VENTILATION. 375 



being 4.3 per cent of the volume of the air breathed 

 daily, is 10,800 X 4.3 + 100 = 464.4 liters (16.25 cubic 

 feet) measured at the normal temperature and pressure. 

 This volume weighs 910 grams, or 14,1)5 grains. 



If the expired 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 consequence 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 per cent of oxygen and 

 gained only 4. 3 of carbon dioxide. In round numbers, 100 

 volumes of dry inspired air at zero, give 99 volumes of dry 

 expired air measured at the same temperature and pres- 

 sure. 



Ventilation. Since at every 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 ven- 

 tilation 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- 

 sufficient for two. Moreover fires, gas, and lamps, all use 

 up the oxygen of the air and give carbon dioxide to it, and 

 hence calculation must be made for them in arranging for 

 the ventilation of a building in which they are to be em- 

 ployed. 



In order that air be unwholesome to breathe, it is by 

 no means necessary that it have lost so much of its oxygen 

 as to make it difficult for the Body to get what it wants of 

 that gas. The evil results of insufficient air-supply are 

 rarely, if ever, due to that cause even in the worst ventilated 

 room for, as we shall see hereafter (p. 384), the blood can 

 take what oxygen it wants from air containing compara- 



