202 



BIOLOGY OF DEATH 



environmental conditions, than do normal non-sterile 

 indeed germ-laden flies. This result is of great inter- 

 est and significance. It emphasizes in a direct experi- 

 mental manner that in a broad biological sense bacteria 

 play but an essentially accidental role in determining 

 length of the span of life in comparison with the influence 

 of heredity. 



POVERTY AND DURATION OF LIFE 



But we must take care lest we seem to convey the 

 impression that no sort of environmental influence can 

 affect the average duration of life. Such a conclusion 

 would be manifestly absurd. Common sense tells us 



PERSONAL PROPERTY TAX IN PARIS 191 1 -1913 



I 1 PAYING H 



i 



% 



90 - 

 60 

 70 

 60 

 50 

 AO 

 30 

 ZO 



10 

 O 



8 16 9 



I 17 6 10 2 3 5 4 1Z 14 15 18 II 13 19 ZO 



ARRONDISSLMENTS 



i n in N 



CLASSES OF 



PARS 



FIG. 50. Distribution of poverty in Paris (1911-13) as indicated by exemption from personal 



property tax. (After Hersch). 



that environmental conditions in general can, and under 

 some circumstances, do exert a marked influence upon 

 expectation of life. A recent study of great interest and 

 suggestiveness, if perhaps some lack of critical sound- 

 ness, by the eminent Swiss statistician, Hersch, may 

 be cited in this connection. Hersch became interested 

 in the relation of poverty to mortality. He gathered 



