858 SPECIAL PHYSIOLOGY. 



depressing effects upon, and ultimate injurious consequences to, the 

 system. 



During each minute, an ordinary adult inspires and expires 360 

 cubic inches of air, exhales 14.4 cubic inches of carbonic acid, and 

 absorbs at least 15 cubic inches of oxygen ; this renders 150 cubic 

 inches of air totally irrespirable ; for, as already mentioned, this con- 

 dition is arrived at, when half the normal quantity of oxygen (30 parts 

 in 150) is replaced by carbonic acid. But in order that the air of 

 any room should be fit for continuous respiration, a much greater 

 change must be effected in it, than that of merely replacing, minute 

 by minute, the 360 cubic inches of air breathed in that time. For 

 the 4 per cent, of carbonic acid contained in it, is sufficient, with the 

 concurrent loss of oxygen, to deteriorate a much larger quantity of 

 air. It is 100 times more than that which is present in common air, 

 for this is only .04 per cent. ; and therefore, even when diluted with 

 100 times its volume of ordinary air, the mixture would still contain 

 twice the normal quantity of carbonic acid, viz., .08 per cent., or 8 

 parts in 10,000; this is about the average quantity in the air of cer- 

 tain large manufacturing towns. For such a dilution, 36,000 cubic 

 inches, or more than 20 cubic feet of air would be required. Owing, 

 however, to the rapid, spontaneous, dry diffusion of the carbonic acid, 

 a less degree of actual dilution is sufficient for the purposes of healthy 

 respiration; and it has been variously computed, that from 4 to 10 

 cubic feet of air per minute, which last-named quantity, with the re- 

 spired air, would yield an atmosphere containing 12 parts of carbonic 

 acid in 10,000, are needed for each person, in sleeping or sitting 

 apartments, schools, courts, theatres, workshops, factories, barracks, 

 workhouses, or prisons. Hospitals, especially for surgical cases or 

 fevers, require at least double that quantity. Much depends on the 

 temperature of the air, for a higher temperature requires a more rapid 

 change. Moreover, besides the removal of carbonic acid and the re- 

 newal of oxygen, it is of the utmost moment that other pulmonary and 

 cutaneous exhalations, which contain volatile organic matter and am- 

 moniacal salts, should be diluted, oxidated, or removed. If the prod- 

 ucts of the combustion of artificial lights, especially of gas, enter the 

 air of the room, a still further allowance of fresh air is necessary. 



Were it not for the law of diffusion of gases, the evils arising from 

 overcrowded and ill-ventilated rooms would be much greater. In the 

 air of a very close room, which had been occupied by 500 people, and 

 in which fifty candles had been burning, Dr. Dalton found, after it 

 had been shut up for two hours, one per cent, of carbonic acid. But 

 Dr. Roscoe has shown that in theatres, the percentage is usually .0321, 

 and in schoolrooms .331; indeed, in no rooms did he ever find more 

 than .5 per cent., owing, as he remarks, to the constant diffusion and 

 interchange of air through the crevices and openings at the doors, 

 windows, and fire-place. Furthermore, in proof of the rapidity and 

 importance of the diffusion of carbonic acid in the air, he found that 

 the percentage of carbonic acid was nearly uniform in every part of 

 an occupied room, at the same time. Nevertheless, this accidental 

 diffusion is insufficient for the proper change of the air in a crowded 



