226 STUDIES IN PHYSIOLOGY 



other until they come to lie above the head. In this 

 way air is drawn in through the nose and mouth. When 

 the elbows are carried downward and pressed upon the chest> 

 the air is forced out of the body. These two movements 

 should be alternated regularly every few seconds, and hope 

 of resuscitation by this and other means should not be aban- 

 doned until several hours have elapsed. 



Necessity of Ventilation. Every act of respiration removes 

 about five parts of oxygen from every one hundred parts of 

 the air taken into the body, and adds to each one hundred 

 parts over four parts of carbon dioxid, together with the 

 poisonous organic compounds mentioned on page 221. One 

 might breathe in this air a second time and still be able to 

 extract oxygen from it. The presence of chemically pure 

 carbon dioxid in air even in considerable quantity is not 

 necessarily dangerous ; but to take into the body again the 

 organic wastes that have once been given off, is most 

 unhealthful. The first effect of foul air is a feeling of 

 sleepiness and headache, and if larger quantities are in- 

 spired, the body becomes poisoned. We see, then, the abso- 

 lute necessity of having the air in a living room changed 

 frequently. The air that has been once used must be removed 

 and a fresh supply must be furnished; this is what is meant 

 by ven-ti-la'tion. 



Methods of Ventilation. It is important to remember that 

 fresh air is not necessarily cold air, and that draughts of 

 air are not required, indeed that they are undesirable. The 

 problem of ventilation is that of furnishing a sufficient 

 quantity of wholesome air of the proper temperature, and 

 of removing the foul air. It is evident that this is rather 

 difficult to accomplish in schoolrooms or in public halls. 

 Air will not of itself circulate rapidly enough, and so it has 

 to be forced into these rooms by large blowers or revolving 

 fans in the basement. Hot-air pipes or fans are likewise 

 often employed at the top of the ventilating flues to draw 

 out the foul air. Since warm air is lighter than cool air, the 



