Now, the outcome of such marriages seems to be a vitiated stream of tendency, which carries with it in its progress from generation to generation certain elements which predetermine to still fuller vitiation, even with incurable insanity, as noted above. Thus, people endowed with such natural characteristics, being altogether too prone to gravitate toward each other, eventually marry, and thus emphasize in progeny the vitiation already doubly initiated. Nature's course demands that such people marry, if at all, into the healthiest, most corrective stock possible. But here immediately there arises not only a scientific prohibition, but an ethical question which should be heeded: Should such people really marry even the best of stock, with the probability of thus vitiating a stream which until this time has evidently been becoming clearer and stronger? Again, people who are constitutionally tending to mental breakdown are very apt to load themselves down with duties and get themselves into situations which must necessarily prove to be too onerous and too perplexing for their poorly developed strength and skill. Of course, circumstances often require this. Many times, however, there is a kind of impulsive restlessness coupled with a short-sighted optimism, both constitutional, which, altogether more than ordinary circumstances, are to blame for undue assumption of work or care, and whose effect is, perhaps, best seen in the persistent tendency of such people to originate and perpetuate exhausting habits, both of mind and body. Thus, the habit of self-poisoning from poorly digested and poorly assimilated food is easily acquired by such people, and always becomes a source of progressive brain starvation and often of consequent mental breakdown. Says Dr. A. S. Thayer (Journal of Medicine and Science, vol. iii, page 173), "There is ground for belief that exhaustion--fatigue--is dependent upon poisoning of the cells of the brain, muscles, and other tissues by the waste products of functional activity."[D] Again, as already noted, perversions of the natural instincts--of appetite for food, of desire for gain, of social or other ambitions, and especially of the sexual impulse and its habitual indulgence--fasten themselves upon such individuals with a permanence and destructiveness that must almost of necessity lead to disaster.[E] And so we may see that as a most natural, although often a far-removed, result of unphysiological marriages, proceeding through generations which have been thus predestinated to weakening choices and practices, insanity finally appears to mark the ultimate extent both of the mental disorganization and bodily inefficiency, which extent is owing not only to the original initiating steps, but also to subsequent stages of causation, progressively developed from generation to generation.