DURING POST-NATAL DEVELOPMENT. 489 



would be 4050 cubic inches. If he were 68 inches tall the volume of his body would 

 occupy - ~ of a space equal to the cube of his height or, expressed in terms of per- 



ol44o 2i 



centage, 1.288 per cent. The body of an individual 50 inches tall and of the same 

 shape would occupy the same proportions of the cube of his height, or 1.288 per cent 

 of 125,000, 1610 cubic inches. At 27 inches to the pound this would mean a weight 

 of 59.6 pounds. Similarly, an individual 20 inches high of the same form would 

 have a volume of 103.04 cubic inches, and a weight of 3.81 pounds. Conversely, if 

 the ratio of volume of the body to the cube of the height differs in two individuals 

 the form of the body of the two individuals must differ. Thus it is clear that if the 

 volume of the body of one individual occupies a greater part of the space equal to 

 the cube of his height than is the case with another individual, the first individual 

 must have a relatively greater transverse section. If a new-born infant 20 inches 

 long weighs 7.34 pounds, assuming that a pound is equal to 27 cubic inches, his 

 volume would be 198.18 cubic inches. This volume would occupy 2.477 per cent 

 of a space equal to the cube of his height, or nearly twice as much as if he had the 

 form of the 150-pound man referred to above. His relative transverse cross-section 

 would therefore be about twice as great. By correlating this difference of ratio 

 with difference in body form we are enabled to use the ratio as an index of specific 

 differences of form in so far as the correlation holds. Since individuals do not 

 develop uniformly and vary in body form at all stages of development, the correla- 

 tions of the ratio above mentioned with body form can be at best merely approxi- 

 mate, but with its limitations it is of great value as an expression of build. 



For practical purposes it is more convenient to divide the weight directly by 

 the cube of the height and to use the product as the height-weight coefficient or 

 index of build, rather than to estimate volume from the weight and use the ratio 

 described above. On the assumption that a pound of human body occupies 27 

 cubic inches of space, the height-weight index is of this ratio. Thus a man 68 



at 



inches tall, weighing 150 pounds, would have a height-weight index of : - or 



0.000477, which is of the volume-cube of height ratio 0.01288. Similarly, the 



2ii 



infant 20 inches long, weighing 7.34 pounds, has a height-weight index of 0.0009175 

 or of the volume-cube of height ratio 0.024773. Since the indices just described 



at 



are inconvenient to use freely, owing to the position of the decimal point, we may 

 multiply each index by 1,000 and thus express it in terms of thousandths or of per- 

 centages. Thus the index 0.000477 becomes 0.477 or 47.7 per cent, a form of expres- 

 sion easy to remember and understand. We reach the same result by dividing the 

 weight in pounds by the cube of a tenth of the height or by the thousandth part of 

 the cube of the height in inches. Therefore, as a height-weight index in the study of 

 stature, weight, and body-form, we have adopted the weight of the body in pounds 

 divided by the thousandth part of the cube of the height in inches. Using this 

 index, we find infants during the first half of the first year after birth usually have 

 an index in the neighborhood of 0.918; that is, the weight of the body usually approx- 



