168 ANIMALS AND PLANTS vi 



hand, the definition thus amended will exclude all 

 ordinary vegetable organisms. 



Cuvier himself practically gives up his second 

 distinctive mark when he admits that it is want- 

 ing in the simpler animals. 



The third distinction is based on a completely 

 erroneous conception of the chemical differences 

 and resemblances between the constituents of 

 animal and vegetable organisms, for which Cuvier 

 is not responsible, as it was current among con- 

 temporary chemists. It is now established that 

 nitrogen is as essential a constituent of vegetable 

 as of animal hving matter ; and that the latter is, 

 chemically speaking, just as complicated as the 

 former. Starchy substances, cellulose and sugar, 

 once supposed to be exclusively confined to plants, 

 are now known to be regular and normal products 

 of animals. Amylaceous and saccharine substances 

 are largely manufactured, even by the highest 

 animals ; cellulose is widespread as a constituent 

 of the skeletons of the lower animals ; and it is 

 probable that amyloid substances are universally 

 present in the animal organism, though not in the 

 precise form of starch. 



Moreover, although it remains true that there 

 is an inverse relation between the green plant in 

 sunshine and the animal, in so far as, under these 

 circumstances, the green plant decomposes car- 

 bonic acid and exhales oxygen, while the animal 

 absorbs oxygen and exhales carbonic acid ; yet 



