900 EDWAKD C. 



influence of each of these atmospheric factors will be briefly considered. 

 Pressure will be discussed under altitude. 



Temperature and Humidity 



Although man is a homothermal organism, there is a certain relation- 

 ship between his body temperature and the temperature of his environ- 

 ment. His internal temperature, in health, remains fairly constant wher- 

 ever he may be, varying not more than 1 or 2 F. Man readily adapts 

 himself to extremes of temperature through responses made by his vaso- 

 motor system and sweat glands. He is constantly and of necessity elimi- 

 nating heat. The loss of heat results from radiation, conduction and evapo- 

 ration. The amount of heat lost by radiation and conduction depends 

 largely upon the temperature of the surrounding air, while the amount 

 lost from evaporation depends upon the relative humidity of his immediate 

 environment. Some conditions permit loss of heat by radiation and con- 

 duction only. In a dry hot climate loss of heat by evaporation is at its 

 maximum. The New York State Commission on Ventilation found that 

 during the months of June and July the rectal temperature of man at 8 

 A. M. was conditioned by the average atmospheric temperature of the 

 preceding night and that a difference of about 1 F. resulted from a 

 difference of 36 F. in atmospheric temperature. The temperature of a 

 chamber influenced the body temperature of healthy human beings, con- 

 fined for periods ranging from 4 to 7 hours, the body temperature falling 

 in an atmosphere of 68 F. and fifty per cent relative humidity; rising 

 in one of 8G F. and 80 per cent relative humidity; and remaining 

 nearly stationary in air of 75 F. and 50 per cent relative humidity. A 

 stay of three and one quarter hours in an atmosphere of 104.7 F. and 95 

 per cent relative humidity caused the body temperature to rise 6 F. (25). 



Shaklee, working with the native monkey in the Philippine Islands, 

 found that exposure to the sun by placing the animal on the ground or a 

 roof caused death within six hours from a rise in body temperature. It 

 was possible to gradually acclimatize the animals, this being accomplished 

 by an increased capacity for sweating, which kept the body heat well 

 within the killing temperature, although it rose several degrees. 



In hot climates radiation and conduction become less important and 

 evaporation the most important factor in eliminating heat. Evaporation 

 in its turn depends upon the relative humidity of the air and, to some 

 extent, upon the presence of winds. 



The circulatory system is also affected by the temperature and hu- 

 midity of the atmosphere, the rate of heart beat being increased con- 

 comitantly with the body temperature; it is increased in warm humid 

 air and decreased in cool, dry air. Eastman and Lee found that the pulse 



