THE EFFECT OF CLIMATE AND WEATHER 317 



as when the temperature varies above and below the 

 optimum. In other words the most favorable condition is a 

 variable temperature whose average is the optimum. Similar 

 experiments have not yet been performed upon human 

 beings to any appreciable degree, but studies of factory 

 work and death rates indicate that man is benefitted by 

 variabihty quite as much as are plants. 



The daily deaths in New York City illustrate the matter. 

 At all seasons, summer and winter alike, a drop of tem- 

 perature is systematically accompanied by a drop in the 

 death rate. It is reasonable enough that in summer a drop 

 from a high temperature toward the optimum should reduce 

 the death rate, but how can a drop downward away from the 

 optimum in winter produce the same result? Although the 

 exact physiological processes are not yet known, the answer 

 appears to be that the conditions are analogous to those of a 

 cold bath. A healthy adult can take a dip in cold water and 

 emerge with a decided glow of warmth and with a stimulus 

 to activity and health which lasts for hours. But let that 

 same person stay in water with a temperature of 50° for 

 an hour or two, and he may be so chilled that he will not 

 recover for days. 



The analogy of the hot bath perhaps applies to the 

 seemingly unreasonable proposition that even in winter a 

 rise of temperature is accompanied by an immediate rise 

 in the death rate, but the case is not clear. If bath water 

 of almost any temperature is gradually warmed, a feeling of 

 relaxation generally ensues, which perhaps means less 

 power to resist disease. A less speculative cause of a rising 

 death rate associated with a rise of temperature even when 

 the temperature thereby approaches the optimum is found 

 in the almost universal tendency for houses to be greatly 

 heated on days when the outside temperature is rising or 

 has just finished rising. We cannot seem to make our fur- 

 naces and our windows keep pace with the weather. If we 

 were able to do this, much of the rise in the death rate 

 because of a rise in the winter temperature might possibly 

 be eliminated. Each month in the year the same conditions 

 are manifest: many deaths when the temperature rises, 

 few when it falls. 



