RESPIRATION. 139 



same time, and spoils about as much air as ten men. A 

 fire burning in a grate or stove emits some gaseous impur- 

 ity, and at the same time abstracts from the air as much 

 oxygen as twelve men would consume in the same period, 

 thus increasing the relative amount of carbonic acid in 

 the air. From furnaces, as ordinarily constructed, this gas, 

 with other products of combustion, is constantly leaking 

 and vitiating the air of tightly-closed apartments. 



34. Effects of Impure Air. Carbonic acid, in its 

 pure form, is irrespirable, causing rapid death by suffoca- 

 tion. Air containing forty parts per thousand of this gas 

 (the composition of the expired breath) extinguishes a 

 lighted candle, and is fatal to birds ; when containing one 

 hundred parts, it no longer yields oxygen to man and 

 other warm-blooded animals; and is of course at once 

 fatal to them. In smaller quantities, this gas causes head- 

 ache, labored respiration, palpitation, unconsciousness, and 

 convulsions. , 



35. In crowded and badly ventilated apartments, where 

 the atmosphere relatively contains from six to ten times 

 the natural amount of carbonic acid, the contaminated air 

 causes dulness, drowsiness, and faintness; the dark, im- 

 pure blood circulating through the brain, oppressing that 

 organ and causing it to act like a blunted tool. This is a 

 condition not uncommon in our schools, churches, court- 

 rooms, and the like, the places of all others where it is 

 desirable that the mind should be alert and free to act; 

 but, unhappily, an unseen physiological cause is at work, 

 dispensing weariness and stupor over juries, audience, and 

 pupils. 



36. Another unmistakable result of living in and breath- 

 ing foul air is found in certain diseases of the lungs, 

 especially consumption. For many years the barracks of 



34. Effects of inhaling carbonic acid alone ? In email quantities? 



35. Effects of the air in crowded and badly ventilated rooms? 



36. A cause of consumption ? How was the fact illustrated ? 



