. Carnegie Institution of Washington publication. 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 w
. Carnegie Institution of Washington publication. 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 grams; B, grade 2, fetus No. 1282b, CR length mm., weight IS grams; C, grade 3, No. 1210, CR length 66 mm., weight 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, grams; B (No. 12826), mm. long, 18 grams; and C (No. 1210), 66 mm. long, 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,
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