Abstract
With rising levels of environmental radiation of the ionizing types, and with accumulating evidence that radiation contributes to or accelerates senescence, attention becomes concentrated on aging as an operating process and on the specific role of radiation in this and in other biologic processes. The object of this paper is to take account of genetic transition as a means by which both physiologic and radiologic aging may be produced—in part, if not altogether—and at the same time to make certain pertinent correlations. For the present purposes, aging or senescence is defined as an affliction of the more adult organism, the sequel to which sooner or later is death. Progress of senescence, it is evident, coincides in a general way with passage of time. During the fifth decade of life in man, there begins, as a rule, a noticeable turn toward decreased efficiency of some organs and of the individual as a whole. During the sixth decade, definite reduction in efficiency is apparent almost without exception, and with further passage of time, there comes a cascade of senile changes with death as the end-result— most frequently in about the seventh and eighth decades when individuals live in communities where health standards are maintained at a high level. Oddly, death is seldom attributed specifically to senility. More often, reference is made to the repressive effects of infection, to the failure of one or another of the organs, or to severe emotional shock, as proving sufficient to strike out or extinguish life in senile persons. Cardiovascular disease, as a terminal condition, correlates with an ever-mounting toll of the aging population, but aging can hardly be defined as progressive deterioration of the cardiovascular system, particularly since it is commonly observed that lower forms without contained circulatory systems also grow old and die. Analogies can be drawn comparing the process of aging with the wearing out of mechanical devices. A feeble elderly person can be likened to a worn-out automobile motor or to a clock whose parts no longer function properly. That a piston ring should wear out with use and with the passage of time is logical enough and would be expected of a material which is exposed to surface wear and which is unable to reconstitute itself. This picture does not carry over completely to living systems. In some respects the wearing out of a shoe affords a better analogy, inasmuch as wear is inside the parts as well as on the surface, but even here there is lack of parallel. A fundamental property of living systems—and one, it would seem, that has no counterpart in the world of inanimate objects—is ability to regenerate damaged parts. It is the capacity for reconstitution and autosynthesis, probably more than any other feature, that distinguishes living from non-living things.
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