308 HUMAN BIOLOGY 



of months is small because the weather conditions are 

 extreme, the general degree of regularity in Figure 2 is high. 

 The optimum temperature is evidently 64 to 6^° which is 

 close to that which we found in New York City. At that 

 temperature the best condition of humidity appears to be 

 80 to 85 per cent. Thus the main climatic optimum for the 

 cities of France and Italy is an average monthly tempera- 

 ture of 64° to 65° and an average relative humidity of 85 to 

 90 per cent. 



As one departs from the optimum in any direction, the 

 death rate increases, slowly along the hne indicating the 

 optimum temperature, most rapidly where the temperature 

 and humidity both become unfavorable. Low temperature 

 is bad even if the air is moist, but very bad if the air is dry. 

 The worst figure on the chmograph is an excess of 42.5 per 

 cent with a humidity of §s to 60 per cent and a temperature 

 of 40°. Under the very hot, dry conditions shown in the 

 upper left hand corner of Figure 2, the death rate Hkewise 

 rises very high, being 31.6 per cent above normal. Under 

 hot moist conditions the rate might be still higher, but 

 France and Italy, with their dry summers except in the 

 cool north, are free from such conditions. 



Turn now to Figure 3, representing 921,000 deaths from 

 non-contagious diseases among white people in the cities 

 of the eastern United States from 19 12 to 1915. It is hke 

 Figure 2 except that the numbers have been omitted, the 

 isopleths have been smoothed to remove irregularities, 

 and shading has been added so that good conditions are 

 dark and bad conditions hght. The general aspect of the 

 chmograph is almost identical with that of Figure 2. The 

 best health and fewest deaths occur with a temperature of 

 approximately 6^° and a relative humidity of 80 to 85 per 

 cent. Poor health and many deaths prevail when the weather 

 is hot and dry and especially when it is cold and dry. 



Many other investigations give similar results. Under 

 most conditions fairly moist air is better than dry, and this 

 is true even when the optimum temperature prevails. In 

 both very hot and very cold weather, however, extreme 

 humidity is less favorable than more moderate conditions. 

 In cold weather this must be partly due to the exposure 



