488 POPULAR SCIENCE MONTHLY 



perature 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. Es- 

 sentially 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 immedi- 

 ately 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 suit- 

 ing 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 re- 

 pair, and that we may go far beyond the ordinary necessities of our 



