Another great source of vitiation of the stream of tendency is found in two people who marry in a truly enough physiological sense, but who find or force themselves in lives of wear and tear which progressively unfit them for childbearing and child nurture. Poorly calculated ambitions, unexpected difficulties to be surmounted, depressing oppositions, with perhaps more or less actual disease or accident, largely account for this in a general way. Obviously, during the child-rearing age, the effect of what parents are obliged to endure and execute upon the fortunes of progeny becomes a matter of far-reaching importance. That anything which persistently exhausts or overstrains the parents must tell in the later dynamic tendency and development is premised at least by certain recent studies, especially those of Hodge on the influence of fatigue, and of Van Gieson on the effects of exhaustion and intoxication upon the nervous elements. (See also Peterson, _op. cit._) In no sense can parents be said to live for themselves chiefly. Always the influence of their own health, happiness, and prosperity upon their children should be remembered, and should be made as constructive as possible. That this can be consciously attempted with commensurate results is more or less evidenced not only by common observation but by investigation. Not, however, in the sense that parents are always able to endow children with some particular, much-wished-for characteristic, as so many suppose--for it must be remembered that perhaps pretty fixed tendencies for several generations may have to be overcome and reversed before such special results can be obtained, but in the much better sense of giving such an impetus healthward and strengthward and lifeward as may later on be the beginning of a constitutional foundation that shall support many generations of full health and longevity.