STUDIES IN THE SEX-RATIO IN MAN. 267 



parents are of different racial stocks. The well-known assertion 

 that sex-ratio rises after wars, has evoked various attempts at 

 explanation. The following few examples are given: Ploss ('58, 

 '61) ascribes it to malnutrition of the mothers. Berner ('83) 

 believes it to be due to the diminished concurrence which follows 

 wars and which brings about an increased prosperity. Diising 

 sees the cause in the increased sexual demands upon the male, 

 which also is said to increase the sex-ratio in polygamy. Ac- 

 cording to Newcomb, following the Civil War no increase in 

 sex-ratio was observed. In the cases where a difference was con- 

 firmed it was so slight 1 as not to exceed the normal variations as 

 shown by Lehr ('89), Carlberg and others, and is to be considered 

 as such. Variations of sex-ratio have been determined not only 

 for individual years and for groups of years, but also for the 

 seasons. According to Goehlert ('89) in autumn and winter 

 relatively few conceptions take place, but a higher percentage of 

 these are male. 



CHANGES IN THE SECONDARY SEX-RATIO. 



The primary sex-ratio, as shown above, becomes transformed 

 by an unequal intrauterine mortality of the two sexes into a 

 different secondary sex-ratio. The greater mortality of males 

 during certain periods of prenatal life is explained by Carvallo 

 as follows: "les garcons sont plus fragiles." Auerbach also con- 

 siders the male foetus less resistant. Grassl ('12) finds an expla- 

 nation for the difference in the viability of the germ plasma. 

 Jendrassik speaks of hereditary reduction of vitality among the 

 excess of males. Rauber explains the greater mortality of males 

 by the greater demands of the larger foetuses upon the mother, 

 the latter not always being able to meet them ; the production of 

 a female does not require as much from the mother. Lillie ('17) 

 offers the suggestion that the greater mortality among male 

 foetuses is a result of disturbance of the equilibrium that protects 

 the male from the sex-hormones of the mother. It seems prob- 

 able that this is the case, especially in the first part of pregnancy. 



1 For example Henneberg's ('97) statistics show that in Holstein between 1835 

 and 1845 the sex-ratio was 105.76, after the period of war from 1846 to 1853 it wag 

 106.67. 



