period of higher diversified life is purchased at the price of ultimate death.
Minot has added to this fundamental idea certain views as to quantitative relations of nuclear and cytoplasmic material in the cell. Relative increase of cytoplasm is taken to be the beginning of the process of aging, while relative increase in nuclear material is considered a process of rejuvenation. Such rejuvenation was held therefore to occur in the early cleavage of the egg, since here the amount of nuclear material was supposed to increase greatly in proportion to the amount of cytoplasm.
The recent important paper of Conklin has shown that in the cleavage of many animals this increase of nuclear material relative to the cytoplasm does not occur. Conklin's results will apparently go far in rendering untenable or modifying all theories in which great significance is attached to the precise quantitative relations between nucleus and cytoplasm. But what is important to realize is that this has no bearing on the fundamental feature of the theory that aging and death are due to differentiation. The grafting of the theory that the quantitative relation between nuclear and cytoplasmic material is an essential point upon this general theory was unfortunate from the beginning.
Everything points, it appears to me, to the essential correctness of the view which holds age and death to be the result of the greatly increased differentiation of larger organisms. Is there then any probability that we shall some time find that in the higher animals, as in the lower ones, death need not occur?
Evidently not. If death is the price of differentiation, then after the goods have been delivered the price must be paid. To prevent a higher organism from undergoing death would at the same time prevent him from becoming a higher organism. And the cell which remains in the embryonic condition—the cell of the germ glands—is even now as immortal as the cell of the infusorian. Death, as Minot says, is the price we pay for our more complex life. Age and death, though not inherent in life itself, are inherent in the differentiation which makes life worth living.