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POPULAR SCIENCE MONTHLY

of these lectures, and I have led you, I hope, to the appreciation of the idea that in cytomorphosis we have at least a part of the explanation of old age. We have learned that the young cells which are produced by the segmentation of the ovum in the body in large part changed into old cells, and also that old cells can not go back in their development and again become young; so that one might easily be led to the suspicion that there could be no possible new young, a conclusion obviously absurd, for there is a constant renewal of the generations. Some

PSM V71 D462 Segmentation of the ovum of planorbis.png

Fig. 52. The Segmentation of the Ovum of Planorbis, to show the earliest phases of development of the egg of a pond snail. Alter Carl Rabl.

device, therefore, must exist by which that which is young is perpetuated, for that which is old can not again become young, and of that device I should like to say something this evening.

As a preliminary to the discussion of this interesting phenomenon, it is necessary to say a few more words in regard to the nuclei. You recall that the units, out of which the body is constructed, the cells, consist each of a little mass of protoplasm with a central body called the nucleus; and you will, I hope, recall that the increase of the protoplasm and the subsequent differentiation of the cell we looked upon as the cause of old age, and the increase of the nucleus as the cause of youth, of rejuvenation. In addition to what has been said concerning