PREVENTIVE MEDICINE—BOYD oL5 
the conditions we are considering are most active as causes of 
death among the ages below 30. Their elimination will, of course, 
permit a larger proportion of individuals to survive to ages be- 
yond 380, and as the change takes place the number of deaths above 
30 will slowly increase, proportionate to the decrease in the deaths 
below 30. (3) The conditions which are operative as causes of 
death at the age periods beyond 30 other than those of our par- 
ticular groups will gradually be found to be responsible for an 
increasingly greater number of deaths. This state of affairs is not 
necessarily alarming, but rather is encouraging, as indicating that 
a larger proportion of individuals are permitted to survive to 
middle life and older periods. This is in our opinion, the most 
rational explanation of the increases which have been observed in 
the mortality from carcinoma and cardio-renal disease. ‘The com- 
pletion of this cycle of transformation will probably leave us with 
a crude death rate from all causes very nearly the same as before 
the days of even the most feeble preventive work. The important 
difference will be in the age distribution of the deaths. Instead 
of the many dying young, the majority will survive to middle 
life or old age. The individual will have a better chance of liv- 
ing what may be said to be a life of “ normal” duration. 
New York City furnishes us with a concrete example of. the 
influence that improved hygiene and sanitation exerts in prolonging 
human life. In 1882 Dr. J. S. Billings prepared a life table for 
New York City based upon the mortality experience for the years 
1879, 1880, and 1881. At that time a male child five years of 
age could expect to live 39.7 years longer, and a female child 42.8 
years longer. In 1913 a similar table was prepared based upon the 
experience of the years 1909, 1910, and 1911. Males at the age of 
five have an expectation of 50.1 further years of life, and females 
an expectation of 53.8 years. Thus in this period of 30 years the 
expectation of life for males at the age of five years has increased 
by 10.4 years and that of females by 11 years. The life tables 
referred to are reproduced in Table II. This increase in the ex- 
pectation of life is observed at all ages up to 35, while at all ages 
above 43 is a constantly increasing diminution in the duration of 
life. This change in the expectation of life in New York is justly 
referable to improved hygiene and sanitation, as New York City 
was one of the first cities in the country to organize an efficient 
health department, which has since been maintained on a high plane 
of efficiency. 
(6) Unhealthful regions of the earth will be made habitable, 
consequently human overcrowding will be relieved, and more of the 
earth’s treasures will be available for mankind. 
