If, again, domestic animals when well nourished give birth to an excess of female offspring, and when ill nourished and overworked to an excess of male offspring, in the former case we can only regard the excess of female births as a pathological phenomenon, inasmuch as a superabundant supply of nutriment is not that which furnishes the highest powers or is most suited to the preservation of life. Again, the accounts given by fur-dealers are quite untrustworthy, since these men commonly obtain their goods at third and fourth hand; moreover, most of the animals whose pelts form articles of commerce, are beasts of prey, such as the otter, the lynx, the bear, the wolf, the fox, etc.—and these animals have no “pasturage.” Among vegetable-feeding animals the females are no doubt found on the pasturage more often than the males, for the reason that the females have to nourish both themselves and their young, whereas the males, which have themselves only to provide for, are contented with less food and inhabit chiefly more retired and less fertile regions; they are also shyer and are less easily shot and trapped. Regarding statistical data relating to the influence of nutrition on the production of boys, Breslau shows, from the figures of the Canton of Zurich, that with few exceptions, the years in which the price of corn was lowest were the years in which the production of boys was greatest, and vice versa—the exact opposite of the results obtained by Ploss from his examination of the figures relating to births and the price of provisions in Saxony.
Wappaeus contests the conclusions of Ploss even more vigorously, and adduces the statistics of Sweden in the 20–year period 1770 to 1790, in which period this kingdom repeatedly suffered from famine in consequence of failure of the crops, so that the births and deaths were largely affected. It appeared, however, that the more abundant or more scanty nutrition of the inhabitants of Sweden during this period had no marked influence upon the sexual ratio.
If scanty nutrition of the mother had, in fact, any influence upon the determination of the sex of the embryo in the direction alleged by Ploss, viz., so as to bring about the birth of a greater excess of boys, this influence should be manifested with exceptional clearness in the case of twins, for it is obvious that the nutriment that is insufficient for one embryo would be still scantier for two. Hence various statistical investigations have been undertaken to determine the sexual ratio in the case of twin births. Ploss found that in Saxony, in the case of 23,420 twin births, the sexual ratio was 106.7 boys to 100 girls; Moser gives the sexual ratio in the case of twin births as 106; Meckel von Hemsbach gives it as 105.4; Hecker, 116 and 122; Sickel, 112.3. Düsing combined the figures relating to twin births in various lying-in hospitals, published by Hecker, Sickel, Baillarger, Siebold, Elsässer, and Levy, respectively, and thus obtained a sexual ratio of 121.5 boys to 100 girls. This excess of boys is notably greater than among births in general.
But other statistical data are available which show a reversed condition, viz., that in the case of twin births the sexual ratio is lower than usual. According to von Frick’s collection of twin births in Prussia, the sexual ratio was 104.7 boys to 100 girls; whereas in the case of single births in the same country the sexual ratio was 106.35 to 100. Riecke, in Württemberg, in the case of 60 twin births found 58 boys and 62 girls. In the case of twin births observed by Braun, Chiari, and Späth, 94 in all, the children were in 64 of these of identical sexes, namely, in 30 instances boys, and in 34 instances girls. According to Breslau, in the case of twin births in the Canton Zurich, the sexual ratio was 104.1 to 100; whereas in the case of single births the sexual ratio was 106.2 to 100.
As regards triplets the reports of the sexual ratio vary from 111.76 : 100 (Meckel von Hemsbach) to 104.55 : 100 (Neefe).
It is obvious that the statistical data at present available regarding the sexual ratio in the case of multiple births are far too variable for it to be possible to base upon them any valid conclusions as to the influence of the nutritive condition of the mother upon the determination of the sex of the offspring. And taken as a whole the statistical data hitherto available do not enable us to infer with confidence that nutritive conditions, and more especially the nutritive state of the maternal organism, exercise any effect upon the determination of the sex of the offspring.
Another attempt at the utilization of statistics has been to ascertain whether the time of fertilization in relation to menstruation, (in the first days after the flow, or later in the intermenstrual interval) has any influence upon the determination of sex. The starting point in this investigation was the earlier view that sex depends upon the state of the ovum, and the belief that a very favourable state of ovum and sperm favours the production of the female sex. The ovum, after its discharge from the ovary, like the spermatozoon after its discharge from the testicle, tends sooner or later toward death, and the only thing that can save either from this ultimate fate, is for the two to unite to form a new organism. Precisely what moment in the history of the detached ovum is the most favourable, is a matter regarding which we have no exact information, but it is probable that at the moment of its discharge from the ruptured follicle, it is at the zenith of its vital powers. On this theory the determination of sex depends upon the period at which, after its liberation from the follicle, the ovum encounters a spermatozoon; the ovum which is fertilized early in its career becomes a female embryo; the ovum, on the other hand, which is not fertilized until it has become comparatively old, becomes a male embryo. But, as Hensen points out, a spermatozoon, according to its condition, may either fail sufficiently to fortify an ovum which itself is in good condition; or, on the other hand, a powerful spermatozoon may fortify an ovum of deficient vitality. But it is difficult to say precisely on what considerations the greater or less vitality of the spermatozoon depends—or, to speak more in accordance with the terms of the theory, we do not know exactly what makes it a good spermatozoon or the reverse. It may be “bad,” either because it has remained too long in the testicle or because it has been discharged too quickly, is too recently secreted; moreover, a long sojourn of the spermatozoon in the uterus will doubtless suffice to lower its vitality.
The Jews, more especially, whose religious ordinances forbid them to have sexual intercourse either during or shortly after menstruation, and among whom there is a great excess of male births, have been adduced as a proof of the thesis that sexual intercourse during the later part of the intermenstrual interval tends to favour the procreation of boys. In Leviticus xv. 19, we read: “And if a woman have an issue, and her issue in her flesh be blood, she shall be put apart seven days.” From the commentary in the Talmud it appears that these seven days are to be reckoned from the commencement of the flow. Statistical reports from various countries show that among the Jews there is a greater excess of male births than among the other inhabitants of the respective countries. The overplus of male births exhibited by the Jews varies from 1 to 15%, the difference probably depending on the fact that the number of instances under consideration is too small for uniform results to be possible. In Prussia, during the period 1820 to 1834, the sexual ratio among the Jewish births was 111 : 100; during the period 1849 to 1852 it was 106 : 100; in Hungary during the period 1835 to 1855 it was 117.1 : 100; in Sweden, 1851 to 1855, it was 108 : 100. Among illegitimate children of the Jewish community the sexual ratio was, in Austria, 123.9, in Prussia, 118.6.
Fürst, examining the cases in von Braun’s clinic, and making a statistical collection of the days of conception and of delivery, has endeavoured to prove that “there is an excess of boys when conception occurs during the period of post-menstrual anæmia.” His figures show, in fact, a very notable excess of boys in cases in which conception has occurred during the five days immediately following the cessation the menstrual flow; and an excess of girls when conception has occurred during the later part of the intermenstrual interval. Thus, in the former case the excess of boys is represented by the figures 37 : 12; in the latter case the excess of girls is represented by the figures 79 (girls) : 65 (boys). These figures are explained by Fürst on the theory that in the human species conception during the period of post-menstrual anæmia probably leads to an enormous excess of male conceptions (owing to the fact that the unfertilized ovum is badly nourished during the days just before conception); whereas in the later part of the intermenstrual interval the better nourishment of the ovum probably leads to the procreation of an excess of girls—hypotheses which are based on a quite inadequate number of instances. Fürst gives the following table:
| Number of Days Between Reputed End of Menstruation and Reputed Occurrence of Conception. | Number of boys born. | Number of girls born. | Boys and girls together. |
|---|---|---|---|
| 1 | 7 | 1 | 8 |
| 2 | 6 | 3 | 9 |
| 3 | 9 | 5 | 14 |
| 4 | 15 | 3 | 18 |
| 5 | 3 | 6 | 9 |
| 6 | 5 | 6 | 11 |
| 7 | 6 | 5 | 11 |
| 8 | 2 | 8 | 10 |
| 9 | 4 | 5 | 9 |
| 10 | 6 | 4 | 10 |
| 11 | 6 | 5 | 11 |
| 12 | 3 | 6 | 9 |
| 13 | 4 | 5 | 9 |
| 14 | 6 | 5 | 13 |
| 15 | 1 | 2 | 3 |
| 16 | 2 | 5 | 7 |
| 17 | 2 | 3 | 5 |
| 18 | 3 | 3 | |
| 19 | 1 | 3 | 4 |
| 20 | 1 | 2 | 2 |
| 21 | 1 | 1 | 2 |
| 22 | 4 | 1 | 5 |
| 23 | 1 | 1 | |
| 24 | 1 | 1 | |
| 25 | 2 | 2 | |
| 26 | 2 | 2 | |
| 27 | 1 | 1 | |
| 28 | 1 | 1 | 2 |
| 31 | 1 | 1 | |
| 102 | 91 | 193 | |