THE INFLUENCE OF SEX OF FETUS ON LENGTH OF INTER THE following are additional tables and facts (based on nearly a thousand observations), showing that the intergestation period between girls is shorter than it is between the birth of boys, and that girls (first children) are born sooner after marriage than boys (first children)—the whole forming a supplement to a paper recently published by the author, entitled “An Inquiry, Etc." 1 Since the publication of the above-named paper, the author has been fortunate enough, through the untiring industry of his friend, Dr. A. C. W. Beecher, to have tabulated nearly one thousand observations on the length of the intergestation period by sexual differentiation, the deductions from which fully confirm the predictions already made in the paper above referred to. In the compilation of these tables, genealogies were the only available source from which all the necessary dates could be obtained, and the "Genealogy of the Noble Family" presented these figures in the best form for our use. Those families were selected which contained a fair proportion of both sexes, all those consisting only of boys, or only of girls, were excluded, as were also all instances of greater time than three years between births, as indicating illness, temporary separation, or as showing a certain amount of relative sterility. As families of exclusively boys or exclusively girls are exceptional, it is evident that separate tables should be constructed for each of these classes. "An Inquiry Concerning the Relative Influence of the Sex of the Fetus in Utero, on the Mental, Physical, Physiological, Pathological, and Developmental Condition of the Mother during Gestation, and of the Infant during Lactation, and Subsequently." AMERICAN JOURN. OBSTET., New York, February, pp. 113-135; March, 248-263; May, 502-517; June, 602-622, 1884. In the 982 births tabulated from the "Genealogy of the Noble Family," extending over a period of 200 years [1635– 1835], we find that there are: 98 girls born as first children, 14 months and 14 days after marriage. 66 17 103 boys 17 66 66 66 228 boys following the birth of boys at an average interval of 24 mo., 27 d. 24 mo., 16 d. 24 mo., 3 d. 24 mo. In our paper referred to on the first page of this article, under Proposition 17, we have shown that the weight of a child at birth is influenced by the sex of the child which immediately preceded it, as may be seen from the following, elaborated out of Wernich. When a Boy follows a boy he weighs on an average 3,430 grams. By combining these tables, we have: Boys follow boys at intervals of 24 mo., 17 d., and weigh 3,430 gms. 24 66 16" 66 3" The proportion of sexes in births was as follows: 66 450 66 66 First children, 103 boys and 98 girls, or 105 boys to 100 girls. All pregnancies, 532 118 64 ** 100 This table shows that eleven per cent more girls are born in first pregnancies than in all the pregnancies combined. It is a well-known fact that the proportion of girls in illegitimate children is always greater than among those born in wedlock, which may be accounted for in a great degree by their being for the most part first children, and of young mothersthough Schramm has shown from observations based on 1,050 cases, that of old primiparæ, the proportion of males among first children was greater than in births in general, viz., 124 boys to 100 girls, while births in general gave a proportion of only 107 boys to 100 girls. Table Showing the Mean Time between Births, also the Mean Time between a Birth and the Next Succeeding Conception, According to the Sex of the Preceding and Succeeding Fetus, and the Number of the Pregnancy. [Families of all boys or all girls excluded, as also any case of greater time than three years between births. 982 Obs. from the "Noble Genealogy," 17th and 18th centuries, average of about seven children to each family.] FROM BIRTH OF ORDER OF SEXUAL FROM BIRTH OF Order & No. Preg. M'ths. Days. M'ths. Days. M'ths. Days. M'ths. Days. From Marriage to Conception and Birth of First Children by To the birth Sexes. Mean time from marriage of the first child when a girl (98 obs.), 14 mos. 14 days. Hence those women who bore girls in their first pregnancies conceived 3 mos. and 3 days sooner after marriage than those who gave birth to boys, corresponding with the greater rapidity with which girls follow girls, as compared with any other order or combination of the sexes. Ansell's table,' based on 25,000 observations (all pregnancies) gives the average time between marriage and the birth of the first child as 1.32 years (nearly 16 months). In another table, based on 6,035 observations corrected for still-births and twins, he has shown that "the mean interval between marriage and the birth of the first child is nearly sixteen months." It will be interesting to compare our table with the above. We found that From marriage to birth of girl was 14 mos. 14 days. 66 66 Average both sexes... 31 mos. 31 days. This average of 16 mos. is almost exactly the same as found by Ansell, based on a large number of cases among women in another country. From an examination of those cases (among the 982 observed) where the interval between marriage and the birth of the first child and the interval between subsequent birth was less than nine months (the usual period of utero gestation), we find that, following the rule already determined for the general averages, viz., where a child is born in less than nine months after marriage, the girls are on an average born in eight months, and the boys in eight and one-half months after marriage-the difference in the period of gestation with the female sex, as compared with the male, being about a week (8 days), which corresponds with the difference for normal periods, as shown in our paper, "An Inquiry, etc.," as may be seen from the following: 1 Duncan: "On Sterility in Woman." London Lancet, Feb. 24th et seq., 1883. Time of Marriage to the Birth of First Child. Baust,' in his tables, found that boys were carried seven days longer than girls; all of which tends to confirm the generally received opinion, that males are carried longer than females. Among bees this difference is further illustrated in a marked and invariable manner-queens arriving at perfect development in 16 to 18 days; workers (imperfect females), in 21 to 23 days; and drones (males), in 24 to 26 days. Among the 201 first children, in only one instance (a boy), did the birth take place exactly 9 months after marriage. A woman had a girl born 10 months and 11 days after marriage, followed by another girl in 11 months 28 days, this followed by a third girl in 11 months 28 days; then a boy in 20 months 7 days; then a girl in 16 months 27 days; then a boy in 40 months 11 days. A mother of 10 children gave birth to her first child (a boy) 8 months 23 days after marriage; her eighth child (a girl) was born 9 months 5 days after the seventh (a boy). The average interval between the birth of her 10 children was 18 months 20 days. In one case, a boy followed a boy in 11 months 1 day. |