STUDIES IN THE SEX-RATIO IN MAN. 265 



From this, x or the primary sex-ratio is found to be 108.47. 

 The relative number of conceptions was estimated by Rauber to 

 be 100 to 76 living born or calculated as above 131.6 to 100 living 

 born. This number is somewhat larger than that obtained by 

 the author, namely 127. The sex-ratio of conceptions was 

 estimated by Bernoulli as 108.2. Slightly higher (108.7) ' ls the 

 ratio computed by Jendrassik ('n) from statistics collected by 

 Bodio. Both these figures are strikingly similar to that of the 

 author, namely 108.47. Lenhossek ('03) estimates the primary 

 sex-ratio as in ; Auerbach as 116.4 but the latter believes that it 

 would reach at least 125 if corrections were made. 



Even if these approximate averages, which become constant 

 only when based upon extensive material, must be accepted 

 cum grano salis, it may nevertheless be stated with certainty that 

 more males (probably not more than 10 per cent.) are conceived, 

 and that at certain periods of pregnancy the relative mortality 

 of males exceeds that of females by as much as one fourth. 



DETERMINATION OF AND CHANGES IN THE PRIMARY SEX-RATIO. 



Now arises the question as to what determines this unequal 

 distribution of sexes at conception. Its discussion dates back 

 into antiquity, Hippocrates and Galen asserting that males 

 originated from the right testis or the right ovary, females from 

 the left. It has been proved that this theory is untenable; how- 

 ever, the idea of the possibility of two distinct varieties of sper- 

 matozoa was again revived in more recent times. Wilson ( '05) 

 distinguishes male-producing and female-producing spermatozoa. 

 This might lead to an unequal distribution of sexes at conception. 

 Morgan suggests that it may be due to a difference in the rate of 

 travel of the two types of sperm, or that a disease process, or a 

 factor such as alcoholism, might affect one type to a greater 

 degree than the other. Hertwig ('12) attributes sex-determi- 

 nation to the ovum or the degree of its maturation, an advanced 

 stage of maturation producing males. In this way he attempts 

 to explain the difference in sex-ratio according to social class. 

 Thury ( '63) had proposed the idea that ova which are fertilized 

 late may produce more males. Thus he explained the high sex- 

 ratio among Jews, who, on religious grounds refrain from inter- 



