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



curve (p. 131) one can take the following readings: End of fortieth week, average 

 fresh weight 3,242.4 grams; end of thirty-sixth week, 2,360 grams; end of thirty- 

 second week, 1,600 grams. I have taken these three determinations for our curve 

 of menstrual age, increasing them bj r 5 per cent to make them comparable to the 

 formalin weight of our tables, so that they become 3,405 grams, 2,478 grams, and 

 1,680 grams, respectively. By the use of the correlation curve in chart 4 they were 

 converted from formalin weight to mean sitting height for the respective menstrual 

 ages; i. e., fortieth week, 362 mm.; thirty-sixth week, 321 mm.; thirty-second week, 

 283 mm. These converted readings were then entered in their respective places 

 on chart 6 as prominent circles and a smooth curve was drawn through them, uniting 

 them with the menstrual curve from our own material of the first 28 weeks. The 

 total curve thus obtained is probably as close an approximation as can be obtained 

 from such records as are at present available. 



Through cooperation with Professor Williams, of the Woman's Clinic of the 

 Johns Hopkins Hospital, provision has been made for obtaining more adequate 

 information on the relation of sitting height to menstrual age for the last 12 weeks 

 of pregnancy. For this purpose a convenient instrument for determining sitting 

 height has been devised by Dr. A. H. Schultz (1920), which is now in routine use 

 in all confinements at the Johns Hopkins Hospital. It is expected that in the course 

 of another five years sufficient data can be secured to properly verify or correct the 

 curve of menstrual age as now given. 



SUMMARY OF DATA. 



Were our embryological material of sufficient proportions it would, of course, 

 be desirable to divide it according to race and sex and to treat it under separate 

 groupings; but as the number of suitable specimens available at present is only 

 704, no attempt at such subdivision is made in this paper. Our data could be 

 increased by utilizing the reports of other observers, but this would introduce 

 discrepancies, due to method or to different criteria as to what constitutes a normal 

 fetus, which would tend to invalidate the results to a degree that would more than 

 offset the advantage to be derived from the larger mass of material. 



By far the greater number of our 704 fetuses are white, and these are about 

 equally divided as to sex. The other races are not sufficiently represented to 

 alter appreciably the general results. The actual distribution is as follows: White 

 males 252; white females 241; negro males 66; negro females 60; other races, males 

 15, females 11; unidentified as to race or sex 59. 



MEAN SITTING HEIGHT AND WEIGHT. 



The mean sitting height and weight for the end of each week of menstrual age, 

 from the eighth week to term, are given in the accompanying table 1 . These figures 

 are obtained from the curves shown in charts 1, 2, and 4. In the table the weekly 

 increment in height and weight is given. It is of interest to note that the weekly 

 increment in height is greatest from the thirteenth to the seventeenth week, reaching 

 a maximum of 15 mm. at the sixteenth week. Throughout the remainder of the 

 fetal period the increase is surprisingly constant, varying between 9 and 11 mm. 

 The relation of the increment in height to the actual height of the specimen, how- 



