SEX-INCIDENCE IN ABORTIONS. 187 



definite is known concerning a correlation between the age of the parents and sex 

 determination; in fact, such a correlation is hardly to be expected. 



Pearl (1908), in a very careful study, demonstrated that there are more males 

 produced when the parents are of different racial stock. The same effect of hy- 

 bridization on the sex-ratio has been found by King (1911) for rats and by Guyer 

 (1903) for birds. The well-known assertion that the sex-ratio rises after wars 

 has evoked various attempts at explanation. The following few examples show 

 best how little the different authors agree on this improbable relation. Ploss 

 (1858, 1861) ascribes it to malnutrition of the mothers. Berner (1883) believes 

 it to be due to the decreased competition which follows wars and which brings 

 about an increased prosperity. Busing sees the cause in the increased sexual 

 demands upon the male, which is also said to increase the sex-ratio in polygamy. 

 According to Newcomb, following the American Civil War of 1861-65 no increase 

 in sex-ratio was observed. Nichols found no effect of war upon the sex-ratio in 

 France from 1806 to 1872. On the other hand, Henneberg (1897) claims to have 

 found such an influence; he reported that in Holstein, between 1835 and 1845, 

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

 was 106.67. In the few cases where such a difference was confirmed, it was so 

 slight as not to exceed the normal variations of the secondary sex-ratio (it is in 

 the latter that any difference would be found) and therefore is to be considered 

 as such. These natural variations were shown by Lehr (1889), Carlberg, Nichols, 

 and others; they may be very considerable, as reported by von Winckel (1903), 

 according to whom the sex-ratio of new-born in Berlin showed extremes in a 

 period of 100 years of 104.79 and 100.64. Variations of sex-ratio have been de- 

 termined not only for individual years and groups of years, but also for the seasons. 

 According to Goehlert (1889), in autumn and winter relatively few conceptions 

 take place, but of these a higher percentage is male. The same conclusion was 

 reached by Sormani (1883). Inasmuch as the studies of these authors were based 

 upon statistics of births, without consideration of the relative frequency of abor- 

 tions, their conclusions in regard to the sex-ratio at conception must be treated 

 with caution. 



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 ratio, and it is 

 obvious, from a mathematical consideration, that the greater the proportion of 

 abortions and still-births the lower will be the sex-ratio of living-born. Attempts 

 have been made by a number of authors to explain the great mortality of males 

 during certain periods of prenatal life. Carvallo simply says "les garcons sont plus 

 fragiles"; Auerbach, also, considers the male fetus less resistant. Grassl (1912) 

 gives as an explanation the supposition of a difference in the viability of the germ 

 plasma. Jendrassik speaks of hereditary reduction of vitality among the excess 

 of males. Ewart (1918) suggested that "it is possible here, of course, we have 

 no data that the female conception may graft itself on the lining membrane of 



