In enquiries upon the influence of heredity in the causation of insanity we rarely get back beyond the third generation. Few men either know, or care much about their great-grandfathers or great-grandmothers, and fewer are willing to keep in remembrance the existence of an ancestral taint. Nevertheless, in studying these subjects we ought to go back as far as we can, and the few pedigrees which have been traced of the genesis of insanity in families bring out deductions of the highest interest. In studying the fortunes of those ruling houses, whose lives are recorded by history, we occasionally trace the rise and extinction of a family through insanity, or we behold the wane and final extinction of the hereditary disease. There is no deficiency in the materials. Mental disease is very common in royal and noble families, and great disasters to nations have sometimes signalised the madness of their rulers.