IMPORTANCE OF VARIABILITY 97 



out. In addition to this most patients go back and forth at other 

 times. Moreover, the mere fact of being out of doors means that 

 the patient not only has good air, a fact of the highest impor- 

 tance, but is subjected to far greater changes of temperature 

 than would be the case if the same amount of time were spent in 

 the house. Even the modern practice of "heliotherapy" where 

 the patients are exposed to the sunlight and are gradually 

 toughened until they can be comfortable out of doors with prac- 

 tically no clothing even in winter may owe much of its efficacy to 

 changes of temperature. Certainly the sun falling on the skin 

 causes rapid changes of temperature, for its effect is very different 

 from that which is produced as soon as the patient turns and 

 brings his body into the shade. Moreover, it is noteworthy that 

 the supposed healing effect of sunlight is at a maximum when the 

 skin is tanned to the color of leather and has thus acquired the 

 power to keep out the actinic or chemical rays of the sun which 

 are usually taken to be the effective agent. At such times, how- 

 ever, the patient has become so hardened to the air that he can 

 and does endure the most extreme and rapid changes of tem- 

 perature without discomfort. Perhaps these changes are as 

 effective as the sunlight. 



Apparently one of the best possible safeguards of health is 

 constant changes of temperature. We need to return to the 

 conditions under which the evolution of our unclothed ancestors 

 took place. In places where healthy people work, as well as in hos- 

 pitals, the ideal practice would seem to be to keep the temperature 

 constantly varying. The extent of the variations must of course 

 depend upon the circumstances, but even patients who are very 

 sick can usually stand a sudden, sharp drop provided the return 

 to warm conditions is speedy enough. If we have rightly inter- 

 preted the New York figures such variability will strengthen most 

 patients throughout their illness. Then when the actual crisis 

 of the disease arrives it would seem as if the patient should be 

 subjected to a sudden drop of temperature at just the time when 



