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THE AMERICAN NATURALIST [Vol. LV 



tion as is occupied now by the human life table curve. 

 Put in another way, what appears to have happened is 

 that, as compared with DrosopJiila, more human beings 

 are able to live through middle life, but at the expense of 

 those who, if the mortality law was the same as in 

 DrosopJiila, would live to extremely advanced old ages. 

 As a matter purely of speculation in the present stage of 

 our knowledge, it may be suggested that the DrosopJiila 



L curves represent more nearly the normal, fundamental, 

 biological law of mortality, and that the human curve has 

 been warped from this form as a result of those activities 

 which may be comprised under the terms public health 

 and sanitation. It is to be understood that at present we 

 offer this merely as a suggestion and in no way as a 

 settled conclusion. It is, however, clear that the effect 

 which we should expect these activities to have upon the 

 form of the L line is exactly of the sort which makes the 

 human curve different from the DrosopJiila in fact. 

 In this connection Fig. 5 is of interest and significance. 



