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But before we determine, upon these statements, quite to 

 disregard this action of plants as unimportant and unworthy 

 of notice, we must consider, in the first place, that the oppo- 

 site effects of animal and of vegetable life are quite certain, 

 and that the only question is one of time ; viz., in what time 

 would the action of either prove injurious if uncounteracted 

 by the other. And likewise we must notice the great 

 uncertainty and liability to error to which these calcula- 

 tions of MM. Dumas and Boussingault are liable. They 

 estimate the population of our globe at 1,000,000,000 of 

 men; and the entire animal creation at three times this 

 number ; then, knowing the effect of the respiration of a 

 single man upon the oxygen of the air in a given time, it is 

 easy to calculate the action of the entire animal creation, 

 according to this computation, upon the total amount of 

 oxygen in our air. But who can undertake to determine, 

 with any show of probable correctness, at what sum the 

 entire amount of the brute creation is to be estimated — 

 quadrupeds and birds, and fishes and insects innumerable, on 

 the earth, and under the earth, and in the waters ? Moreover, 

 even supposing the correctness of their calculations, we must 

 remember that animal respiration is merely one amongst 

 many other changes which are constantly going on in the 

 material world, the effect of which is to cause the removal 

 of uncorabined oxygen, and the development of carbonic 

 acid. The principal material, in the various substances 

 made use of as fuel, is either carbon, or some compound 

 containing a large proportion of this element ; and its com- 

 bustion consists in a rapid combination with oxygen, by 

 which this gas is converted into the carbonic acid, attended 

 with the development of an elevated temperature. When 

 we consider to what a great extent the combustion of coal 

 is constantly going on in a manufacturing country like this 

 in which we live, (that is, how rapidly the carbon of the 



