Since at each breath some oxygen is taken from the air and some carbon dioxide given to it, were the atmosphere around a living person 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 determined by the number of persons collected in a room: the supply which would be ample for one person would be insufficient 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 used.

What 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 inspired, 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?