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POPULAR SCIENCE MONTHLY

cent, than in Mühlmann's table, but drop well below 30 per cent, in the second year, and down to 20 per cent, in the fourth. Then occurs the slight increase of growth in the period of twelve, thirteen, fourteen years, and next the final stage of decline. In the four cases the human rate curve is similar. The great fall takes place at the beginning, the slow fall towards the end. Professor Thoma has thought he could get somewhat more accurate results by putting boys

PSM V71 D214 Percentage of annual weight increments in girls by h h donaldson.png

Fig. 33.

and girls together, and he has made a calculation, as shown now upon the screen, of a curve in which the two sexes are combined. His figures again differ somewhat from those we have considered, but you meet in this curve also the same general phenomena. There is an enormous percentage of growth during the first year; an enormous drop during the second; then the slow decline; the moderate fluctuation upward; and then the last slow disappearance of growth. In every instance, therefore, we have an absolute demonstration, it seems to me, of the strange phenomenon. Paradoxical it will sound, whenever it is first stated to any one, that the period of youth is the period of most rapid decline; that the period of old age is that in which decline is slowest. We shall learn in the next lecture that this double phenomenon furnishes us a clue to further investigations, and leads to certain new inquiries, which enable us to gain some further insight into the essential nature of the phenomena of age.