SELECTIVE ELIMINATION 313 



has resulted in an increased proportion of adults in the population, with a 

 resulting increase in the number of deaths from the diseases peculiar to 

 middle and old age. 



5. The most important causes of death may be conveniently divided 

 into three groups, (a) Diseases of middle and old age, in which there is 

 little selective action, and little or no reduction in the death rates, (b) 

 Diseases of children as well as adults, in which there is moderate selective 

 action, and some reduction in the death rates, (c) Diseases almost exclu- 

 sively of infancy and childhood in which there is a marked selective action, 

 and in which there is a great reduction in the death rates. 



6. As the mortality in infancy and childhood decreases, the infections 

 of the respiratory system become increasingly important, and as the eti- 

 ological factors are to a great extent beyond our control, measles and epi- 

 demic catarrh (influenza) with their complicating pneumonia, are the chief 

 agents in the selective elimination process. 



7. In different groups living under similar environmental conditions, 

 there may be marked differences in the adequacy of their immunologic 

 reactions, which in turn are dependent upon the amount of selective elimina- 

 tion of non-resistant strains that has previously occurred. 



REFERENCES 



(1) Holt: J. A. M. A., October 6, 1923. 



(2) Herrman: The Nation's Health, August, 1924. 



(3) Hirszfeld: Ztschr. f. Hygiene, 104, 1925. 



(4) Webster: Science, 75, 445, 1932. 



(5) Holmes and Goff: Eugenics in Race and State, p. 233. 



(6) Bakwin: Am. Jour. Dis. Child., 36, 182, 1928. 



(7) Fishberg: Tuberculosis among Jews. 



(8) Boyd: Textbook of Surgical Pathology. 



(9) Crampton: Science, 55, 90, 1922. 



(10) Yoyoda: Jour. Infect. Dis., 46, 186, 1930. 



