The problem of age, growth, and death; a study of cytomorphosis, based on lectures at the Lowell Institute, March 1907 . ation. Thephenomena of regeneration are important and very in-structive. We shall come to them presently. It willmake our study of regeneration clearer, more signifi-cant, I think, if we pause for a moment to considercertain fluctuations in the natural development of theorganism. We see, for instance, in the brain that earlythe cells beein to assume the character of nerve cells andthat thereafter their multiplication ceases. But, cur-iously, there will be a spot in the spina
The problem of age, growth, and death; a study of cytomorphosis, based on lectures at the Lowell Institute, March 1907 . ation. Thephenomena of regeneration are important and very in-structive. We shall come to them presently. It willmake our study of regeneration clearer, more signifi-cant, I think, if we pause for a moment to considercertain fluctuations in the natural development of theorganism. We see, for instance, in the brain that earlythe cells beein to assume the character of nerve cells andthat thereafter their multiplication ceases. But, cur-iously, there will be a spot in the spinal cord, for ex-ample, where the change of the cells into nerve cellshas not taken place, and from that growth will go will migrate from that spot and reach their ulti- REGENERATION AND DEATH 187 mate destination. When the child is born it is incapableof movement. There is scarcely more than the powerof twitching about in a disorderly fashion. Its musclescan contract, to be sure, but any sort of motion thatimplies a harmonious working together of variousmuscles, the baby at birth is quite incapable of. Fig. 63. Section of the Cerebellum of a Child of Thirteen the nuclei, which are represented as black dots, are drawn, o. /., outerlayer, which disappears during childhood; tnol, molecular layer; gr, granularlayer. X 120 diams. This phenomenon is doubtless due to the fact thatthe cerebellum, the small brain, is as yet imperfectlydeveloped. If we examine the brain of the child atbirth, we find at the edge of the cerebellum a line alongwhich the production of new cells is going on. Thesenew cells migrate over the surface of the cerebellum i88 AGE, GROWTH, AND DEATH without changing at all into nerve cells. They forma distinct layer, Fig. 63, which is well known to everyinvestigator of brain structure. Soon after birththese cells accomplish a second migration, but in adifferent direction. Instead of moving in a constantcurrent over the surface of the brain, ea
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