SEX-INCIDENCE IN ABORTIONS. 185 



perishing during the period from the fifth to the seventh month is relatively, not 

 absolutely, equal. At any rate, it is apparent that during the middle third of 

 intrauterine development the excess of male abortions is much lower than at 

 the beginning and at the end of pregnancy. 



In order to make use of the above citations and figures in computing the 

 primary sex-ratio, rough and approximately average values must first be estab- 

 lished. The following appear to be most probable: For each 100 living-born, with 

 a sex-ratio of 105.5, there occur in the eighth to the tenth month 4 still-births with 

 a sex ratio of 130; in the fifth to the seventh month 7 abortions with a sex-ratio 

 of 106; in the fourth month 2 abortions with a sex-ratio of 120; and from con- 

 ception to the end of the third month 15 abortions with a sex-ratio of 125. This 

 makes altogether 28 abortions and still-births to every 100 living-born; i.e., 100 

 living-born to every 128 fertilized ova. 1 The primary sex-ratio found from these 

 averages by simple mathematical operations is 108.74. The writer's last calcula- 

 tion of the primary sex-ratio (1918) resulted in 108.47. The very small increase 

 in the corresponding value of the present study serves as a confirmation of the 

 previous finding. The sex-ratio at conception was estimated by Bernoulli as 108.2. 

 Slightly higher (108.7) is the ratio computed by Jendrassik (1911) from statistics 

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

 author. Lenhossek (1903) estimates the primary sex-ratio as 111, 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 will become more exact only when 

 based upon more extensive, careful statistics, must be accepted cum grano salis, 

 it may nevertheless be stated with certainty that more males (not exceeding 

 10 per cent) are conceived; that at certain periods of pregnancy the relative mor- 

 tality of males exceeds that of females by as much as one fourth or more; and that 

 this, in connection with the very high intrauterine mortality, especially at the 

 beginning of pregnancy, serves to lower the primary sex-ratio considerably through- 

 out prenatal life. 



DETERMINATION AND CHANGES OF THE PRIMARY SEX-RATIO. 



The question now arises as to what determines the sexes and their unequal 

 distribution at conception. Its discussion dates back into antiquity; since Aris- 

 totle, philosophers and physiologists searched in vain for the key to this problem. 

 The most fantastic theories were advanced, one of the oldest being that sex is 

 correlated respectively with the right or left ovary or testicle (Hippocrates, Galen). 

 In recent times much work has been done in trying to solve this problem. Among 

 the most interesting theories stands the idea of the possibility of two distinct 

 varieties of spermatozoa. Wilson (1905) distinguishes between male-producing 

 and female-producing spermatozoa. This might lead to an unequal distribution 

 of sexes at conception. Morgan (1913) suggested that it may be due to a difference 



1 The relative number of fertilized ova, estimated by Rauber to be 100 to 76 living-born or, calculated as above, 

 131.6 to 100 living-born, is somewhat larger than that obtained by the author. 



