312 CHARLES HERRMAN 



Antitoxines, vaccines and convalescent sera have not been employed in a 

 sufficiently large number of patients to have a definite effect in reducing 

 the mortality. Preventive measures and improved hygiene have been of 

 undoubted value, but as Holt says they do not satisfactorily account for the 

 marked reduction. A very good illustration of the difference in resistance 

 to scarlet fever is furnished by Yoyoda (10) and his co-workers. Working 

 in Dairen in Manchuria, they compared the relative susceptibility of the 

 native Chinese and Japanese to the Dick toxin, and made a statistical study 

 of the relation of scarlet fever morbidity. The environmental conditions 

 were similar for both groups. Of 11,000 Japanese tested 37.3 per cent were 

 Dick positive, of 3500 Chinese only 19.4 per cent were positive. The 

 average annual morbidity from scarlet fever among the Japanese was 361 

 per 100,000 among the Chinese only 8 per 100,000, that is the Japanese 

 were 45 times as susceptible as the Chinese. The Chinese especially those 

 of northern China have suffered severely from famine and disease, and have 

 therefore been subjected to rigid selective elimination so that only the more 

 resistant lines have survived. Of these the hardier and more adventurous 

 seeking more fertile land have migrated to Manchuria. In Hawaii also 

 striking differences between these two groups have been noted. Both have 

 a high birth rate, but among the Japanese the death rate is high, and the 

 infant mortality rate very high, while among the Chinese the death rate is 

 low, and the infant mortality very low. 



SUMMARY 



1. Although preventive measures and improved hygiene have been 

 important factors in the decrease in the mortality in infancy and childhood, 

 they do not fully account for the remarkable reduction. 



2. In addition there has been a selective elimination of the less resistant 

 strains which are thus prevented from becoming parents. In large centers 

 of population, on account of the congestion, contact infection and selective 

 elimination takes place at an earlier age. 



3. The relative number of deaths in male and female infants and children, 

 is a fairly reliable index of the amount of selective elimination. The greater 

 the ratio of male to female deaths the greater the selective elimination. 

 As the mortality in infancy and childhood decreases, the sex ratio increases. 

 The respiratory infections as causes of death have a more selective action 

 than the digestive disorders, therefore the sex ratio is higher in winter than 

 in summer. 



4. The reduction in the total mortality in New York City, has been due 

 chiefly to the reduction in the mortality in infancy and childhood. This 



