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* This address, delivered before the Massachusetts Medical Society, as the "Annual Discourse," is essentially, though abbreviated, the same as the author's discussion at Vineland, before the American Association for the Study of the Feeble-Minded, June, 1912.

The methods of patient research and collective investigation which have led to such brilliant results in the study of various diseases in general medicine and surgery are now beginning to be applied to the study of the causation, extent, significance, treatment and prevention of feeble-mindedness -- the synonym of human inefficiency and one of the great sources of human wretchedness and degradation.

The past few years have witnessed a striking awakening of professional and popular consciousness of the widespread prevalence of feeblemindedness and its influence as a source of wretchedness to the patient himself and to his family, and as a causative factor in the production of crime, prostitution, pauperism, illegitimacy, intemperance and other complex social diseases.

The exact number of the feeble-minded in the community is not known. There are probably two to 1,000 of our population, over 7,000 in Massachusetts alone. These cases are found in the families of the rich and of the poor, in the city and in the country. There is scarcely a village or a school district in my state where one or more will not be found. There is no reason for believing there is a greater proportion in my state than in other states or countries.

The fact that feeble mindedness is the result of pathological conditions of the brain, either gross lesions caused by faulty development or by the destructive results of disease, or perhaps numerical deficiency or imperfect evolution of the ultimate cortical cells, makes it obvious that the resulting mental defect is incurable and permanent. If a nerve cell is damaged or destroyed by traumatism or disease, it is gone forever. It is never replace by the multiplication of other similar cells, as may happen in other bodily tissues.

The various known causes of feeble-mindedness occur in two main groups -- the hereditary and the accidental. The hereditary cases are those where the person is feeble-minded because his parents, or other ancestors were feeble-minded. The accidental group includes those who are feeble-minded as a result of environmental causes, without hereditary influence.

The hereditary cases are the most numerous. The recent intensive study of the family histories of large numbers of the feeble-minded by Goddard, Davenport, and Tredgold show that, in at least eighty per cent. of these cases, the mental defect had been preceded by other cases of defect in the immediate family line. Goddard finds that sixty-five per cent. of his institution cases had one or both parents actually feeble-minded. It is believed that this hereditary defect is the result of protoplasmic defect in the germ plasm of the family stock.

There is no doubt as to the potency and certainty of this hereditary tendency. Often the feeble-minded child represents a feeble-minded family. Davenport believes that aside from the Mongolian type, probably no imbecile is born except of parents who, if not mentally defective themselves, both carry mental defect in their germ plasm.

So far as is known, if both parents are feeble-minded, all the offspring will be feeble-minded. If one parent is feeble-minded, it is probable that some of the offspring will be feeble-minded, and the children who are themselves normal will be likely to beget defectives. These normal persons in tainted families who are potential "carriers" of the defective germ plasm may keep up the sequence. If both parents come from tainted families, the probability of defect in the children is much increased. The normal members of tainted families who mate with healthy individuals with no family taint are not so likely to have defective children; indeed, the tendency may be eradicated by judicious breeding-up for several generations. This tendency may be expressed by one or more cases in every generation, or it may skip one generation to reappear in the next. Inheritance is not merely a question of fathers and mothers, but the family tree goes farther back.

Among the probable accidental or environmental causes of feeblemindedness are injuries to the head at birth, blows or falls in infancy, inflammatory brain disease, toxemia from infectious diseases, abnormal mental or physical conditions of the parents, etc., or the absence of certain vital substances from the blood, as in cretinism. Cases of feeblemindedness often occur in families where there has been no mental disease or defect for several generations. But even where the exciting cause is undoubtedly accidental, there is often a strong hereditary predisposition. Similar injuries or causes in sound families do not result in feeblemindedness. In the majority of these cases the environmental causes are only accessory. The real origin of the disease lies in the defect of the germ plasm.