WEIGHT, SIZE, AND AGE OF THE HUMAN EMBRYO. 



153 



ever, shows a steadily decreasing percentage. Thus the increase in height is 22 per 

 cent during the tenth week, 18 per cent during the twelfth week, and continues to 

 diminish until, between the thirty-eighth and fortieth weeks, it is less than 3 per cent. 

 The actual increment in weight, in contrast to the increment in height, is a 

 constantly increasing one. The rate of increase is uniform except for an accelera- 

 tion between the twenty-eighth and the thirty-second weeks, when it makes maxi- 

 mum jumps of 20 grains, and another acceleration from the thirty-eighth to the 

 fortieth week. The percentage increment in weight is a little over twice that of 

 the percentage increment in height and, like the latter, steadily decreases as the fetus 



Table 1. — Menstrual age with mean sitting height and weight. 



Based on 701 specimens of the Carnegie Collection, distributed as follows: white males 252; white females 241; 

 negro males GO; negro females 60; other races, males 1.5, females 11; unidentified as to race or sex, 59. These data 

 correspond to the curves shown in charts 1, 2, and 4. 



1 Many of the specimens between the twenty-eighth and fortieth weeks were embalmed, and in these cases the weight 

 given is the fresh weight plus 5 per cent. 



becomes larger. Thus, during the twelfth week the fetus gains 44 per cent in 

 weight; during the fourteenth week 42 per cent; during the sixteenth week 33 

 per cent; and so on until, during the thirtieth week, the gain is less than 8 per cent. 



RELATION OF INCREMENT IN WEIGHT TO SITTING HEIGHT. 



The increase in weight, in proportion to the increase in length, is readily deter- 

 mined from the mean curves on length-weight charts 1, 2, and 4. By reading the 

 weight for each millimeter increase in length, one obtains the weight increase per 

 millimeter, and in table 2 the average weight increments per millimeter of growth 

 are given for fetuses from 40 mm. long to term. Specimens under 40 mm. long 

 were not included, because the greater number were measured in their natural 

 curved posture; their length, therefore, is not strictly comparable to that of older 

 specimens whose bodies could be straightened out for the purpose of measurement. 

 In the table the fetal length is divided into 10mm. intervals and the weight increment 

 as given is the average increase per millimeter for the respective intervals. 



