ANIMAL AND VEGETABLE KINGDOMS. 185 



continental island represent, as it were, the other orders 

 of Mammalia, under their special structural modifications. 

 New Holland appears thus as a continent with the cha- 

 racters of an older geological age. No one can fail, there- 

 fore, to perceive of how great an interest for Classification 

 will be a more extensive knowledge of the geographical 

 distribution of animals in general, and of the structural 

 peculiarities exhibited by localized types. 



SECTION XXIX. 



MUTUAL DEPENDENCE OF THE ANIMAL AND VEGETABLE KINGDOMS. 



Though it had long been known, by the experiments of 

 De Saussure, that the breathing process is very different 

 in animals and plants, and that while the former inhale 

 atmospheric air and exhale carbonic acid gas, the latter 

 appropriate carbon and exhale oxygen, it was not until 

 Dumas and Bousingault 1 particularly called the attention 

 of naturalists to the subject, that it was fully understood 

 how direct is the dependence of the animal and vege- 

 table kingdoms one upon the other in that respect, or 

 rather how the one consumes what the other produces, and 

 vice versa, thus tending to keep the balance, which either 

 of them singly would disturb to a certain degree. The 

 common agricultural practice of manuring exhibits on 

 another side the dependence of one kingdom upon the 

 other : the undigested particles of the food of animals 

 return to the ground to fertilize it for fresh production. 2 

 Again, the whole animal kingdom is either directly or 

 indirectly dependent upon the vegetable kingdom for its 



1 DUMAS, Le9on sur la statique chi- p. 122. 



rnique des etres organises, Ann. Sc. 2 LIEBIG, Agricultural Chemistry; 

 Nat., 2de ser., vol. 6, p. 33; vol. 17, Auiinal Chemistry. 



