Scientific observation has made us acquainted with some of the agencies which vitiate the quality of the brain, and it is our duty to profit by its results. The principal of them is morbid action in the brain itself, producing, more or less directly, disorder and weakness. But its deteriorating influence does not cease with the individual. In a large proportion of cases it is transmitted to the offspring; and though it may not appear in precisely the same form, yet the tokens of its existence are too obvious to be overlooked.--Another agency scarcely less efficient is that of _neuropathies_, to use the medical term,--meaning the various forms of disorder which have their origin in the brain, and comprising not only epilepsy, hysteria, chorea, and other convulsive affections, but that habit of body and mind which makes a person _nervous_. While they may abridge the mental efficiency of the patient comparatively little or not at all, they may exert this effect, and often do, in the highest degree, on his offspring. The amount of insanity in the world attributable to insanity in the progenitors, and therefore called, _par eminence_, hereditary, is scarcely greater than that which originates in this manner, and of which the essential condition is no less hereditary.--Another agency, acting on a large scale in some localities, is exerted by those diseases which are attributed to some disorder of the lymphatic system, as scrofula and rickets. Though not entirely unknown to the affluent classes, yet it is chiefly in the dwellings of the poor that these diseases find their victims. Cold, moisture, bad air, deficient nourishment,--too frequent accompaniments of poverty,--are peculiarly favorable to their production. The physical depravation thus induced is frequently transmitted to the brain in the next generation, and appears in the shape of mental disorder.--Again, it is now well known that the qualities of the race are depreciated by the intermarrying of relatives. The disastrous influence of such unions is exerted on the nervous system more than any other, and is a prolific source of deaf-mutism, blindness, idiocy, and insanity. Not, certainly, in all cases do we see these results, for the legitimate consequences of this violation of an organic law are often avoided by the help of more controlling influences, but they are frequent enough to remove any doubt as to their true cause. And the chances of exemption are greatly lessened where the marriage of consanguinity is repeated in the next generation. The manner in which the evil is effected may be conjectured with some approach to correctness, but to speculate upon it here would lead us astray from our present purpose. The amount of the evil may be thought to be comparatively small, but they who have a professional acquaintance with the subject would hardly undertake to measure the dimensions of all the physical and mental suffering which it involves. In one State, at least,