Читать книгу Preventable Diseases - Woods Hutchinson - Страница 7

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 Naturæ," 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 diarrhœa 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,[1] 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.