Page:Popular Science Monthly Volume 71.djvu/199



Ladies and Gentlemen: In the first of the lectures, I described those grosser characteristics of old age, which we ourselves can readily distinguish, or which an anatomical study of the body reveals to us. In the second lecture I spoke of the microscopic alterations which occur in the body as it changes from youth to old age. But besides the changes, which we have already reviewed, there are those others, very conspicuous and somewhat known to us all, which we gather together under the comprehensive term of growth. It is growth which I shall ask you to study with me this evening, and I shall hope, by the aid of our study, to reinforce in your minds the conclusion which I have already indicated, that the early period of life is a period of rapid decline, and that the late period of life is one of slow decline.

In order to study growth accurately, it is desirable, of course, to measure it, but since we are concerned with the general problem of growth, we wish no partial measure, such as that of the height alone would be. And indeed, if we take any such partial measure, how could we compare different forms with one another? The height of a horse is not comparable to that of a man; the height of a caterpillar is not comparable to that of any vertebrate. Naturally, therefore, we take to measuring the weight, which represents the total mass of the living body, and enables us at least with some degree of accuracy to compare animals of different sorts with one another. Now in studying this question of the increase of weight in animals, as their age increases, it is obviously desirable to eliminate from our experiments all disturbing factors which might affect the rate of growth or cause it to assume irregularities which are not inherent either in the