SELECTIVE ELIMINATION 301 



method of determining susceptibility. The Hirszfelds (3) have shown that 

 when both parents have a positive reaction, that is are susceptible to diph- 

 theria, almost all the children have a positive reaction; when both parents 

 have a negative reaction, about one-third of the children have a positive 

 reaction, two-thirds a negative reaction; and when one parent is positive, 

 the other negative, one-half of the children have a positive reaction. The 

 experimental work of Webster (4) on laboratory animals has also demon- 

 strated the hereditary factors in resistance to infection, and the important 

 role of selective elimination. "Five hundred female and one hundred male 

 mice of The Rockefeller Institute strain were mated, one male to five fe- 

 males. When the young were weaned, the six hundred parents were given 

 intrastomachally three million enteritidis mouse typhoid bacilli. In cases 

 in which both parents died within ten days after infection and in which, on 

 the other hand, both parents survived sixty days, the respective litters from 



susceptible and resistant parents were saved for further breeding Thus 



far, five lines of susceptible mice and six lines of resistant mice have been 

 selected. The susceptible lines show approximately 95 per cent mortality 

 within fifteen days after exposure, the control group shows 35 to 40 per cent, 

 and the resistant lines show approximately 5 per cent mortality over the 

 sixty-day period of observation." 



In infants a very rigid selective elimination process takes place from the 

 time of conception (chart 1). A large number of fetuses do not survive the 

 first few months of intrauterine life, of the remainder many are still born or 

 succumb shortly after birth, unable to meet even the first tests of extrau- 

 terine life. Many of those who survive the neonatal period are constitu- 

 tionally inferior, afflicted with the so-called exudative, lymphatic or neuro- 

 pathic diathesis, and die as the result of comparative mild infections. At 

 the second international eugenic congress in 1921, Holmes and Goff (5) 

 demonstrated that in intrauterine life and in infancy the male is the weaker 

 sex, and that this is due to biologic factors. It may be stated as a general 

 rule that the greater the selective action the greater will be the ratio of male 

 to female deaths, and as the infant mortality diminishes the ratio of male 

 to female deaths tends to increase, because the selective action becomes in- 

 creasingly prominent. In England and Wales (6) from 1841 to 1850 the 

 infant mortality was 153 per 1000 births, with a ratio of 122 male to 100 fe- 

 male deaths, in 1926 with an infant mortality of 70, the ratio had risen to 

 130 male to 100 female deaths. New York City has now an infant mortal- 

 ity rate of 56 per 1000 births with a ratio of 134 to 100, and under five years 

 the ratio is 125 to 100 female deaths, indicating that at that period the selec- 

 tive action is still marked. As Bakwin (6) states during the summer the 



