Page:Popular Science Monthly Volume 71.djvu/121

Rh the spaces allotted to them, the nuclei have become small, and the protoplasm has changed its appearance very strikingly because there have been deposited in it granules of the pigment which impart to these cells an appearance very different from that which they had in their maturity when their functional powers were at their maximum. You will notice also in other parts of the right-hand figure that the atrophy of the cells has led on to their disintegration, that they are breaking down, being destroyed, and that the result of their breaking down will ultimately be their disappearance. Thus the atrophy of a cell may lead to its death. The other two figures upon the screen show us the brain of the humble bee. On the left is the brain of the bee in the condition in which we find it when the bee first emerges from the pupa or chrysalis. The cells are then in a fine physiological condition, but in a few weeks at most the bee becomes old and in the space which belongs to each cell we find only its shrunken and atrophied remnants, the nucleus greatly reduced in volume, and an irregular mass of protoplasm shrunk together around it. These cells have likewise undergone an atrophy and are on their way to death. In other cases we find that there is a change going on which we call necrobiosis, which means that the cells continue to live, but change their chemical organization so that their substance passes from a living to a dead state. No more perfect illustration of this sort of change can be found than that which is afforded by the skin. In the deep layer of the outer skin are the living and growing parts, which we all know from experience are sensitive. As these multiply some of them move up towards the surface; and they are continually shoved nearer and nearer the surface by the growth of the cells underneath. They finally become exposed at the surface by the loss of the superficial cells which preceded them. During this migration the protoplasm of each cell, which was alive, is changed chemically into a new substance which we call keratin, or in common language, horny substance. Ultimately the cell protoplasm becomes nothing but horny substance and is absolutely dead. Here life and death play together and go hand in hand. Hence the term necrobiosis, life and death in one. Another form of degeneration which occurs in many cases is of great interest because it seems as if the cells were making a last great effort; and their final performance is one of enlargement. They become greater in size than before; but there will follow a disintegration of these cells also; and they break down and are lost. This form of degeneration is termed hypertrophic, and represents a third type, as I have stated. In all parts of the body degenerative changes are going on, and they represent collectively a third phase in the cytomorphic cycle. But there is yet one more phase, which is needed to complete the story. That is the phase of the