ABSTRACT
The economic consequences of an age-structure are all too obvious. Biological research is by no means uninfluenced by the economic importunities of the times, and there can be little doubt that the newly awakened interest of biologists in ageing-or the hard cash that makes it possible for them to gratify it-is a direct reaction to this economic goad. The use of the force of mortality as a measure of senescence assumes that all members of the population are equally at risk. The efficacy of most of the known cancer-provoking chemical compounds depends upon the repeated exposure of tissues to their action over long periods. The test-tubes are no longer to be thought of as immortal; on the contrary, after a certain age, as a result of some intrinsic shortcoming, they suddenly fall to pieces. Higher organisms have means for counteracting the cumulative effect of recurrent injuries.
