SEX-RATIO OF NEW-BORN INFANTS 433 



matings, etc., which give the higher SRi. In the Russian population for 

 example many rural districts show a lower SRi than the urban population 

 does, contrary to what is known in Western Europe: 1 The northern region: 

 rural district 106, urban 110; Black Soil Region 106 and 108; the Viatka 

 Section 105 and 108; Republic of White Russia 106 and 109. Many regions 

 register no difference in SRi between urban and rural populations. This fact 

 is fully comprehensible if we bear in mind that the percentage of natural 

 abortions is higher in many rural communities than in the urban ones. Per- 

 haps this is due to the unfavourable influence of the frequent pregnancies of 

 women and lack of care. Bogaslovsky's statistics confirm this supposition. 



8. All these facts enable us to understand the SRi as a suitable measure of 

 prenatal mortality, perhaps not very exact, but nevertheless very useful, 

 since all direct research in this field is inevitably very unsatisfactory. In 

 other words we may use the SRi as an index of prenatal vitality: the greater 

 the SRi the lower the prenatal mortality. 



9. A given value of SRi may have an entirely different meaning. An in- 

 dex below the average (104-106) can be provoked: (1) by the reproductive 

 system, such for instance as frequent pregnancies and therefore numerous 

 abortions which are very characteristic for many groups of high natality: 

 (2) by pathological conditions such as syphilis which increases prenatal mor- 

 tality; (3) by physiological predisposition, which we may confirm when the 

 two former factors are excluded. Analogous types can be established 

 among groups of high SRi. 



A constitutional type of lower prenatal vitality seems to me to be character- 

 istic of many North-Siberian native tribes although there are certain tribes 

 which register a very high SR. In general a low SRi is characteristic of 

 tribes which show no increase in number of recent years. Although the data 

 are not extensive, they embrace the greater part of the given tribe 2 (table 1). 



10. The relation between prenatal and postnatal infant mortality is not 

 always the same. Since this involves many complex factors, a calculation 

 of the coefficient of correlation between the SRi and the index of infant mor- 

 tality is useless. Combining the extreme values of the indices we may dis- 

 tinguish two types: if a low SRi is accompanied by a low index of infant 

 mortality we may conclude that the prenatal mortality is especially selec- 

 tive and by eliminating weaker foetuses it decreases later infant mortality. 

 But I was unable to find an example of this kind in the available statistics. 



1 Administration Centrale de Statistique de l'U. R. S. S. Mouvementde la Population 

 en 1926. 



2 Administration Statistique Centrale. Recensement des Menages du Nord Polaire 

 de l'URSS 1926-27. 



