WEIGHT, SIZE, AND AGE OF THE HUMAN EMBRYO. 



147 



is more affected than that of the trunk or extremities; thus the head modulus, 

 which is normally less than the sitting height, may temporarily exceed it, due to 

 the formalin distention. In the subsequent shrinkage a fetus of 146 mm. CR, for 

 instance, will regain its normal proportions within 16 months. These changes in 

 the embryo due to formalin preservation have been described by Schultz (1919). 

 To obviate, as far as possible, discrepancies due to formalin, v\ e have made it a 

 rule to record the weight and measurements at about the end of the second week 

 after the specimen has been placed in the fixative. Even with this precaution it 

 will be seen that the distended specimen tends to fall below the curve ; that is, to 

 have a greater weight than it should have for its length, as compared with the aver- 



Fig. 1. — Normal fetuses showing the th 



jhree grades under which they are grouped. -4, grade 1, 

 fetus No. lis.;. CR length 60 mm., weight 19.5 grams; B, grade 2, fetus No. 1282b, 

 CR length 65.5 mm., weight IS grams; C, grade 3, No. 1210, CR length 66 mm., 

 weight 14.2 grams. A is shorter and manifestly younger than the other two, hut 

 owing to its extreme distention by formalin, it weighs more. 



age specimen; on the other hand, macerated specimens rise above the mean curve- 

 that is, they are not heavy enough for their length. This is illustrated in figure 1, 

 in which are shown three fetuses having the following respective measurements 

 and weights: A (No. 1183), 60 mm. long, 19.5 grams; B (No. 12826), 65.5 mm. long, 

 18 grams; and C (No. 1210), 66 mm. long, 14.2 grams. Fetus B shows about the 

 average formalin distention, and although it is a little longer and older than fetus 

 A, the latter weighs more as a result of its tense distention in formalin, which is 

 always the case in such particularly fresh, grade 1 specimens. Fetus C, a grade 3 

 specimen, is the longest of the three, although it weighs considerably less than 

 either of the others. Its great length relative to its weight is due in part to the fact 



