WE owe to Minot1 a startling paradox—the view that the rate of senescence is most rapid at the beginning of life and slowest at the end: to quote the fourth of the laws by which he summarized his conclusions, “Senescence is at its maximum in the very young stages and the rate of senescence diminishes with age”. The justification for his view was that the intrinsic or specific growth-rate of the tissues decreases most rapidly at the outset and progressively more slowly afterwards, following a roughly exponential die-away curve (Fig. 1,A). It seemed a reasonable assumption that the senescent state is related to the loss of the power of growth and so the paradox has been widely accepted, notwithstanding the intuitive conviction that the process of senescence is not significant until after the prime of life. The postulated initial, rapid stages of senescence have to be shrugged off as ‘insensible’.