RESPIRATION AND EXCRETION 



335 





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formed. The carbon dioxide in the blood stimulates the nervous center 

 which has control of respiration to greater activity, and quickened inspira- 

 tion follows. 



Need of Ventilation. - - During the course of a day the lungs 

 lose to the surrounding air nearly two pounds of carbon diox- 

 ide. This means that about three fifths of a cubic foot is given 

 off by each person during an hour. When we are confined for 

 some time in a room, it becomes necessary to get rid of this 

 carbon dioxide. This can be done only by means of proper 

 ventilation. A considerable amount of moisture is given off from 

 the body, and this moisture in a crowded room is responsible for 

 much of the discomfort. The air becomes humid and uncomfort- 

 able. It has been found that by keeping the air in motion in such 

 a room (as through the use of electric o \ _ -^-----srr-, | / 

 fans) much of this discomfort is 

 obviated. 



The presence of impurities in the 

 air of a room may easily be deter- 

 mined by its odor. The odor of a 

 poorly ventilated room is due to 

 organic impurities given off with the 

 carbon dioxide. This, fortunately, - 

 gives us an index of the amount of 

 waste material in the air. Among 

 the factors which take oxygen from 

 the air in a closed room and produce 

 carbon dioxide are burning gas or oil 

 lamps and stoves, and the presence 

 of a number of people. 



Proper Ventilation. - Ventilation 

 consists in the removal of air that 

 has been used, and the introduction 

 of a fresh supply to take its place. 



Heated air rises, Carrying with it Three ways of ventilating a room, 

 i c ji i ] i i i, inlet for air ; o, outlet for air. 



much of the carbon dioxide and ^ hich is the ' b ; st method of 

 other impurities. A good method ventilation? Explain. 





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