ray 
Botany and Zoology. A29 
of oxygen gas by plants may be estimated by supposing existing vege- 
tation to cease evolving free oxygen, or (which would come to the same 
thing) by supposing some new operation in the organic world to absorb 
this element as fast as it is given to the air by plants. How soon 
would the diminution of the oxygen of the air be felt even by the 
higher classes of animals. Making the needful calculations, M. Duma 
has answered this question, by assuring us that the unbalanced action 
of the whole animal kingdom for a century would not consume more 
Nn gopo part by weight of the oxygen of the atmosphere ;—‘a 
quantity altogether inappreciable to the most delicate means of investi- 
gation we possess at the present day, and which very certainly would 
have no influence on the life of animals,”—that, as respects the higher 
races of animals, “it would require no less than 10,000 years before 
all the men on the face of the globe could produce an effect which 
should be sensible to Volta’s Eudiometer, even supposing vegetable life 
to be extinct during the whole of this time ;”—so vast is the original 
stock of this important element of the atmosphere. 
Surely, then, we ought not to call this remotely needful action upon 
the air the essential office of vegetables in the economy of the world, 
nor view as a subordinate or concomitant end that operation of organi- 
zing matter, which provides the whole animal creation with sustenance, 
and the failure of which for a single year would depopulate the earth. 
Nor should we call that the essential office of vegetation which certainly 
to the existence of man. ; 
Of course there is no question here of this as a function of vegeta- 
