IMPORTANCE OF FREE VENTILATION. 285 
animal life ; for it prevents the due excretion by the lungs of 
that which has been formed within the body ; and the latter 
consequently accumulates in the blood, and exercises a very 
depressing influence on the action of the various organs of the 
body, but particularly on that of the nervous system. The 
usual proportion is not above 1 part in 5000 ; and when this 
is increased to 1 part in 100, its injurious effects begin to be 
felt by Man, in headache, languor, and general oppression. 
Now it is evident, from the statements in the last paragraph, 
that, as a man produces in twenty-four hours about 15 cubic 
feet of carbonic acid, if he were inclosed in a space containing 
1500 cubic feet of air (such as would exist in a room 15 feet 
by 10, and 10 feet high), he would in twenty-four hours 
communicate to its atmosphere from his lungs as much as 
1 part in 100 of carbonic acid, provided that no interchange 
takes place between the air within and the air outside the 
chamber. The amount would be further increased by the car- 
bonic acid thrown off by the skin, the quantity of which has 
not yet been determined. 
336. In practice, such an occurrence is seldom likely to 
take place ; since in no chamber that is ever constructed, 
except for the sake of experiment, are the fittings so close as 
to prevent a certain interchange of the contained air with 
that on the outside. But the same injurious effect is often 
produced by the collection of a large number of persons for a 
shorter time, in a room insufficiently provided with the means 
of ventilation. It is evident that if twelve persons were to 
occupy such a chamber for two hours, they would produce the 
same effect with that occasioned by one person in twenty-four 
hours. Now we will suppose 1200 persons to remain in a 
church or assembly-room for two hours; they will jointly 
produce 1500 cubic feet of carbonic acid in that time. Let 
the dimensions of such a building be taken at 100 feet long, 
50 broad, and 30 high; then its cubical content will be 
(100 x 50 x 30) 150,000 cubic feet. And thus an amount 
_ of carbonic acid, equal to 1-100th part of the whole, will be 
_ communicated to the air of such a building, in the short space 
_ of two hours, by the presence of 1200 people, if no pro- 
Vision be made for ventilating it. And the quantity will 
_ be greatly increased, and. the injurious effects will be pro- 
Pportionably greater, if there be an additional consumption of 
