# Popular Science Monthly/Volume 15/August 1879/Removal of Inherited Tendencies to Disease

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THE
POPULAR SCIENCE
MONTHLY.
AUGUST, 1879.
* REMOVAL OF INHERITED TENDENCIES TO DISEASE.
By J. R. BLACK, M. D.
A LIMITED collection of statistics and the observation of physicians concur in showing that about two thirds of our people inherit a tendency to some disease, or to a defective vitality in some organ of the body. In very many instances the overshadowing heritage is toward an untimely death, while in others it is simply toward some chronic insufficiency which embitters many a year of life.
The number who think themselves doomed to a premature death by some innate blood defect is very great. At this moment hundreds of thousands are ready to interpret every sign of thoracic derangement as the harbinger to the development of that dreaded inheritance—pulmonary consumption. Taking into consideration that, according to the last census, about seventy thousand throughout our land are swept into the grave each year by this disease, cause for alarm seems sufficiently ample. The aggregate of foreboding, of suffering, and of heart-wringing grief at untimely separations through this scourge alone, would be terrible to contemplate were we capable of apprehending it as a whole. Add to this the heritage in numerous instances of a tendency to rheumatism, to gout, to epilepsy, to insanity, to cancel, and the host of those distressed in mind or in body attains a painful magnitude. A subordinate and large group of heritages are yet to be added. Every year thousands are brought into the world with digestive organs so imperfect that the slightest indiscretion precipitates misery; others are tormented for life by the development of an inherited tendency to migraine, to neuralgia, or to asthma; and not a few through the same agency lose their sight or their hearing during the prime of life.
​To go on with a bare enumeration of the organic defects handed down from parent to child would occupy many pages. Enough has been said to convey some idea of the magnitude of the evil. There is no cause of grief, of misery and suffering that will hear comparison with it. Even that of war is a mercy compared with the torments of disease. The seventy thousand annually slain by one disease, consumption, involves an amount of suffering which no battle-field can equal. In the latter death is usually sudden, and therefore almost painless, while death by consumption implies months of torture by the destruction of lung tissue inch by inch.
In an age distinguished for progress and philanthropy, that such a gigantic evil has received scarcely any attention is worthy of remark. In large part is this doubtless due to the prevailing opinion that the development of inherited tendencies to disease is unavoidable—a visitation upon children for the sins of the fathers, not to be averted. Even among medical men is there a prevailing skepticism as to the renovation of defective blood. Yet it will be admitted by the candid among them that this doubt is not grounded on a careful study of the subject, but on some desultory observations, and on some remarks to be met with here and there in medical literature. In palliation this may be said, that as a rule physicians are far more intent in discovering the best means of curing than of averting disease, well knowing that the latter is a thankless and little honored pursuit, while the former brings large returns of gratitude and reward.
If in our forty millions of people some twenty-six million inherit some constitutional defect, the question is of deep and wide interest whether such imperfection can be erased, and, if so, by what means. The interests involved are: a nearer extension of life to its normal limits, greater freedom from disease and deformity; a diminution in the necessity for ever-growing asylums for the helplessly imperfect and diseased; an increase of the ratio of able-bodied men for the defense of the state in time of need; a lessened necessity for the consumption of drugs and the support of forty thousand physicians; and an increase and perpetuation of the blood which has been our chief glory as a nation.
The nearer the approach to physical perfection, the less likely will be the occurrence of derangement and disease from slight causes, such as atmospheric vicissitudes, and the greater the chances that the termination of life will be natural, or from the harmonious, progressive, and painless decay of the body as a whole. Death by disease through one organ is abnormal, violent, and torturing; there should be no weak points in the citadel of life. Men with excellent physical organizations do not need to be ever on the watch for the preservation of their health. They possess that buoyancy of life which carries them safely over all the minor influences inimical to healthy action. All that is required of them for the preservation of such a vital excellence is, that ​unfavorable influences shall not be too intense, or suffered to act upon them for any great length of time. On the other hand, those defectively organized can not overstep the bounds of the most watchful prudence without incurring suffering. Only by the most minute and accurate knowledge of hygiene, and unswerving attention to its requirements, are they enabled to avoid pain, disease, and an untimely end.
The genius of our civilization in its physiological aspect is to make spendthrifts of us all of our vital riches. It includes no such aim as race improvement. True, some youthful culture of the head and heart is supposed to reach after that object. But it does not. It looks only to immediate success in social distinctions, or to winning in competitive struggles, not to the more remote objects of our improvement as a race. Indeed, the instances in which physical degeneration, by the prevailing injudicious and highly prized head-culture, is not thereby begun, are altogether exceptional. Compare the highly educated son with his father, and a perceptible diminution in the grade of constitutional stamina is nearly always manifest. Continue the process for a generation or two, and a progressive deterioration will ensue until there are only sickly boys to grow up into invalided manhood.
Very few ever think of, and yet fewer ever seek after, the accumulation of vital riches. Only when brought to suffering by poverty of this kind is the mind aroused to any interest in the subject. Prior to the inception of disease, a thoughtless squandering of vital reserve is what our social practices systematically encourage; and when as a consequence corporeal structure is inharmoniously developed, when debility, disease, and untimely death ensue, these are not regarded as the evidences of a fatal flaw in the existing system of civilization, but as matters of prevision which alone concern Providence and the doctors. The constitutional vigor, thus so blindly spent, renders frequent demands upon the highest resources of the healing art urgently necessary. And it must be confessed that in prolonging the life of defective blood there are displayed a skill and care never before equaled. During the more primitive phases of civilization, those of weak and defective blood were more liable to be swept into an untimely grave than they are to-day. Now, all such are skillfully nursed up to the fertile period, to the multiplication and perpetuation of their kind. The profound study, the active sympathy, and systematic charity bestowed upon the wrecks of our race for their cure and preservation, when compared with the prevailing indifference as to the means of preventing the steady increase of such helpless unfortunates, is far from flattering to our foresight in economy and beneficent work. Vast infirmaries, hospitals, and asylums dot the land to shelter and cure the ever-increasing ratio who become pitifully and hopelessly bankrupt in vital condition; yet there is no money, no labor, light, or system brought to bear to hinder this downward career, but very much of all—thoughtlessly we will allow—to aid in its increase and perpetuation. ​Optimists assure us that even if insanity, idiocy, deaf-mutism, blindness, and intractable disease and deformity be upon the increase, the evil is not unmingled with good, as it at once serves the twofold purpose of illustrating and exercising the benevolence of the age.
The only rational interpretation that can be put upon the manifestations of defective blood is, that they are the prodroma of its extinction. If the genetic conditions are continuously applied, such will be, as familiar experience often illustrates, the ultimate result; the salient points of the process being, a large infant mortality, death before reproduction, and infertility. On the theory of Dr. N. Allen, that increase of population is mainly governed by the law of approximation to perfection in bodily structure and harmony of function, the postulate can be easily proved that, as a people, we are gradually but surely degenerating. Dr. Toner, the compiler of vital statistics at the national capital, has found that "there is undoubted evidence of a gradual decline in the proportion of children under fifteen to the number of women between fifteen and fifty years of age throughout our country."
The vital statistics of Rhode Island have been carefully and intelligently collected for many years by Dr. Snow, who states that there has been a gradual decline in the birth-rate among those of American parentage for the last twenty years. The same is true of Massachusetts, and, in fact, of New England; the birth-rate being actually lower than in any country of Europe, France alone excepted.
The causes of race degeneration are usually very complex; some pertaining to environment, others to a faulty personal hygiene. Through heredity all the evil effects are accumulated and perpetuated. But fortunately there is a principle in life which tends to antagonize and obliterate the destructive tendency of these innate defects upon life. If nothing of the kind existed—if there were no opposing force—the failure of physiological action would be rapid, uniform, and progressive, until morbid energy gained its fatal mastery over that which tends to hold organic structure in a cycle of harmonious changes.
What is known as reversion, and termed by Darwin "the great principle of inheritance," furnishes the clearest conception of this opposing energy. Of its essential cause nothing is known, but as to its steady operation there is indubitable evidence. In two well-defined conditions of organic life, its steady influence may be observed: in processes that are normal, and in those that are abnormal. The influence of reversion in the perpetuity of normal characters is fully recognized, but the same can not be said of its true relation to those that are abnormal. Writers who have treated upon this point apparently consider the principle as one which tends to restore a lost character without regard to its nature, or, in other terms, that a quality ill suited for the continuance of life, and which has disappeared for one or more generations, is quite as likely to reappear as one well suited. This ​conclusion appears to be sustained by ordinary observation, although the conditions which bring about the reappearance of abnormities may be quite different from those which tend to restore lost normalities. The more attentively, however, the subject is considered, the more apparent does it become that the differences in the two cases are far greater than has been supposed, extending back to the antecedents, to the nature, duration, and outcome of the process.
One of the constants of reproduction is more or less variability in the offspring, and this may be healthy or physiological, or it may be morbid. When of the former, it is in no way incompatible with life, and may prove permanent to the blood; but more commonly it is supplanted by older characters, which may have disappeared for one or more generations. The nature of the prepotent tendency to reversion seems to be grounded upon a single antecedent, that of prolonged 'transmission. As a rule, it happens that the longer this has occurred the more deeply fixed does any character become, and hence the more likely, when caused to vanish by modifying conditions, to reappear through reproduction.
Exceptionally, it is true, modifying circumstances seem to have so ripened in the organism for a variation that a change of structure and function is uninterruptedly transmitted.
That the prolonged existence of characteristics should tend to fix them strongly upon the blood is in entire harmony with familiar experience. For example, there is nothing permanent in the minute diversities among the individuals of a race, but the general type has long existed, and is preserved for generation after generation with unbroken fidelity. No competent observers think it possible to raise the intellectual grasp of a stupid family or race to the highest average by the culture of one or two generations. Time and continuity of influence are indispensable to the fixing and maintenance of intellectual excellence. To the influence of these elementary conditions is no doubt due the wide disparity between the transmission of instinctive and intellectual skill. In the latter process the thoughts and actions are so numerous and diversified, that the continuance of any one is necessarily short and evanescent, while in the former they are few and always in the same narrow channel. In this way the instinctive brain-impressions of the animal are grooved or deeply stamped into its structure, making their acts a necessary resultant; while those of intelligence leave but a shallow impress, so that skillful execution can only be attained by individual training and practice.
When the variation that springs from the ripe influence of modifying conditions is of a normal character, it has no inherent quality which renders indefinite perpetuation impossible. Let its favoring conditions be continuously applied, and it may become permanent to the blood, and thus acquire the prepotency of reversion. Quite otherwise is the result with variations of an abnormal or morbid character. ​Their presence implies an unceasing and more or less violent struggle between the tendency to an untimely death and the natural term of life. The prolonged existence of such variations, especially when they affect the more important organs, is scarcely possible; progressing in acute attacks, or through descent, either toward reversion or toward lineage extinction. Indeed, if abnormities were in their nature as permanent and compatible with the life of the blood as normalities, they would cease to be such, and all distinctions between them would vanish. Some deviations, however, from ordinary development, such as polydactylism, can not be considered morbid, and are in no way incompatible with the continuance of life.
Organic variability is mainly, if not entirely, an effect of changes in condition. The increased use or disuse of any part, a change from one climate to another, and of the quantity or quality of food, have long been noticed to be specially influential. The various species of domesticated plants and animals are far more variable than the same when wild, a difference readily accounted for by the fact that the latter are far less migrant; their nutriment and the culture of parts undergo little if any change in great lapses of time. Some variations, like that of the loss of wool which our sheep undergo when placed within the tropics, are apparently grounded upon adaptation to relation, others upon adaptation to use, and others are dependent on methodical selection.
One and all of these diverging tendencies are opposed by a single conservative principle, that of reversion. The tendency of animals long domesticated when they become feral to revert to the pristine type might also be supposed to arise from adaptation to relation. But the tendency is often seen when there has been no apparent change in the conditions, as in the many and familiar instances of atavism; and more decisively, by the crossing of species. The experiment of the Earl of Powis is one example of the many which evince the marked tendency to reversion through the crossing of blood. He had some domesticated hump-backed cattle crossed by the wild species from India, with the result, not of producing a medium grade of characteristics, but of a marked reversion to the ancient. Here, adaptation to relation can not be regarded as effective; only through the indelibility of types by prolonged transmission is such a prepotency explicable.
The principle of reversion is the touchstone of the fitness for survival of blood variations normal in character. If they withstand for indefinite generations the tendency to be supplanted by older and more deeply fixed characters, their fitness is proved, and at the same time they acquire prepotency for strong maintenance against fresh deviations. The principle is therefore eminently conservative, and not a mere blind tendency of the organic processes. Unlike the coarse and obtrusive struggle for existence between independent organisms, it is ​a molecular contest of refined organic principles, not visible or audible in its details, but in general scope and outcome as manifest and beneficent in its operation as its more familiar congener.
Though the conservative influence of reversion is quite apparent in variations of a normal kind, it is far more so in those that are morbid or abnormal. Here the struggle between the variation and the tendency to the maintenance of durable types is usually so sudden, violent, and quickly decisive, that it is vividly realized. Upon the tendency of deranged actions to revert into the old channels of health does the therapeutist ground all hopes of his ability to assist in the process. When that is manifestly impotent, no means he can bring to bear will arrest the speedy termination of life. Cullen attributed the tendency in disease to reversion or recovery—for they are identical—to a vis medicatrix naturæ. The conception is little more than a barren ideality, and does not accord with the fundamental truth that of causes we can know nothing only of the relations of phenomena to each other. The vis medicatrix naturæ has not been shown to have any antecedent; it is simply a name for a supposed entity, apparently latent until disease appears. According to the views here adduced, it is resolvable into the general principle manifest in all kinds of organic life: the strong tendency to the maintenance of characters which a great lapse of time has proved are the most fit. If this generalization be truly grounded, it adds another to some more notable in which modes of action once considered as produced by independent forces were really transmutations of one.
The frequency with which the principle of reversion gains the mastery in attacks of acute disease is one of the most striking phases of vital action. Form and function are seen to revert to their old types and channels of action as if they had never nearly perished. The struggle against abnormal variations is violent, continuous, but not prolonged. Either the abnormity or reversion quickly gains the mastery; in the former case the end is dissolution, in the latter health. In some instances the morbid variation is slow, insidious, or mild in nature; the struggle is then less conspicuous, 'more prolonged, but never suspended. When the abnormal variation gains the mastery, it does not survive or establish its fitness by indefinite perpetuation, and so acquire the prepotency of reversion. Untimely death is the signal and sequel of its mastery, and until this or reversion gains supremacy no peace or continued harmony of action is possible. True, blood affected by a morbid variation chronic in its nature often displays sluggish and varying fortunes in its struggle with reversion for mastery; favoring conditions now giving reversion the ascendancy, then unfavorable conditions impart a renewed energy to the unhealthy tendency. Yet a marked lineage struggle for survival is rarely very extended—the compass of a single life's observation not unfrequently witnessing its close.
​Morbid variations of structure and function present three leading phases of action, the acute, chronic, and diathetic. The primary causes of each are the same, a faulty personal hygiene and an unfavorable environment, but a derivative cause very generally predominates in the heritage of a defect or taint in the blood. In acute variations the struggle between the tendency to death and the tendency to reversion is usually short and severe, but decisive. The contending forces are often so nearly equal that a very little will turn the scale one way or the other. Chronic variations only differ from acute in this, that they are milder, or are more tolerable to the vital autonomy. The same inherent principle struggles in each for the restoration of health, although the process is not so impressively realized in the chronic as in the acute form, by a rapid and well-defined course. What dissimilarity there is in the two series of actions is wholly one of time and degree, not of nature, the struggle between the tendency to health and the tendency to disease presenting almost every conceivable phase of activity, and lasting from a day to months or even years.
As no one can say precisely when acute diseases end and chronic begin, the distinction being arbitrary and accepted for convenience, no more can any one say exactly when a slow disease is changed into a diathesis. In fact, there are no sound reasons in support of the opinion that such a change ever sharply occurs; but there are in support of this, that a slow disorder is often gradually toned down until it merges into a diathesis, when it is then known as a predisposition. During the gradual disappearance of a slow disease one of untutored and gross perceptions may decide recovery to be complete, while the acute adept may be able to discern the manifestations of the disorder subsequently for months. Indeed, there is scarcely any room for doubt that, if our senses were far more acute, a diathesis or tendency to some special disease would be disclosed in definite signs of imperfection, or of disorder. A diathesis is often seen gradually merging into development, and development into a diathesis, and the frequency with which this is seen to recur in the same person gives tone to the conclusion that the letter state is only a very mild or occult phase of the former. Any ordinary observer, with a predisposition to some disorder, is aware that very slight exciting causes usually serve sufficiently to increase the imperceptible imperfection as to bring it within the cognizance of the senses. But there is yet more indubitable evidence that a series of morbid changes may be going on in the body of which no cognizance can be taken. During the incubative stages of scarlet fever, measles, small-pox, and syphilis, the contagium of each has a definite period of maturative action before the signs of disease are in any way apparent. When a wave of cold air sweeps over a continent it develops in one a pneumonia, in another a rheumatism, in another a fever or an attack of neuralgia, upon the great majority no bad effects whatever. Can it be doubted that some definite imperfection which ​constitutes the diathesis must have preëxisted to each of the diseases named, even though it was in no manner obvious to the most careful observer?
Acute, chronic, diathetic, or incubative disease may therefore be regarded as merely expressing the various gradations of morbid processes, from the very rapid to the very slow, from the very severe to the very mild, and from the most readily perceived to the imperceptible.
As acute diseases are only compatible with life for short periods, they are rarely transmitted; in fact, they are excluded from the list of diseases properly inheritable. The open chronic forms of disease, such as scrofula and syphilis, are not unfrequently handed down to the offspring, but far oftener is the heritage of the diathetic grade. This is better tolerated, or more compatible with the continuance of the life in the blood than the open chronic forms which quite commonly render the procreative act abortive.
Before bringing our subject to its practical bearings, it seems necessary that the reader should divest his mind of any vestiges of the glamour of superstition which has so long been around the reproductive process. Darwin succeeds in this with admirable directness by putting reproduction simply as a process of growth. Two cells with somewhat diverse qualities commingle and by gradual accretion develop individual peculiarities. The new self-multiplying stream of blood sometimes appears as if derived in unequal proportions from the two progenitors. This may, however, be supposed to arise from another cause, a temporary or permanent prepotency of the gemnules of one parent over those of the other, which gives them greater activity and power of fission. Be this as it may, every new blood-stream is but a continuation of two older, wonderfully compressed at the junction. The preëxistent forms and forces are only slightly modified by mixture, and by the influence of some variable conditions. In all the general outlines of qualities it is the same blood, exhibiting the same tendencies near or remote to good or to evil, to health or to disease. If there has been a slow struggle—often so subtile as to be at times occult in the parental organism between the tendency to the maintenance of a permanent type and some morbid predisposition—the same is almost certain to be carried on in the blood of the child. The leading causes of any divergence from the continuation of the struggle consist in the crossing of blood, and in the application of modifying conditions when impressibility is at its acme, as from germinal coalescence to adolescence.
With the foregoing facts and deductions in mind, and ranging them around what Dr. Farr terms the great hygienic problem—how to free the people from hereditary disease—the solution does not appear as hopeless and difficult as has been supposed. On the side of release is the great conservative principle of reversion; on the side of continued ​subjection are the existing taints or defects of blood, and the continued application of their genetic causes. The third factor is what in political phrase "holds the balance of power." The tendency to the maintenance of durable types is in limine more potent than abnormal variations, else recovery would be the exception instead of the rule. But, if the genetic influences of a defect or of an abnormity be kept in continual action after its inception, the ultimate triumph of reversion is a very rare outcome. Great care in acute diseases is commonly taken that the third factor shall not turn the scale against the tendency to reversion, far less is expert systematic supervision as to this brought to bear in chronic disease, while in the diathetic there is as a rule worse than a fitful, or no care—the misjudged application of causes best calculated to increase and intensify the defect or taint in the blood. In illustration of the statement in reference to acute disease, take a case of pneumonia, the result of a protracted out-door exposure to a sudden fall of temperature, with an abundance of atmospheric humidity. Suppose these genetic conditions continued throughout the attack, the likelihood of reversion gaining the mastery would be reduced to a very small ratio. Yet this is the very course generally adopted by those who have a diathetic defect in their blood, actually oftentimes under the belief that it is the best mode of hindering the full development of a dreaded inheritance. Take for example that of pulmonary consumption. Its leading genetic causes are, an in-door sedentary life, unwholesome food for the stomach, and above all depraved and unwholesome air-food for the lungs. Yet the father and mother with this taint in their and their children's veins, realizing that their boys and girls are delicate, from the moment of birth upward seclude them far more than ordinary in close, ill-ventilated rooms, they coddle and pamper them with unwholesome delicacies, and in effect carefully attend to the very conditions which secure weak and foul air as nutriment for their lungs and blood. Thus it is that the precise causes which originate the defect are with more than ordinary assiduity kept in constant action, and the tendency to reversion utterly overwhelmed.
Every candid person will acknowledge that this is no fancy picture, but a true outline of the practices in nearly every household which has such a shadow over it, so that, if the complete supremacy of reversion over a diathesis is not often seen when compared with the frequency with which it gains the mastery over acute disorders, the difference in results is what might be anticipated, as the unfavorable influence of a third factor is brought to bear on the former and not on the latter. The power of reversion in acute disease is readily discerned, the necessity of observing favoring conditions well known; they are under expert supervision and not difficult to carry into effect. Precisely the opposite is true concerning a diathesis. In chronic disease the struggle between reversion and morbid tendency is often so mild and slow as to be almost imperceptible; in the diathesis it is as a rule entirely so, ​only made obvious now and then before development by some mild aggravating cause, such as, when toward dyspepsia, by slight sensations of discomfort after hearty meals; when toward tuberculosis, by frequent signs of catarrh after ordinary weather-changes.
Not so much by plain evidences to the senses as by mental analysis can the reality of a struggle between a diathesis and reversion to the normal type be apprehended. Yet it is only the vis medicatrix naturæ of medical writers carried from the very obvious in acute disease to the less perceptible in chronic, and to the imperceptible in the diathetic. Although the opinion is very generally entertained that those who inherit a diathesis should be careful as to their mode of life, what effect there is on practice is commonly more injurious than beneficial. This arises from the lack of expert supervision, and the sway of some popular traditions as shallow as they are unsound. More frequently does their observance act as aids instead of hindrances to the development of an inherited dyscrasia. Then the observance of the true conditions which favor reversion in an inherited diathesis require no little judgment, self-denial, patience, and intelligence. In acute disease the physician and nurse see that the conditions of reversion are duly observed. Reputation, love, and alarm are all brought to bear for their enforcement. In a diathesis none of these are evoked until the development of all its signs renders the fact apparent that the fatal work has reached its culminating stage. The diathetic subject while in good health is himself indifferent and incredulous as to his danger. For the young to be always as careful of their health as an invalid, in other words, not to live and do as the careless multitude, presupposes unusual self-denial and discretion. Obstacles like these not only thwart the principle of reversion, but contrariwise strengthen and evolve abnormal variations.
Advantage being carefully taken of reversion in acute disease, less so in chronic, and scarcely at all in diathetic, that the eradication of unfortunate inheritances should have received so little credence is the natural outcome of the prevailing ignorance or neglect of the conditions. It is well, however, to bear in mind that this prevailing belief is simply and wholly the result of antecedents as they are and have been, not as they might and should be.
The instances in which the operation of the law of reversion has had anything like an unimpeded sway are far more commonly casual than designed. Circumstances render a change of environment and habits of life necessary or desirable, and these may happen to include its favoring conditions, or they may not. Those who recover from the tendency to an abnormal inheritance through intelligent design ought to be found, if anywhere, in the ranks of the medical profession, and especially among those of them who have given the science of health no little attention. A work assigned me by the American Medical Association brought some statements under my eye which confirm this ​inference in the most unmistakable manner. I select a few examples in reference to the tuberculous diathesis, at once the most prevalent, the most liable to be transmitted, and, according to the prevailing opinion, the least amenable to preventive measures.
A quite old and widely known physician makes this statement: "My father and mother were cousins. Father had hæmoptysis at twenty-eight, and was supposed dying of consumption, but recovered, and died in his sixty-seventh year of cancer of the stomach. He had cicatrices in his lungs. Mother died of phthisis late in life, having given birth to six children. These are all alive. No consumption in any of them, nor in twenty-seven grandchildren and fourteen great grandchildren."
Another highly reputable physician writes: "On maternal side evident tendency to tuberculosis. My only brother—I had no sister—died of phthisis, aged twenty-six. I had hæmoptysis, with cough, repeatedly, between the ages of twenty-two and thirty-five. Wife healthy, and gave birth to five children—ages between thirty and forty-eight. None of them, nor eight grandchildren, have exhibited any signs of pulmonary consumption."
Another writes: "Consumption on father's side, having lost one if not two sisters by the disease. Mother died of it in her forty-third year. Six children were born to them—all alive and healthy, the youngest past his fiftieth year. They are all free from any signs of tuberculosis, as are also thirty-one grandchildren and eleven great grandchildren."
Yet another writes: "Father died of paralysis, mother of consumption; also one of her brothers. Grandmother also died of what is presumed to have been the same disease. Of seven children, varying from forty to sixty, none have shown any pulmonary disease."
These statements are made by physicians well known for their interest in sanitary science. Through their knowledge and influence, they and their kin have been able to take a wise advantage of the power of reversion. As there are hundreds of thousands throughout the land who have this fearful taint in their blood, a knowledge of the true conditions for its renovation becomes of great importance. It is not within the scope of this paper to enter upon details, but this much may be said, that intelligent and unwavering hygienic observances all through life, but especially from birth to adolescence, constitute the cardinal requisites. Not the hygiene, however, taught in almanacs, in gossipy newspapers, or by itinerant sensational lecturers, but by the most accomplished scientists. A thorough mastery of its principles and details, so as to secure a correct application of them at the various periods, emergencies, and contingencies of life, is absolutely necessary. In short, those with an unfortunate inheritance—like those suffering from an attack of disease—need the knowledge of an expert to enable them to take a wise and full advantage of the principle of ​version. If this be attained, and applied vigilantly and continuously, there is, I have no doubt, far more probability of recovery from an unfortunate inheritance than from an attack of ordinary disease. The chief peril in the latter condition lies in the severity of the struggle, the ground of safety in the former in its mild prolongation, whereby the law of reversion can have unimpeded opportunity through the long and steadfast application of favoring conditions to restore the body to its pristine vigor. The thought may occur that not many have the requisites alleged to be needful for the restoration of defective blood. Yet even this has an outcome not to be deplored. High intelligence, and a will subordinate to it, will survive; while feeble minds and groveling instincts will carry the blood on to overt disease, to untimely death, and to extinction.