184 RESPIRATION 



Through experimentation, scientists have discovered that people 

 are most uncomfortable in still air. Under the clothing, in close 

 contact with the skin, is a blanket of air. This air absorbs per- 

 spiration, body odors, and the excess body heat. If this air can- 

 not circulate, it becomes moist, and the perspiration does not 

 evaporate as it should. If air in a room is set in motion by an 

 electric fan, the contaminated and moist air moves, and cooler 

 and drier air takes its place. This brings relief to the body. For 

 years, people thought ventilation consisted largely of getting rid 



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The exchange of carbon dioxide and oxygen between the air sacs and blood vessels is external 

 respiration ; between the cells and blood vessels it is known as internal respiration. 



of carbon dioxide. Now it is known that ventilation problems 

 also involve the control of body odors, heat, and moisture. 



When air is set in motion, the stagnant air is removed and 

 fresh air is brought in contact with the body. Air that is best 

 for breathing should be at a temperature from about 65 degrees 

 to 70 degrees. It must be slightly moist, must be moving, and 

 must be free from dust and impurities. The problem of venti- 

 lation is to treat the atmosphere of a room so that air will have 

 at all times the four characteristics mentioned. 



