in regard to senescence, the matter is very different. There we should, indeed, like to have some principle given to us which would delay the rate of senescence and leave us for a longer period the enjoyment of our mature faculties. I can, as you have readily surmised by what I have said to you, present to you no new rule by which this can be accomplished, but I can venture to suggest to you that in the future deeper insight into these mysteries probably awaits us, and that there may indeed come a time when we can somewhat regulate these matters. If it be true that the growing old depends upon the increase of the protoplasm, and the proportional diminution of the nucleus, we can perhaps in the future find some means by which the activity of the nuclei can be increased and the younger system of organization thereby prolonged. That is only a dream of the possible future. It would not be safe even to call it a prophecy. But stranger things and more unexpected have happened, and perhaps this will also.
I do not wish to close without one added word. The views which I have presented before you in this series of lectures I am personally chiefly responsible for. Science consists in the discovery made by individuals, afterwards confirmed and correlated by others, so that they lose their personal character. The views which I have presented to you, you ought to know are still largely in the personal stage. Whether my colleagues will think that the body of conceptions which I have presented are fully justified or not, I can not venture to say. I have to thank you much, because between the lecturer and his audience there is established a personal relation, and I feel very much the compliment of your presence throughout this series of lectures, and of the very courteous attention which you have given me.
To recapitulate—for we have now arrived at the end of our hour—we may say that we have established, if my arguments before you be correct, the following four laws of age.
First, rejuvenation depends on the increase of the nuclei.
Second, senescence depends on the increase of the protoplasm, and on the differentiation of the cells.
Third, the rate of growth depends on the degree of senescence.
Fourth, senescence is at its maximum in the very young stages, and the rate of senescence diminishes with age.
As the corollary from these, we have this—natural death is the consequence of cellular differentiation.