60 WORLD-POWER AND EVOLUTION 



and the percentages by which the deaths departed from the normal 

 for the year in question. 



Deaths in New York City during July and March, 1900-1915 

 July March 



In July the higher the temperature the higher the deathrate. 

 The difference between the hottest and the coolest years amounts 

 to 28.9 per cent. In March the opposite is the case, for the 

 warmest months had 13.9 per cent less deaths than the coldest. 

 In both cases notice how regularly the deathrate declines as the 

 temperature becomes more favorable. Under ordinary conditions 

 no differences in food or drink ever cause one tenth as much 

 variation. Neither do epidemics cause any such variations in the 

 deathrate. Among the epidemic diseases of the United States 

 pneumonia, diphtheria, and influenza cause much the largest 

 number of deaths, provided we omit tuberculosis. Tuberculosis, 

 however, acts very slowly so that the deathrate from this cause, 

 which was 9.5 per cent of the total in 1915, shows only very slight 

 variations from year to year. Pneumonia, although infectious, 

 depends almost wholly upon the weather conditions. It caused 

 6.1 per cent of all the deaths in 1915. Influenza and diphtheria 

 each accounted for only 1.2 per cent of the total deaths in 1915. 

 Yet that was an uncommonly bad year for influenza. Even when 

 these epidemic diseases are at their worst none of them causes a 

 variation of more than 2 or 3 per cent of the deaths in the country 

 as a whole. 



