Page:Popular Science Monthly Volume 71.djvu/213

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the end of the second year, only 20 per cent., and thereafter it fluctuates in the neighborhood of 10 per cent, a year until the age of 13. At 14 or 15 there is a fluctuation, an increase, and then the decline goes on again and slowly we see the growth power fading out. Authors are not agreed as to the exact statistical value, and so I will ask to have thrown upon the screen another curve, also representing the percentage increase of boys, and based chiefly upon English tables. For these data I am indebted to my friend Professor Donaldson, of the Wistar Institute in Philadelphia. He finds in these records an increment of a little more than 200 in the first year, but the drop comes during the second year and is startling in its enormous extent and is contrasted with the later less decline. The phenomena may well arouse our attention and convince us that we are approaching a most important scientific question, the question of why the drop comes in this way. In the case of girls, as the next of our slides will show, we can prove the same phenomena with slightly different values. Girls, like the females of other species, grow a little less forcibly, so to speak, than boys. They do not quite

PSM V71 D213 Percentage of annual weight increments in girls from quetelet tables.png

attain a 200 per cent, value for the first year, but they too drop in a similar manner to the boys to about 30 per cent., and away down towards 10 per cent, in the third year. Then comes the long slow gradual decline up to the period of twenty-three. Professor Donaldson, as our next slide will demonstrate to us, has prepared curves from the English figures for girls also. They come up nearer to the 200 per