the units of heredity. From this point of view we may say that feeble-minded persons are such as lack one or more mental traits that are socially important.
From this definition it follows that mental defectives differ quantitatively in the number of socially important traits that they lack and qualitatively in the kind of traits and the degree of their social importance. Defectiveness in one important trait only may be called uni-defectiveness; in two traits, di-defectiveness and so we may have tri-defectiveness up to multi-defectiveness. For example, cases are well known of number-defectiveness, attention-defectiveness, memory-defectiveness, imagination-defectiveness, emotion-defectiveness, inhibition-defectiveness, moral-defectiveness, occurring quite without other defects. Well-known unit defects are word-blindness, figure-blindness, word-deafness, tone-deafness and color-blindness. Any of the defects may occur isolated or two or more of them together in one individual. Such defectives are often not recognized as such, if the missing trait or traits have little social importance; but if gentleness gives way to cruelty or self-restraint to self-indulgence the uni-defective becomes a "moral imbecile," and such a moral imbecile may be good at his school work and bright and active in most ways. It is, however, the multidefectives that constitute the main problem of the feeble-minded; for they are fairly common and are a constant drag on that school system which is not adapted to their capacities. Yet among such may be good mathematicians, musicians, mechanicians, etc. It is clear, then, that "feeble-mindedness" is not a simple trait, but a convenient group in which to put all of the socially inadequate.
Can we, in the midst of this heterogeneity find any general "cause" of defectiveness in its varied manifestations? It seems to me we can discover such a cause by attending to various features of defectiveness. First of all we have to recognize that these defects are in general hereditary. There are family strains with color-blindness, stuttering, word-blindness, number-blindness, tone-deafness, and so on. The deficiency of the uni-defective comes from a defect in the germ-plasm of one or both of his parents. In a multi-defective, likewise, all the absent traits are the result of corresponding defects in the germ-plasm of the parents. And if both parents be multi-defectives that combination of germ-cells will be rare indeed that results in anything but a feeble-minded child.
And, secondly, it is to be observed that "defects" are not pathological conditions; they are merely deviations from the normal condition of the adult. For every person shows these defects at some stage of his life and only gradually overcomes them. My nine-months-old son can not talk, nor dress himself, nor attend to his animal needs. He is