begun to slow down, the backward ones may still be growing rapidly, and so making up (more or less completely) to the others. In other words, the period of high positive correlation between stature and increment will tend to be followed by one of negative correlation. This interesting and important point, due to Boas and Wissler31, is confirmed by the following table:ã
| Age | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Stature | (B) | 112ôñ7ã | 115ôñ5ã | 123ôñ2ã | 127ôñ4ã | 133ôñ2ã | 136ôñ8ã | 142ôñ7ã | 147ôñ3ã | 155ôñ9ã | 162ôñ2ã |
| (G) | 111ôñ4ã | 117ôñ7ã | 121ôñ4ã | 127ôñ9ã | 131ôñ8ã | 136ôñ7ã | 144ôñ6ã | 149ôñ7ã | 153ôñ8ã | 157ôñ2ã | |
| Increment | (B) | 5ôñ7ã | 5ôñ3ã | 4ôñ9ã | 5ôñ1ã | 5ôñ0ã | 4ôñ7ã | 5ôñ9ã | 7ôñ5ã | 6ôñ2ã | 5ôñ2ã |
| (G) | 5ôñ9ã | 5ôñ5ã | 5ôñ5ã | 5ôñ9ã | 6ôñ2ã | 7ôñ2ã | 6ôñ5ã | 5ôñ4ã | 3ôñ3ã | 1ôñ7ã | |
| Correlation | (B) | ôñ25 | ôñ11 | ôñ08 | ôñ25 | ôñ18 | ôñ18 | ôñ48 | ôñ29 | ããôñ42 | ããôñ44 |
| (G) | ôñ44 | ôñ14 | ôñ24 | ôñ47 | ôñ18 | ããôñ18 | ããôñ42 | ããôñ39 | ããôñ63 | ôñ11 |
A minor, but very curious point brought out by the same investigators is that, if instead of stature we deal with height in the sitting posture (or, practically speaking, with length of trunk or back), then the correlations between this height and its annual increment are throughout negative. In other words, there would seem to be a general tendency for the long trunks to grow slowly throughout the whole period under inôÙvesôÙtiôÙgaôÙtion. It is a well-known anatomical fact that tallness is in the main due not to length of body but to length of limb.
The whole phenomenon of variability in regard to magnitude and to rate of increment is in the highest degree suggestive: inasmuch as it helps further to remind and to impress upon us that specific rate of growth is the real physiological factor which we want to get at, of which specific magnitude, dimensions and form, and all the variations of these, are merely the concrete and visible resultant. But the problems of variability, though they are intimately related to the general problem of growth, carry us very soon beyond our present limitations.
Rate of growth in other organisms .
Just as the human curve of growth has its slight but well-marked interruptions, or variations in rate, coinciding with such epochs as birth and puberty, so is it with other animals, and this phenomenon is particularly striking in the case of animals which undergo a regular metamorphosis.
In the accompanying curve of growth in weight of the mouse (Fig. 12), based on W. Ostwaldãs observations32, we see a distinct slackening of the rate when the mouse is about a fortnight old, at which period