Prenatal Growth of the Human Body. 125 



corresponding ages, in spite of his statement that ''Niir solche Kinder 

 verwendet werden deren Mutter den Tag der Conception genau an- 

 zugeben wussten." Hennig (19) has published a curve of groAvth 

 in fetal weight, but without the data upon which it is based. His 

 curve shows a marked increase in the growth rate in the 6th and 8th 

 months, followed by retardations in the 7th and 9th months. Donald- 

 son (12) believes that a new phase of growth in the human fetus 

 begins with the 6th month, where the curve of absolute growth begins 

 to rise more rapidly. A study of the growth imte, however, as ex- 

 pressed by the figures for the relative monthly growth rate in Table 

 III (or corresponding figures in Fehling's table) reveals no evidence 

 of any marked change at this particular time. 



All of the data being considered, it seems most probable that the 

 normal curve of fetal growth is fairly regular, though the uncertainty 

 regarding the age of specimens and the degree of individual variation 

 makes it very difficult to determine this curve accurately. The curve 

 as drawn (curve 3, Fig. 1) is fairly regular, corresponding roughly 

 to the formula v ^ x^, or 



Weight (g) = ^^ ^ J 



From this formula, the weight may be calculated approximately 

 from the age, or vice versa, for any time beyond the first month. By 

 some such growth formula the age should be determined more accu- 

 rately than by the length (which theoretically should vary as the 

 cube root of the volume, or weight)."* The majority of previous 

 investigators have concluded that for determining the age, the length 

 is a more reliable criterion than the weight ; probably because the 

 skeleton, which determines the length, is thought to be less variable 

 than the soft parts, which make up most of the weight. This is 

 still an open question, however. 



^Roberts (40) has worked out a rule, assuming that the weight increases 

 as the cube of the age ; but this results in figures somewhat too high for 

 the average weight at tlie various months. This is also the case with the 

 formula: Weight (g) = 50 (months — 2)^ recently proposed by Tut- 

 tle (42). 



