CLIMATE AND HEALTH 71 



Japan, Russia, Scotland, Austria, and Germany. In a word, the 

 human race seems to have the best health when the average tem- 

 perature for day and night together is 64°F, that is, when the 

 thermometer rises to about 70° at midday, and drops to perhaps 

 55° at night. One would suppose that the Swedes of the far 

 north would have become wonted to a temperature colder than 

 that which is best for the Sicilians of the sunny south, but such 

 is not the case. Even the dusky American negroes, whose ances- 

 tors have lived for unnumbered ages in the tropical heat of Africa 

 and who still live where it is fairly warm, are at their best in a 

 temperature scarcely higher than that which is most favorable 

 for the blond Finns under the shadow of the Arctic Circle. In 

 fact, the poor Finns appear never to have a month warm enough 

 to put them at their best physically. Their deathrate keeps 

 declining as the temperature goes up, but might go still lower if 

 the summer were a little warmer. 



Thus far we have made no allowance for contagious diseases 

 except in Figures 18 and 19. This makes no difference, however, 

 for these two climographs are essentially the same as the others. 

 Moreover, I have prepared the climograph for the deaths from 

 contagious diseases which occurred in the same years and in the 

 same places as the deaths from non-contagious diseases used in 

 preparing Figure 18. This climograph is as regular as the 

 others. It differs from them in only two respects : First, a 

 departure from the optimum has a more pronounced effect with 

 contagious diseases than with others. Second, at high tempera- 

 tures the effect of low humidity is less harmful and of high humid- 

 ity more harmful than with ordinary diseases. This last effect 

 is quite marked. Nevertheless, the optimum is the same no matter 

 which category is considered. 



Such uniformity is most striking, but it is what the biologist 

 would expect. Every species of plant and animal has its optimum 

 temperature, the temperature at which its activities are greatest. 

 It may happen, however, that one kind of activity is greatest at 



