DURING POST-NATAL DEVELOPMENT. 525 



age. The curve labeled C. R. B. is based on data for this and neighboring months 

 of age and represents a tentative type curve for males, the formula for which is 



index = x '_ 1 -0.258. It may be noted that the curve takes a course somewhat 

 similar to that of the typical growth-curve of childhood, although it is a hyperbolic 

 curve, while the latter is a parabolic curve. Further details and illustrative tables 

 relating to the period of infancy are reserved for future publication. From the data 

 presented it is evident that, as a rule, an infant which grows unusually fast in length 

 is apt to be relatively thin, while an infant which grows slowly in length, if healthy, 

 is apt to put on weight. What the limits of normal bodily proportions in infancy are 

 we can not tell from the evidence at hand, but they probably vary from those 

 represented by an index of 0.700 (metric 0.01938) for unusually long infants to 

 1 .200 (0.03322) for short infants. The anatomist in studying the structure of infants 

 should record length, body-weight, and the height- weight index as well as age. 

 The body fat probably varies in quantity more than other structures in the body, 

 so that in studying relative weight of organs it is important to know whether or 

 not we are dealing with infants of average adiposity. 



The period of childhood extends from infancy to adolescence. It is character- 

 ized by well-defined curves of change in relative proportions of the body and in the 

 height-weight index of build. From the standpoint of average age it extends from 

 the sixth or seventh month of infancy to the fourteenth or fifteenth year. From 

 that of average dentition it extends from the eruption of the first incisors 

 to that of the second molars. From that of the height-weight index it 

 comprises a period during which alterations in the index approximate a simple 

 parabolic curve which for inch-pound units and for boys may be expressed as 



413 + 0.6 (x -56) 2 , , . , , . . , , 410 + 0.6(a;-55.5)2 



' where x = height in inches, and for girls as ~7ooo 



Similar curves may be used to express centimeter-gram ratios in terms of the per- 

 centage found by dividing the weight in grams by the cube of height in centimeters ; 

 formulae for these curves are for boys 1.1432+0.000258 (x 142) 2 , for girls 

 1.1349+0.000258 (x 141) 2 . The curves are based on a study of all available data 

 relating to avearge weight and average stature at a given age during childhood. 

 Weight is taken as weight without clothes. Where weight in clothes is given, de- 

 duction for estimated weight without clothes has been made. The data relating to 

 this study are too voluminous for publication here. The figures on which are based 

 the growth-curves of childhood, as well as of infancy and adolescence and maturity, 

 are given in tables H, I, and J. Charts C and D (constructed in a manner similar 

 to chart A described on p. 519) illustrate both the height-weight index growth- 

 curves here described and weight-for-height curves. 



The height-weight-index growth-curves are proposed as type curves of indices 

 of build during childhood in healthy Americans. With them we may compare 

 indices of given individuals or groups of individuals for the sake of estimating their 

 relative build. A low index at a given stature in an undeformed individual indicates 

 a thin body; a high index indicates a stocky and usually a fat individual. The 

 heavy lines drawn through charts C and D represent the typical growth-curve 



