THE INHERITANCE OF DURATION 161 



How great and deep is the significance of the facts 

 shown in Table 16 may best be brought home to the mind 

 by means of a comparison. Suppose this question to 

 be asked: by how great an amount would the average 

 expectation of life at birth (which in a stable population 

 is the same thing as the mean duration of life) be increased 

 if all the reasonably preventable deaths were prevented? 

 If, say 75 per cent, of all the deaths from pulmonary tuber- 

 culosis did not occur; if 40 per cent, of the deaths from 

 Bright 's disease were prevented; and, in general, if 

 all that medicine and hygiene knows today were put 

 into reasonably effective operation, and nobody died 

 except when and from such causes as coxdd in no 

 way be influenced by what medical science, good envi- 

 ronment, etc., have to offer: by how much then would 

 the expectation of life be greater than it now is? We 

 have seen that to have one's parents live to 80 or over 

 increases the expectation of life 20 years, as compared 

 with that of persons whose parents die under 60 years of 

 age. By how much more would the expectation of life 

 be extended if all reasonably preventable deaths were 

 prevented? 



A thorough and critical answer to this question is 

 afforded by an investigation of Forsyth 's» conducted 

 along the most exact and approved actuarial lines. 

 Some years ago, Professor Irving Fisher sent a list of 

 some 90 diseases to a group of the most prominent medi- 

 cal authorities in this country, and asked them to desig- 

 nate what percentage of the deaths due to each disease 

 they considered preventable. The results of this inquiry 

 were tabulated in an extremely conservative manner, 

 with the result set forth in Table 16a, which is copied 

 from Forsyth's paper(pp. 762-763). 



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