Factors Influencing the Human Sex-ratio. 129 



existed, their conclusions, based as they are on statistics leaving 

 these births out of consideration, would be unaltered. 



A tabulation of the percentage of still births occurring among 

 the cases studied at the Sloane hospital gives the following result: 





Total Cases. 



No. of Still 

 Births or 

 Abortions. 



Per Cent, of 

 Stil Births or 

 Abortions. 



Difference. 



Difference 

 P. E. 



Pure matings 



Hybrid matings . . . 



5-753 

 1.305 



355 

 52 



6.17 ±.21 

 3-98 ±.36 



2.19 ±.41 | 



5-34 



In the material studied, therefore, there appears to be a sig- 

 nificant excess of still births in the pure matings as compared 

 with the hybrid matings. Although the Pearls appear to con- 

 sider this as a result unlikely to be obtained, it would seem that 

 did still births depend upon a recessive factor or factors peculiar 

 to certain races, there would be less chance for two gametes 

 containing such factors to meet in a hybrid mating than in a 

 mating within the race possessing the factor or factors in question. 



Inasmuch as many embryos may reach birth although infected 

 with syphilis it is likely that biological factors are involved in most 

 if not all cases of still births resulting from syphilis. Such factors 

 would determine susceptibility of the embryo in much the same 

 manner as other biological factors produce strains or families with 

 susceptibility to lung infections or some other weakness. It 

 should be noted further that the results have proved significant 

 in spite of certain rare unavoidable errors of classification, by 

 which " hybrid " matings may be classed as " pure " and vice versa. 

 Errors of this sort would tend to mask and not aid the results 

 obtained. 



The better record as regards still births is merely another way 

 of stating that the Fi racial hybrids in man would tend to show 

 the vigor which has frequently been found to characterize racial 

 hybrids in other mammals, such as rats, mice, and guinea-pigs. 

 Such first generation hybrids would possess the factor complexes 

 characterizing their respective races and would benefit by the 

 summed up effects of all dominant factors of both races which 

 might make for normal growth or development. That genetic 

 factors which result in still birth are recessive, if they exist at 



