Among the predisposing causes heredity includes nearly or quite 75 per cent. of all cases, and is easily first; in considering which not only the immediate parents are to be taken into account, but also the collateral branches, grandparents, uncles, aunts, sisters, brothers, and cousins, for {114} hereditary insanity often skips one generation, and even appears, sometimes, first in the child, then later in the parent. An insane parent may have several children, of whom some may be exposed to the exciting causes of insanity and become insane, transmitting their disease, intensified or not, to their children, while others may avoid the exciting causes of mental disease, escape insanity, but yet transmit to their children a temperament predisposing them to disorder of the mind, which becomes the starting-point for actual mental disease as soon as the exciting causes are sufficient to develop the taint. If the exciting causes do not appear, however, in that generation, and wise marriages are made, the stock returns to the normal healthy standard and the disease disappears from the family. The same form of disease, too, is frequently not transmitted from parent to child or grandchild, but the neuroses, the psychoneuroses, and the cerebro-psychoses, the degenerative forms and the developed forms, are interchangeable. In the ancestry of insanity we find not only actual cerebro-mental disease, but epilepsy, brain disease due to syphilis, habitual drunkenness, any of the severe neuroses, apoplexy, pulmonary consumption, a closely-allied disease, and suicide. Very often the patient's friends think that there is no hereditary predisposition to mental disease, when the physician trained to study such cases would discover so strong a taint that he would not expect all of several children to escape insanity or some of its allied diseases even in a case where there had not been actual insanity in the family for several generations. For instance, where one parent is habitually using alcoholic liquors to such a degree as never to be drunk, and yet rarely quite himself, with the other a sufferer from one of the severe neuroses or cerebral diseases, a single child from such a marriage might stand a fair chance of inheriting and retaining mental health, but if several children should be born the chances that all would escape mental disorder are few. Again, if one parent were the victim of that intense intellectual strain and moral perversion so often seen in the eager pursuit of position and wealth, and the other, straining to keep up in the race, died early of pulmonary consumption, if there had been in the family cases of convulsions, chorea, apoplexy, or suicide, and if some member were hysterical or, without sufficient external cause, unreasonable, anxious, irritable, full of baseless fears, there might have been no insanity in the family, and yet a tendency to insanity might be transmitted to a considerable proportion of the offspring.