184 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



more hypotheses, bearing upon the determination of sex, have been brought 

 forward. The Bofacker-Sadler law (Hofacker, 1828; Sadler, 1830) is well 

 known, as follows: [f the lather be older than the mother, more boys than 

 girls will be born ; if the parents be of equal age, slightly more girls than 

 boys ; if the mother be older than the father, the probability of girls is still 

 greater. Since the promulgation of this so-called law facts for and against it 

 have been brought forward, but the balance of evidence seems to be in favor 

 of us truth. Thury in L863 claimed that the degree of "ripeness" of the 

 ovum is the determining factor — the female resulting from the less ripe ovum, 

 hence the earlier after its liberation the egg is fertilized, the greater is the 

 tendency to the production of a female : the later the fertilization, the greater 

 the probability of a male. While it is not at all clear in what the " ripeness" 

 or "unripeness" of an ovum consists, breeders have made use of this prin- 

 ciple apparently with success — offspring conceived at the beginning of " heat " 

 seem to be more usually females. Likewise, it is frequently believed that in 

 human beings conceptions immediately after menstruation produce a larger 

 proportion of females than later conceptions. Schenk 1 also bases his view- 

 on the condition of ripeness of the ovum. He regards the presence of sugar 

 in the urine of the pregnant woman as evidence of incomplete metabolism 

 in the body, thus of incomplete nutrition or unripeness of the ovum, and 

 hence of tendency toward femaleness in the offspring. By means of a highly 

 nitrogenous diet, which eliminates the sugar from the urine and increases the 

 proportion of reducing substances, he claims to make the metabolism more 

 complete, to insure a riper ovum, and hence to make it probable that the 

 offspring will be a male. Schenk's reasoning is excessively hypothetical, and 

 his present facts are too few to substantiate his claims. Diising 2 accepts 

 Thury's view and extends it to the male element — the younger the spermato- 

 zoon the greater the tendency toward the production of males. Hence among 

 animals the scarcity of one sex leads to the more frequent exercise of its 

 reproductive function, the employment of younger germ-cells, and therefore 

 the relative increase of that sex. Further, the nearer a parent is to the 

 height of his reproductive capacity the less will be the probability of trans- 

 mitting his own sex to the offspring. Nutrition seems to have some obscure 

 relation to the question of sex. Thus, by feeding tadpoles with highly 

 nutritions flesh Yung ; increased the percentage of females from 56 to 92. 

 Mrs. Treat 4 showed that the butterflies of well-fed caterpillars became 

 females, those of starved caterpillars males. Statistics among mammals and 

 human beings indicate that the proportion of male to female offspring varies 

 inversely with the nutrition of the parents, especially of the mother. Thus, 



1 I.. Schenk : Einflusz auf das Oeschlechtverhdltniss, Magdeburg, 1898. Authorized transla- 

 tion: The Determination of Sex, London, L898. 



'-' K. Diising: Jenaische Zeitschrift fur Natunrisscnschnft, 1 SS:i, xvi., and 18S4, xvii.; also 

 published separately, Die Regulierung des GeschlectverhaUnisses bei der Vermehruna der Menschen, 

 Tiere und Pflanzen, Jena, 1884. 



E. Yung: Comptes rendus de P academic des science*, Paris, INN], xcii. 



1 Mrs. Mary Treat: The American Naturalist, 1S7I!, vii. 



