AIR AND LIFE. 157 



cubic meters per anuuin, which means over 5,000,000,000,000 kilograms, 

 the weight of the total atmosphere being 5,000,000,000,000,000,000— that 

 is, one hundred thousand times greater. At all events, this is certainly 

 below the mark. 



Such beiug the enormous rate of production of carbonic acid, one 

 may well wonder that the ratio of this gas in the total atmosphere 

 remains as small as it is, it being easy enough to reckon what the ratio 

 would become in the course of ten, twenty, or a hundred years, if there 

 were not some agency at work by means of which it is destroyed or com- 

 bined, and without which life would soon become extinct. That such 

 agencies do exist and are in operation is a positive fact, and though we 

 may not be acquainted with all of them, there are three at least which 

 deserve notice. These agencies are plants, animals, and oceans. 



Plants occupy the first place; for, while producing carbonic acid which 

 they breathe, they absorb it in the course of the process of nutrition, 

 taking its carbon into their tissues and yielding its oxygen to the 

 atmosphere. 1 



Animals should be considered next; not all, to be sure, but all those 

 which have a calcareous skeleton, internal or external. Such are corals, 

 such are shellfish generally, and all aquatic and terrestrial animals, 

 which, having a calcareous skeleton, must necessarily contain some 

 amount of carbonic acid combined with lime. This compound seems 

 to hold good for a long time, and if there are cases where the skeleton 

 after death slowly decomposes, so that the carbonic acid has some 

 chances of getting free again, there are a great many more in which it 

 is preserved, and we know of considerable geological strata which are 

 nothing else than enormous accumulations of the remains of animals that 

 died centuries and hundreds of centuries ago. This process, by means 

 of which a considerable amount of carbonic acid becomes fixed and 

 imprisoned, so to say, was exceedingly active in earlier times; it is also 

 very active at the present period, and the great space taken up by coral 

 reefs in the mid Pacific and other oceans is but a gigantic laboratory of 

 nature where carbonic acid is being, if not destroyed, at least hoarded 

 and put by under a compact form, and, for a time at least, withdrawn 

 from the general circulation of matter. To appreciate the importance 

 of the storing process, it is only necessary to measure the thickness 



] A writer in the Belgique Horticole, Vol. XXXV, 1885, p. 227, gives the following 

 evaluation: One hectare of forest (1 hectare equals 2.471 acres) produces yearly 

 3,000 kilograms of carbon— 1,600 kilograms under the form of wood and 1,400 under 

 the form of leaves (weighed dry and exclusive of other substances). During one 

 hundred and fifty days (on the average) of active vegetation, the trees must draw 

 from the atmosphere 5,596 cubic meters (11,000 kilograms) of carbon dioxide. In 

 exchange they give nearly as much oxygen (5,594 cubic meters). With a field of 

 oats the same proportion obtains — as much oxygen is given off as carbonic acid 

 is taken in. Thirty-two persons give off as much carbonic acid as is taken in by 1 

 hectare of oats or of forest, and they burn as much oxygen as the said surface of 

 field or forest produces. 



