Every one should become intelligent in relation to the matter of ventilation, and should appreciate its importance.

Vast and irreparable injury frequently results from the confinement of several scores or hundreds of people in a schoolroom, church, or lecture room, without adequate means of removing the impurities thrown off from their lungs and bodies.

The same air being breathed over and over becomes densely charged with poisons, which render the blood impure, lessen the bodily resistance, and induce susceptibility to taking cold, and to infection with the germs of pneumonia, consumption, and other infectious diseases, which are always present in a very crowded audience room.

Suppose, for example, a thousand persons are seated in a room forty feet in width, sixty in length, and fifteen in height: how long a time would elapse before the air of such a room would become unfit for further respiration?
Remembering that each person spoils one foot of air every second, it is clear that one thousand cubic feet of air will be contaminated for every second that the room is occupied.

To ascertain the number of seconds which would elapse before the entire air contained in the room will be contaminated, so that it is unfit for further breathing, we have only to divide the cubic contents of the room by one thousand.