditions on which these diseases can continue to run in a family for more than one or two generations is either that they shall be mild in form or that only a comparatively small percentage of the total family shall be affected by them. If, for instance, two-thirds, one-half, or even a third of the descendants of a mentally unsound individual were to become insane, it would only need a few generations for that family to be crushed to the wall.

While the descendants of insane persons are distinctly more liable to become insane than the rest of the community, yet, on account of their fewness, this tendency probably does not account for more than a small fraction of the total insanity. We should, by all means, prevent the marriage of the insane and discourage that of their children, and the development of any well-defined form of insanity should act at once, ipso facto, as a ground and cause of divorce.

But the consoling fact remains that even of such children, providing, of course, as usually happens, that the other parent—husband or wife—is sound and sane, not more than ten or fifteen per cent would probably become insane. In other words, insanity is acquired and the result of individual stress and strain at least five times as frequently as it is inherited. We have absolutely no rational or statistical basis for gloomy predictions that, at present rates, within a couple of centuries more, we shall all be shut up in asylums with nobody left to support us and pay the taxes. The apparent increase of insanity of recent decades is probably only "on paper," due to better registration.

To put it very roughly, probably ninety-eight per cent of us are so born, thanks to heredity, that the possibility of our becoming insane, even under the severest stress, is almost infinitesimal. Of the two per cent born with this taint, this possible tendency to mental unbalance, only about one-tenth now become completely insane, and this percentage might be greatly diminished by general sanitary improvements. Our alienists now claim that, by checking the reproduction of the obviously unstable, and careful hygienic treatment and training of the predisposed two per cent, insanity is almost as preventable as tuberculosis.

In fine, from all the broad field of pathology, the mists of tradition which have dimmed the fair name and reputation of heredity are slowly but surely lifting, until we now behold it, not as our worst enemy, but as our best friend in the prevention of disease and the upbuilding of the race.