In general there is more doubt about the inheritability of some of the insanities than about cases of mental deficiency. The term insanity is merely a loose descriptive one, and we shall gain little definite knowledge about the inheritance of such maladies until we study each separate insane diathesis specifically. Psychiatrists recognize many different forms of insanity, some of them very distinct from others and the product of unrelated underlying causes. Often it is only a question of degree or sometimes a matter of chance as to whether a given individual is certified as insane or not. A neuropathic person who manifests certain anti-social activities is sure to be classed as insane, whereas another individual with the same diathesis in a less degree might pass unrecognized. It is almost impossible in some instances to tell just where the border-line between a neuropathic and a normal constitution lies. Many of the idiosyncrasies of the insane, indeed, are merely exaggerations of characteristics seen in normal people. Recent studies of the psychology of the insane show that most of their hallucinations and delusions are closely related to some previous mental experience they had before becoming insane. And it has been found that the surest means toward removing the obsessions of the patient in curable cases is to ferret out these earlier experiences and correct the wrong impressions regarding them. Again, certain forms of insanity do not become manifest except as special reactions to particular environmental conditions, and if these conditions do not happen to occur, then the neuropathic constitution though existing would not be revealed. Certain critical periods of life such as puberty, pregnancy and the close of sexual life are particularly likely to test out the mentally unstable, although such individuals may have maintained normal mental balance up to the crisis in question.

Not All Insanities of the Same Eugenical Significance.—Of the various kinds of insanity some seem to be of much greater eugenical significance than others, not only because they are strongly heritable, but also because of the periodicity of the attacks. The patient may be repeatedly in and out of the asylum and in his sane intervals wholly unrestrained as far as propagating his kind is concerned. Manic depressive psychoses and dementia precox in the order named represented the largest number of admissions to the Wisconsin State Hospital for the Insane in 1911 and 1912, and both of these very frequently have a hereditary basis. Fig. 36, a chart showing the insanity in a local family as worked out by one of my pupils, is a good example of a recurrent type. The father (Fig. 36, [p. 241]) was about eighty-two years old when the record was made. His memory was poor and he could not talk connectedly, although this was possibly attributable to old age rather than to insanity. His brother, written to in Ireland, stated that to his knowledge there had never been insanity in his side of the family. The mother (2) was insane at nine, again at twenty-nine and again at thirty-six. In her later life she has been in the Mendota Hospital for the Insane five times and in the County Asylum twice. The eldest daughter (3) has been in the State Asylum five times and is now at home. The next daughter (4) spent five months in the asylum in 1885. Another daughter (5) likewise spent a short period in the asylum. Two sons (6, 7) have each spent two periods in the asylum, and a third son (8) has had an attack of insanity. The youngest child died at the age of three. Thus of the eight adult children six have been insane at some time. The cases in this family seem all to be instances of manic-depressive insanity.

Fig. 36

Inheritance of insanity in the L—— family. See text for description.

A Neuropathic Constitution May Express Itself Differently Under Different Conditions.—Some of the difficulties of getting genealogies of specific forms of insanity are obvious from the following quotations chosen from the works of eminent psychiatrists. Kraepelin, for instance, expresses the opinion that: “The psychopathic charge of a family may reveal itself not only by the appearance of mental disorders but also by other forms of manifestation. Here belong before all, those diverse slighter deviations from mental health which go to make up the borderland of insanity: nervousness, states of anxiety and compulsion, constitutional depressions, slight hysterical disorders and forms of feeble-mindedness, tics; also odd characters, peculiarities in mode of living, criminal tendencies, lack of self-control, intemperance, love of adventure, mendacity, suicide on an inner basis.”

From the volume of Church and Peterson on Nervous and Mental Diseases a further confirmatory opinion may be cited: “In determining the factor of heredity we must not be content with ascertaining the existence of psychoses in the ascendants, but must seek, by careful interrogation of various members of the family, for some of the hereditary equivalents, such as epilepsy, chorea, hysteria, neurasthenia, somnambulism, migraine, organic diseases of the central nervous system, criminal tendencies, eccentricities of character, drunkenness, etc., for these equivalents are interchangeable from one generation to another, and are simply evidence of instability of the nervous system. It is the unstable nervous organization that is inherited, not a particular neurosis or psychosis, and it must be our aim in the investigation of the progenitors to discover the evidence of this.”

Certain Forms of Insanity, But Not All, Seem to Behave as Mendelian Recessives.—A number of psychiatrists and investigators of the inheritance of insanities (Rudin, Lunborg, Davenport, Rosanoff, Jolly), although working independently and in different countries, concur in the opinion that manic-depressive insanity, dementia precox and allied psychopathic conditions tend to occur after the manner of a Mendelian recessive. On the other hand such maladies as Huntington’s chorea are transmitted as a dominant and in all probability at least half of the children of an afflicted individual will inherit and manifest the defect. As to inheritance of various other psychoses we have too few accurately charted pedigrees for most types to make very positive statements about their degree or manner of inheritance. Little can be said beyond the statement that there is a decided tendency for various forms to recur in offspring. Where more than one case of insanity occurs in a given family or stock it is strong presumptive evidence that a hereditary defect is at the bottom of it. As Doctor Wilmarth says, “Mental accident may occur in any family, but it is rarely a second case occurs unless there is a tendency to nerve degeneracy.” For example, of 818 insane at the Wisconsin State Hospital for the Insane during the biennium 1909-10, 187, or practically one-fourth were positively known to have insane relatives. Of these, 24 had insane fathers, 31 insane mothers, 30 insane brothers, 23 insane sisters, 25 insane uncles, 21 insane aunts, and 21 insane cousins. Where definite information could be obtained it was found that of the 5,700 admissions of insane patients to the New York state hospitals during the year ending September 30, 1911, 27.7 per cent. of the cases showed a history of insanity in the family and an additional 22.9 per cent. showed a history of alcoholism, nervous diseases and the like.

Grades of Feeble-Mindedness.—As to the various grades of feeble-mindedness, while no sharp lines of demarcation can be drawn, a rough and ready test usually applied is the relative ability of such subnormal individuals to take care of themselves. In all, the conditions exist from birth or shortly after. Idiots are such defective individuals as are unable to take care of themselves even to the matter of guarding against common physical dangers. Their mentality does not progress beyond that of a two-year-old child. Imbeciles can take care of themselves in the cruder physical ways, but are unable to earn their living. Their mental age ranges from three to seven years inclusive. Morons, or the “feeble-minded” in a more specific usage of the term, can under proper direction become more or less self-supporting but they are as a rule incapable of undertaking affairs which demand judgment or involve unrestricted competition with normal individuals. Their intelligence ranges with that of normal children from seven to twelve years of age. The last class grades up insensibly into the shiftless, ne’er-do-well types which exist in every community. It is the hordes of the feeble-minded in the restricted sense that afford our most serious problems to-day. The idiot and the imbecile are usually early and easily recognized and are kept more or less under restraint, but the higher grades of feeble-minded, the so-called moron type, can be detected often only by carefully devised tests.

About Two-Thirds of the Feeble-Minded Have Inherited Their Condition.—Concerning the various types of feeble-mindedness there is strong evidence that heredity is a factor of greater magnitude than in most insanities. All facts point to the conclusion that most mental deficiency is strongly inheritable and that the majority of our defectives of this type come from degenerate stocks. Practically all specialists at the heads of asylums and homes for the mentally deficient concur in the opinion that about two-thirds of the cases are hereditary. For example, Doctor Alfred Wilmarth, superintendent of the Wisconsin Home for Feeble-minded, says: “My own observations, and those of others in this country and Europe, would indicate that at least two-thirds of the feeble-minded have defective relatives.”