vi HYGIENE OF RESPIRATION 65 



which we work and sleep as well as the clothing we 

 wear should be thoroughly ventilated. 



The subject of ventilation would require no attention 

 if we lived in the open air all the time. But how can 

 we get enough fresh outdoor air to breathe in our school- 

 houses and homes ? This is really not a simple ques- 

 tion to answer, although one of great importance. At 

 each breath we exhale about thirty cubic inches of air 

 or about five hundred cubic inches per minute. We 

 should not rebreathe the air exhaled, for it contains too 

 much injurious matter; but after it has mixed with 

 about one hundred times its volume of fresh air it is 

 again safe to inhale. A person requires then about 

 thirty cubic feet of air per minute. For forty persons 

 in a schoolroom we should take in from the outside at 

 least one thousand two hundred cubic feet of fresh air 

 per minute and allow an equal volume of foul air to 

 escape. 



Careful estimates show that there should be an allow- 

 ance of at least six hundred cubic feet of space for each 

 person in the room. 



The matter of ventilation is one of prime importance 

 and should receive the thoughtful attention of those 

 who construct private and public buildings. School- 

 houses, churches, public halls, and theaters should be 

 provided with ventilating flues as well as with doors and 

 windows. 



Fill a pint fruit jar with water and enter a room. Pour out the 

 water and the air of the room will enter to fill the fruit jar. Now 

 pour two tablespoonfuls of clear limewater into the fruit jar, cover 

 F 



