WEIGHT, SIZE, AND AGE OF THE HUMAN EMBRYO. 151 



10 days longer than when computed from the time of fruitful copulation. Mall 

 therefore enters the copulation age in his curve of growth as a line which falls in a 

 position 10 days less than the mean menstrual age. The copulation age in turn 

 is to be distinguished from the ovulation age and the fertilization or true age. 

 Unfortunately, we do not possess sufficient data for man to establish satisfactory 

 curves for the latter two ages. For our purposes, therefore, we have taken into 

 consideration only the menstrual age, the time from the beginning of the last 

 menstrual period. This has the disadvantage of a considerable probable variation 

 but, on the other hand, it has the more than compensating advantage that we 

 are able to obtain these data for a large proportion of the material. 



As stated above, our records justify an age curve for only the first 28 weeks 

 of the fetal period. In fact, the largest part of our records concerns specimens of 

 the first half of pregnancy. This is due to the source of our material, which is 

 chiefly from abortions, the products of which are sent in by physicians. As a rule, 

 the larger specimens are not sent to us. Therefore, the fact that we happen to 

 receive a greater number of younger specimens does not justify the conclusion that 

 interruption of pregnancy is more frequent during the earlier weeks. To construct 

 a perfect age curve, one should have abundant data evenly distributed throughout 

 the whole fetal period, the fetuses should have been normal and living up to the 

 time pregnancy was interrupted, accurate records should have been kept by the 

 physician and the patient, and furthermore the previous menstrual history of the 

 patient should have been normal. These conditions can be adequately met only 

 in operative cases, of which too few are thus far available. To eventually obtain 

 such data will require the systematic cooperation of many institutions towards tins 

 end. In the meantime we must be content with an approximate result such as is 

 given in chart 6. If the outlying dots in this chart are disregarded as due to 

 inaccuracy of the history given by the patient, to irregularities in menstruation, or 

 to the fact that the development of the fetus had ceased some time before its expul- 

 sion, there still remains a consistent cluster of dots along which the curve is laid. 

 While our collection contains fewer specimens from the later than from the 

 earlier months of pregnancy, there is a sufficient number of the older ones to permit 

 a fairly satisfactory correlation between sitting height and weight; unfortunately, 

 however, the clinical records accompanying them are inadequate for the com- 

 pletion of the curve for the menstrual age beyond the twenty-eighth week. It has 

 therefore been necessary to resort to data from other sources. An attempt was 

 made to extend the curve by the use of the excellent data compiled by Meyer (1915) 

 from 2,394 cases at the Johns Hopkins Hospital. The incorporation of his figures 

 however, produces an irregularity in the curve that is apparently due to the large 

 proportion of negro fetuses included among his specimens. It has been shown by 

 Riggs (1904) that, possibly because of inferior nutrition, or perhaps other causes, 

 the negro new-born weighs less than the white. The average weight of the new- 

 born of 227 white multipara? was 3,480 grams, whereas for 168 negro multipara? 

 it was only 3,131 grams. Since our material is predominantly white, I have used 

 the data reported by Zangemeister (1911). In race and living conditions the cases 

 collected from the literature by him would be fairly comparable to ours. From his 



