SEX-RATIO OF NEW-BORN INFANTS, AS AN INDEX OF 



VITALITY 



V. BUNAK 



Moscow, U. S. S. R. 



1. Starting point in the analysis of the various Sex-Ratios of new-born 

 infants (SRi) is the thesis formulated in its clear form, firstly by Rauber 

 (1900) : the greater the number of abortions and stillbirths in a given group, 

 the lesser the predominance of boys among new-born infants. 



2. This thesis is based on the well known fact of greater mortality of boys 

 in the intrauterine period, the younger the foetus the greater the mortality. 

 The true SR (SR of all embryos at an early period) must therefore be much 

 higher than it is at birth (104-106). 



3. The exact value of the true SR can only be determined approximately. 

 According to a detailed table by G. von Mayr the SR of stillborn infants 

 which undoubtedly include a great number of immature foetuses from seven 

 to nine months varies in different countries from 120 to 140 and gives an 

 average of about 130. In miscarriages of from four to seven months which 

 except in rare cases are undoubtedly involuntary and must be considered as 

 cases of mortality, the SR averages 160 -s- 156 according to Budapest (Auer- 

 bach) statistics, 162 in accordance with a compilation from all available 

 sources drawn up by Prinzing. For the younger embryos no reliable data 

 is at hand because during the first seven weeks the sex of an embryo is un- 

 determined. At the age of eight to eleven weeks sex may be determined 

 microscopically and from the twelfth week macroscopically, although only in 

 especially favourable cases, most embryos being seriously damaged by the 

 abortive operation. My own, as yet insufficient material concerning the 

 embryos of third months obtained from voluntary abortions which are the 

 only ones able to give an idea concerning the true SR does not coincide with 

 the high SR given by Berthillon (400) and Tshuprov (700). But the figure 

 of Auerbach (124) is perhaps too low. The estimation of the SR being so 

 uncertain we can hardly lay much stress upon the various theories concern- 

 ing the numerical inequality of sexes (the theory of selective fertilization, 

 etc.), the more so as there are many mammals where the male sex does not 

 predominate at birth, or is even less numerous. 



4. The knowledge of the true SR is of great significance for the whole 



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