CLIMATE AND HEALTH 75 



one temperature and another at another. Little one-celled 

 creatures called paramoecia and amoebas, cold-blooded crustaceans 

 such as the crayfish, amphibians like the frog, and warm-blooded 

 animals like mice, not to mention a host of plants, have all been 

 tested in this respect. In each the best temperature for a given 

 activity seems to be constant for the species. It seems highly 

 probable that when fuller data are available we shall find that 

 even the negro has the same optimum as the rest of the human 

 race. Perhaps the temperature optimum is something like the 

 temperature of the blood which is the same for all races, and does 

 not vary from the tropics to the poles. Indeed, it seems quite 

 probable that man's uniform response to the outside temperature 

 is due to the fact that his inside temperature remains always 

 the same. 



If men of all races are physically at their best at a mean tem- 

 perature of 64°, why are not the people of the Hawaiian Islands, 

 for example, who have lived for many generations in almost that 

 temperature, the strongest in the world? Why are they not able 

 to endure as the white man endures? Why have they not 

 developed a high civilization? The answer is twofold. First, the 

 optimum for mental activity is not the same as for physical, and 

 second, temperature is by no means the only factor. As to mental 

 activity the matter has not yet been investigated so fully as could 

 be wished. Nevertheless the investigations of Lehmann and 

 Pedersen on school children, the general results of observations 

 on mental activity in many countries, and my own study of the 

 marks of over 1,600 students at West Point and Annapolis indi- 

 cate that the best mental work is done at a temperature decidedly 

 lower than the physical optimum. At both West Point and 

 Annapolis the students do the best work when the temperature 

 averages about 40°. As I have explained in "Civilization and 

 Climate," this happens in spite of the fact that the season when 

 this temperature prevails is different in the two places. Whether 

 the true mental optimum is 40°, that is, when there are mild frosts 



