RESPIRATION AND EXCRETION 



335 



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 



O I-,'.'. V_l?!rl---Iv} : 1 :t ' - ^ J i 



■- -it~' -' 



— _. -^ ^ 



a 



o 



a room (as through the use of electric 

 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. 



much of the carbon dioxide and WS tttV brrt'^dt, 



other impurities. A good method ventilation? Explain. 





] 



o 





.'. '*- ------i^---- 



1 



