THE AIR AND LIFE. 525 



All living' beings are piodiicers of carbonic acid, and all breathe, 

 although with varied force. Respiration, chemically considered, is the 

 combination of a certain quantity of carbon of the body and a certain 

 quantity of oxygen of the air; it is a manufacture of carbonic acid 

 which is expelled by the lungs. This constant evolution of carbonic 

 dcid by animals and also by plants, which breathe like animals, cer- 

 tainly varies in intensity; and we know that in the same species of 

 animal, for example, the male produces more than the female, the adult 

 more than the very young or the very old, the strong more than the 

 weak, etc. Everyone knows also that this production is increased by 

 exercise, by movement, by sunlight, by the taking of food; diminished 

 by rest, by darkness, by want of food. It nmy be said that on the aver- 

 age man exhales 20 liters of carbonic acid every hour, or nearly a kilo- 

 gram in the twenty-four. The sheep produces more and the bull about 

 7 and 8 kilograms. To fully appreciate, however, the rate of produc- 

 tion of carbonic acid by animals, let us state it differentl}^ and bring it 

 down to a common unit, the kilogram of the weight of an animal. 

 The total amount produced will then be compared with the number of 

 kilograms that the animal weighs, and we can say that a kilogram of 

 horse or ox, or of duck, pi'oduces such and such a quantity every 

 twenty-four hours, liy this method we find that birds are the greatest 

 producers of carbonic acid. A kilogram of ox excretes from 3 to 7 

 grams of carbon every twenty-four hours, a kilogram of turkey about 

 20 grams, a kilogram of newly-hatched chicks 56 grams, and of spar- 

 rows nearly 00 grams. This ought not to surprise us, for we know that 

 the respiratory activity of birds is very great, and the consequent pro- 

 duction of carbonic acid necessarily large. 



Boussingault made the calculation, some time ago, that the city of 

 Paris alone produces from men and horses about a half a million cubic 

 meters every twenty-four hours. At the present time these figures 

 would be much larger, and if we estimate the total population of the 

 globe at a thousand million, the ('ondusion is evident that man alone 

 casts oii" 480,000,000 of cubic meters of carbonic acid per day into the 

 atmosphere; in other words, 175,200,000,000 of cubic meters per year ! 

 It is difficult to calculate the exact production for animals, but it is cer- 

 tainly do.uble or triple, according to (lirardin. We may call the amount 

 produced by animals aud men together 700,000,000,000 of cubic meters 

 per year. If we .add to this the productions from plants, from the com- 

 bustion of wood and coal, the slow i)roductiou from the whole terres- 

 tiial surface where vegetable matter is decaying, from mineral sources, 

 from volcanoes and their surroundings (Cotopaxi exhales, according to 

 Boussingault, more than all Paris), from natural springs, from terres- 

 trial depths, it will not surprise us that Mr. Armand Gautier concludes 

 that 2,500,000,000,000 \2h billion] of cubic meters of carbonic acid is 

 produced every year. And even that enormous sum is certainly less 

 than the actual fact. 



