NATURAL DEATH, PUBLIC HEALTH 237 



laissez-faire policy would be better, or that public health 

 efforts have not been enormously valuable in connection 

 with typhoid fever and diphtheria. My purpose is quite 

 other, being solely a desire to emphasize two things, viz: 

 1. That the trend of human mortality in time is an 



too 



9O 



SO 

 70 



60 

 -50 



40 



30 



^o 



to 



DIPHTHERIA 



1898 99 19OO Ol 



0^ 03 04 O5 06 O7 08 09 



YEAR 



10 II 12 



Fia. 56. Like figure 55, but for diphtheria and croup. 



extraordinarily complex biological phenomenon, in 

 which many factors besides the best efforts of health 

 officials are involved. 



2. That for many causes of death a vast lot needs to 

 be added to our knowledge of etiology, in the broadest 

 sense, before really efficient control can be hoped for. 

 This knowledge can come only through scientific investi- 



