Page:Popular Science Monthly Volume 70.djvu/492

488 of the body. Now in the very young the bulk of the body is not great, but the loss of heat is very great, and this perhaps can be most readily explained to you if you imagine that you hold in one hand a very small potato and in the other a very large potato, both of which have come at the same moment from the same oven, and that you have just started out for a cold winter drive. You all know, of course, that in a little while the small potato, though it was as hot as the large one at first, will have lost its heat, will no longer serve to keep the hand warm, but the other hand, in which the bulkier potato is held, in which the volume of the heat—we might so express it, perhaps—is correspondingly great, benefits by the retained heat a long time. Essentially similar to this is the difference between the child and the adult. The child loses heat with comparatively great rapidity—the old person at a comparatively slow rate. Hence it is necessary for the child to produce more warmth in order to keep up the natural normal temperature of the body. When, therefore, we find that in the old person the respiration is diminished, and that the production of carbon dioxide from the lungs is greatly lessened, we are not immediately to jump at the conclusion that the quality of physiological action has been debased—that we see here a sign of decrepitude. On the contrary, the change is the result of physiological adaptation, of suiting the performance of the body to its needs. This is one of the great wonders, one of the mysteries of life, of which we here have a sample, the constant adaptation of the means to the end. That which the body needs is done by the body. A child needs more warmth, and its body produces more; the old person needs less warmth, and his body produces less. How this is accomplished we are unable to say, but constantly we see evidence of this purposeful accommodation on the part of the body—what is called by the physiologists the teleological principle, the adaptation of the reaction of the body to its needs. There are innumerable illustrations of this, many of which are of course perfectly familiar to us, although perhaps we do not think of them as illustrations of this great law of nature. As, for instance, when we eat a meal, and the presence of food in the stomach calls into action the glands in the wall of the stomach by which the digestive juice is secreted. The juice is produced exactly at the time when it is needed. Innumerable, indeed, are the illustrations of this fundamental principle.

There is another class of phenomena characteristic of the very old which will perhaps seem a little surprising to you after the general tenor of my previous remarks. I refer to the power of repair. This, modern surgery especially has enabled us to recognize as being far greater in the old than we were wont to assume; and we know that there is a certain luxury, a certain excess reserve in the power of repair, and that we may go far beyond the ordinary necessities of our