VENTILATION. 253 



very little thing, on calculation it is obvious that the total 

 amount of matter received into the body from the lungs, 

 and that passed out of it by these organs, every day of our 

 lives is considerable. In a year each adult breathes about 

 10,000 Ibs. of air ; from it he takes 657 Ibs. of oxygen, and 

 to it he gives off 730 Ibs. of carbon dioxide. 



Changes of Volume in Air once breathed. If the ex- 

 pired air be measured as it leaves the body its bulk will be 

 found greater than that of the inspired air, since it not 

 only has water vapor added to it, but is expanded in con- 

 sequence of its higher temperature. If, however, it be dried 

 and reduced to the same temperature as the inspired air, 

 its volume will be found diminished, since it has lost 5.4 

 volumes of oxygen for every 4.3 volumes of carbon dioxide 

 which it has gained. 



Ventilation. Since at each breath some oxygen is taken 

 from the air and some carbon dioxide given to it, were 

 the atmosphere around a living man not renewed he would 

 at last be unable to get from the air the oxygen he required; 

 he would die of oxygen starvation or be suffocated, as such 

 a mode of death is called, as surely, though not quite so 

 fast, as if he were put under the receiver of an air-pump 

 and all the air around him removed. Hence the necessity 

 of ventilation to supply fresh air in place of that breathed, 

 and clearly the amount of fresh air requisite must be deter- 

 mined by the number of persons collected in a room: the 

 supply which would be ample for one person would be in- 



Wliat weight of air is breathed yearly by an adult? How much 

 oxygen is taken from it? How much carbon dioxide is given to it? 



How does the air expired differ in bulk from inspired? Why? 

 If the expired air be dried and cooled to the temperature of the in- 

 spired, what is found? Why? 



Why would a man die if the air around him were not renewed? 

 What is suffocation? What is the object of ventilation? 



