296 THE INVISIBLE WORLD 



But one may take into his system the tiniest 

 speck of any kind of poison with no harm some- 

 times perhaps with good. 



Hence Nature allows her atmosphere to contain 

 everywhere the tiny speck of carbonic acid. Of air 

 in its normal condition -fa of one per cent, is car- 

 bonic acid. This tiny amount of poison does no 

 harm ; it may do good. 



But this is Nature's limit. To increase the per 

 cent, of acid is danger. One per cent, is decidedly 

 against health. Ten per cent, is fatal, it kills. 



Look at Fig. 110. The paper box contains thirty 

 cubic feet of air. It fits closely around the neck, 

 and is air tight. From without no air can come 

 in; from within none can go out. 



The first breath of the man takes from the box 

 twenty cubic inches of good air, and throws back 

 into the box the same amount of carbonic acid and 

 watery vapor. All the air in the box is thus 

 tainted. Every succeeding breath taints it more 

 and more, until the man has nothing to breathe but 

 poison. In twenty minutes he is dead suffo- 

 cated and poisoned by bad air. 



An English fort in Calcutta was garrisoned by 

 146 English soldiers. The Indian captain captured 

 the fort, and chucked the soldiers into a dungeon 

 for the night. The dungeon was 18 feet square, 

 with two small windows. At the end of eight hours 

 the captain, returning to the fort, found 123 of the 

 soldiers dead, and the others no better than dead 

 suffocated and poisoned by bad air. 



