156 AIR AND LIFE. 



matter in this light, we perceive that birds are the animals that give 

 out the greatest quantity of carbonic acid. While 1 kilogram of ox 

 excretes from 3 to 7 grams of carbon per twenty-four hours, 1 kilogram 

 of fowl or turkey excretes 20 grams on an average, 1 kilogram of young 

 chickens 50 grams, and 1 kilogram of sparrow nearly 00 grams. These 

 facts quite agree with the exceedingly active respiratory function of 

 birds, especially small birds. 



Boussingault many years ago established the fact that the town of 

 Paris alone, taking into consideration men and horses only, exhales 

 nearly half a million cubic meters of carbonic acid per twenty-four 

 hours (at present three-quarters of a million would be nearer the 

 mark, but still even below it), and estimating the whole population of 

 the globe as being one billion and a half, we find that mankind alone 

 pours into the atmosphere one billion and a half kilograms of carbonic 

 acid per diem (1,500,000,000 kilograms) ; that is to say, 720,000,000 cubic 

 meters. Per annum the grand total is, in round numbers, 547,500,- 

 000,000 kilograms, or 202,800,000,000 cubic meters. So much for man- 

 kind only. If we wish to take into account the production of carbonic 

 acid by animals, the difficulties are certainly great, and we can only 

 proceed inferentially, and with less certainty. Girardin puts the j>ro- 

 duction of carbonic acid by animals at something like double that of 

 mankind, if not treble — let us say double, which means 1,095,000,000,000 

 kilograms per annum. But there remain other sources of carbonic acid : 

 all plants which, although decomposing carbon dioxide as part of their 

 method of nutrition, breathe in the same maimer as animals, and exhale 

 carbonic acid ; all the combustions going on in our houses — fires, lights — 

 in our factories and works, etc. (in Europe alone 550,000,000 tons of coal 

 are burned each year, which means 80,000,000,000 cubic meters of carbon 

 dioxide); the slow but uninterrupted production of the gas which is 

 going on over the whole globe tbrough the gradual combustion of 

 decaying vegetable matter; the mineral springs — those of Auvergne 

 only in France, giving off, according to Lecoq, some 7,000,000,000 cubic 

 meters of gas; volcanoes and their surroundings— -Cotopaxi alone being 

 considered by Boussingault as giving off more carbonic acid than a 

 whole city like Paris; the natural sources of gas, such as the Grotta del 

 Cane 1 near Naples, etc. Under such circumstances, it is very difficult 

 to form any idea of the total amount of carbonic acid discharged into 

 the atmosphere. Armancl Gautier, however, comes to the very probable 

 conclusion that this amount can not be very far from 2,500,000,000,000 



■The air in this grotto contains more than half its volume in carbonic acid. It 

 derives its name from the fact that, in order to illustrate the noxious effects of the 

 inferior stratum of air (where carbon dioxide, heavier, accumulates), it is the custom to 

 introduce a dog into it, which soon falls, affected by asphyxia, while the visitors, owing 

 to their higher stature, breathe the normal air, and feel nothing unusual. The dog, 

 it must be added, is at once taken out into pure air, and soon revives, going through 

 the experiment several times a day. Its health is very good, but its temper becomes 

 unpleasant when a visitor appears. The animal knows what is coming. 



