236 APPLIED PHYSIOLOGY 



like the boiling of water in a teakettle, where the heat passes off in the 

 steam, so that the temperature of the water does not rise beyond the 

 boiling point. Some perspiration is given off even if the body is cold, 

 but with an overproduction of heat more perspiration is often pro- 

 duced than can be turned into vapor. A person is usually said to per- 

 spire only when it is produced in so great a quantity that it collects in 

 drops upon the skin. 



414. Moisture in the air. When there is a great amount of 

 moisture in the air on a hot summer's day, the perspiration does not 

 evaporate from the skin, and so heat is retained within the body, and 

 the air seems " heavy " and oppressive. On such days the humidity of 

 the air is said to be great. Dry air at a temperature of 90 or 95 degrees 

 seems cooler than moist, humid air at a temperature of 80. 



415. Sunstroke. Men and animals, while working, pro- 

 duce a large amount of heat. On excessively hot and humid 

 days the extra heat may not pass off so fast as it is formed, 

 but may accumulate until the temperature rises several 

 degrees. The increased heat overwhelms the body, and 

 produces a sudden attack of faintness called sunstroke. 

 The unconsciousness lasts for a long time, and is followed 

 by great weakness, and sometimes by death. When a 

 person is sunstruck he should be laid in a cool place, with 

 his head lowest. Cold water should be dashed upon his 

 head and chest. His limbs should be rubbed to help the 

 circulation. 



416. Damp days in winter. While moisture in the air makes 

 the body warmer in summer, in the winter it makes the air seem colder. 

 Dry air is a poor conductor of heat, but a little moisture makes it a 

 much better conductor. So a damp wind rapidly extracts the heat 

 from the body, and seems to penetrate even thick clothing. Moist air 

 at a temperature of 20 degrees seems colder than dry air at zero. 



417. Heating living rooms. In addition to the means 

 provided by nature, man is often compelled to add devices 

 of his own for regulating the heat of his body. Man lives 



