IMPOETANCE 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. 

 ISTow 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 1-1 00th 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- 

 portionably greater, if there be an additional consumption of 



