CHAPTER XVI 



HYGIENE OF RESPIRATION AND VENTILATION 



Questions. 1. Why is outdoor air better than indoor air ? 2. Why 

 does dry air feel colder than moist air ? 3. What is the harm in breathing 

 through the mouth ? 4. Is it bad to run until you are out of breath ? 

 5. Why are drafts dangerous ? 



139. Ventilation and its problems. Every breath we take re- 

 moves from the air a certain amount of oxygen and replaces it 

 with carbon dioxid. In order to keep up the working power the 

 body must be supplied with enough air to furnish the needed 

 oxygen and to carry away the excreted carbon dioxid. Of 

 course it is not necessary to change all the air in a room for 

 every breath. It is safe to use air in which the amount of 

 carbon dioxid has been increased from about three or four parts 

 in 10.000 (what it is in ordinary outdoor air) to 6 parts in 

 10,000, or even much more (see Fig. 88). How much fresh air 

 should be supplied for each person in a school or factory ? Re- 

 cent experiments show that under ordinary conditions the air 

 contains neither a "breath poison" nor a dangerous amount of 

 carbon dioxid, even when the ventilation is decidedly bad. Nor 

 is there danger that the proportion of oxygen will fall below a 

 safe limit. The chief problems of ventilation are (i) to keep 

 the air at a suitable temperature, (2) to regulate the moisture 

 and dust in the air, and (3) to keep the air in motion. 



I. Temperature. The temperature of the air in a living 

 room, schoolroom, or workshop should be kept as nearly as 

 possible at 65° F. At this temperature the internal temperature 

 of the body or blood remains fairly constant (at about 98^° F.) 

 through the steady radiation of heat from the surface and 

 through the evaporation of water. As the temperature rises we 

 remain comfortable by increasing sweat or perspiration and 



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