AIR AND LIFE. 175 



they seem to be surrounded by a host of very brilliant lights, while 

 exquisite music is played by some invisible orchestra. But this state 

 is of short duration, and total unconsciousness soon occurs, which, if 

 the toxic gas keeps on accumulating in the blood, is rapidly converted 

 into eternal sleep. Cases of death by carbonic acid are not infrequent; 

 they are met with particularly in the vicinity of fermenting liquids, 

 such as brewers' vats or wine cellars; in places where carbon dioxide is 

 naturally exhaled by "gas springs;" by thermal springs in some caves 

 or grottoes, and in all ill-ventilated rooms where a proportionately large 

 number of men or animals are gathered. In lecture and assembly 

 rooms, which are often crowded, air vitiates rapidly; in theaters, in 

 schools, in lecture halls, as much as 10 parts per thousand of carbonic 

 acid has been observed, and in Alpine stables, as before referred to, 

 where animals and men were crowded together, each seeking some 

 warmth in the close viciuity of his neighbor, the ratio of 21 parts per 

 thousand has been recorded. 1 Such atmosphere is toxic," and proofs 

 thereof are not wanting. 



l M. G. H. Richards, of the Massachusetts Institute of Technology, has, during 

 nine years past, made some 5,000 analyses of the air of lecture rooms. The nor- 

 mal average proportion of carbonic acid in external air is between 3.7 and 4.2 per 

 10,000. In buildings, the proportion increases according to circumstances. For 

 instance, in empty rooms it is higher by 0.5 on the average in consequence of the 

 decomposition of organic. matter, which always remains after the passage of any 

 number of human beings, in the cracks of the floor, on the walls, etc. In the parts 

 of the building where people come and go, without stopping for any considerable 

 time, the ratio is a little higher, and becomes 5 per 10,000. In lecture rooms things 

 are at the worst, as might be expected, and the ratio is 6 or 8 and occasionally 10 

 or 12 volumes of carbonic acid per 10,000 of air. If such proportions are exceeded, 

 work becomes difficult and unprofitable. Each adult exhales, on an average, accord- 

 ing to Andral and Gavarret, some 22 liters of carbon dioxide per hour, so that a 

 man breathing in a confined space 3 meters long, 2 meters high, and 2 meters wide 

 would in twenty-four hours transform the whole of the air of this space into an 

 air having exactly the composition of that exhaled from the lungs. It must not 

 be forgotten that each gaslight, on an average, produces 128 liters of carbon dioxide 

 per hour, and 10 grams of candle produce 14 liters. Under such circumstances no 

 one can wonder that the atmosphere becomes so soon vitiated in rooms where any 

 considerable number of persons are assembled. 



-It is toxic in its natural condition, by which is meant, if oxygen is present in it 

 only in the usual proportion. But, experimentally, such atmosphere may be pre- 

 vented from becoming dangerous if its composition is altered by an addition of 

 oxygen. Regnault and Reiset have seen dogs and rabbits live in an atmosphere con- 

 taining 25 per cent carbon dioxide, 30 to 40 per cent oxygen, and about 40 per cent 

 nitrogen. Even without increasing the ratio of oxygen, animals may live a short 

 time in an atmosphere containing a large proportion of carbon dioxide — 30 per cent, 

 for instance, oxygen being 16 per cent (Le Blanc) ; and Snow has seen birds withstand 

 some time the effects of an atmosphere containing 21 per cent oxygen, 59 nitrogen 

 and 20 carbonic acid. But these experiments can not have any considerable dura- 

 tion, and the average limit of respirable atmosphere is set by the composition of 

 expired air. An atmosphere containing 4 per cent carbon dioxide, 16 per cent 

 oxygen, and 80 per cent nitrogen is inadequate to long maintain life. A lamp is 

 soon extinguished in such an atmosphere, but man may live in it for a short time. 



To avoid any danger of the vitiation of air, hygienists are agreed that more is 



