Let us make still another counterproof by means of figures; let us take an adult with a stature of 1.70 metres and a weight of 19 kilograms; and a three-year-old child 0.90 m. tall and weighing 55 kg. (the normal weight of a child of four). In the case of the adult one centimetre of stature will weigh 65000/170 grams = 382 grams; while one centimetre of the child's height will weigh 15000/90 = 166 grams. In other words, one average centimetre of the child's stature weighs less than one centimetre of the adult, as it naturally should, while the ponderal index on the contrary is 23.6 in the case of the adult, and 27.4 in that of the child.
The reciprocal relations between stature and weight vary from year to year. In babyhood, the child is so plump that the fat forms the familiar dimpled "chubbiness," and Bichat's adipose "fat-pads" give the characteristic rotundity to the childish face; while the adult is much more slender. A new-born syphilitic child which, with a normal length of 50 centimetres, weighed only two kg.—and consequently would be extremely thin—would have the same identical ponderal index as an adult who, with a stature of 1.65 m., weighed 100 kg.
The evolution of the ponderal index forms a very essential part in the transformations of growth; and it shows interesting characteristics in relation to the different epochs in the life of the individual.
In this connection, Livi gives the following figures, for males and for females; from which it appears that at some periods of life we are stouter, and at others more slender; and that men and women do not have the same proportional relation between mass and stature.
| Indices | Indices | ||||
|---|---|---|---|---|---|
| Age in years | Males | Females | Age in years | Males | Females |
| 0 | 29.7 | 29.6 | 15 | 23.1 | 23.4 |
| 1 | 30.9 | 30.5 | 16 | 23.4 | 23.6 |
| 2 | 28.7 | 28.9 | 17 | 23.1 | 23.7 |
| 3 | 27.5 | 27.3 | 18 | 23.2 | 24.1 |
| 4 | 26.5 | 26.6 | 19 | 23.4 | 24.1 |
| 5 | 25.8 | 25.6 | 20 | 23.5 | 24.1 |
| 6 | 25.1 | 24.8 | — | — | — |
| 7 | 24.4 | 24.1 | 25 | 23.7 | 24.1 |
| 8 | 24.0 | 23.8 | 30 | 23.8 | 24.1 |
| 9 | 23.5 | 23.5 | 40 | 23.9 | 24.7 |
| 10 | 23.1 | 23.2 | 50 | 24.3 | 25.3 |
| 11 | 22.8 | 23.3 | 60 | 24.6 | 25.3 |
| 12 | 23.1 | 23.6 | 70 | 24.5 | 24.9 |
| 13 | 23.4 | 23.5 | 80 | 24.4 | 24.7 |
| 14 | 23.1 | 23.3 | — | — | — |
It may be said in general, so far as regards the age, that the following is the established law of individual evolution: during the first year the ponderal index increases, after which it diminishes up to the period immediately preceding puberty (eleventh year for males, tenth year for females), the period at which boys and girls are exceedingly slender. After this, throughout the entire period of puberty, the ponderal index seems to remain remarkably constant, oscillating around a fixed figure. At the close of this period (seventeenth year for males, fourteenth for females), the ponderal index resumes its upward course (corresponding to the period in which the transverse dimensions of the skeleton increase, and in which the individual, as the phrase goes, fills out), and it continues to rise well into mature life (the individual takes on flesh); until in old age, the ponderal index begins to fall again (the soft tissues shrink, the cartilages ossify, the whole person is shrunken and wasted.)
Fig. 38.
Women, during their younger years are on a par with men in respect to the ponderal index, but in later life surpass them, because of woman's greater tendency toward embonpoint, since she is naturally stouter and plumper than man, who is correspondingly leaner and more wiry.