COMPARISON BETWEEN ANIMALS AND PLANTS. 337 



when animal substances are burning, similar to what we per- 

 ceive in the combustion of bones ; but nitrogen having been 

 discovered in some vegetables, this proof is no longer consider- 

 ed infallible. 



It appears then from a comparison between . animals and 

 vegetables, that these beings are closely connected by the 

 essential characters of organization ; that it seems impossible 

 to distinguish them by any trait that belongs exclusively to 

 either ; that the connexion between them appears the most 

 striking in the least perfect species of both kingdoms ; and that 

 as we recede from this point, the differences become more nu- 

 merous and more marked. 



We may illustrate this view, by imagining two ascending 

 chains, rising from one common point, each side of the chain 

 becoming more and more unlike in proportion to the interven- 

 ing distance from the centre. From this same central point, 

 also proceeds the chain of inorganized substances ; some im- 

 perfect animals resembling plants in their outward form, some, 

 both of animals and plants, resembling minerals in their hard 

 and calcareous coverings and shapeless forms. 



Having thus learned Jihe almost imperceptible gradations, 

 by which the animal and vegetable kingdoms are blended, we 

 must, in stating the important differences which exist between 

 animals and plants, consider the imperfect species of both 

 kinds, as exceptions to any general rule, and confine ourselves 

 to perfect animals and plants. 



1st. Plants differ from animals with respect to the elements 

 which compose them ; carbon, hydrogen and oxygen, form the 

 base of vegetable substances ; animals exhibit the same elements 

 with this i?nportant distinction, that carbon prevails in plants, 

 and nitrogen in animals. 



2d. They differ in their food; plants are nourished with in- 

 organized matter, absorbed with water, the various substances 

 which this liquid holds in solution ; animals are mostly nourished 

 either by vegetables or other animals. 



3d. Plants throw off oxygen gas, and inhale carbonic acid ; 

 animals in respiration inhale oxygen gas, and throw off carbonic 

 acid. 



4th. Although plants and animals both possess a principle of 

 life, it is in the one case much more limited than in the other ; ex- 

 hibiting itself in plants by a feeble power of contraction or irri- 

 tability ; in animals appearing in sensation, muscular movement 

 and voluntary motion. 



We see then, many important differences between perfect 



Result of the comparison between animals and vegetables Chains of beings 

 proceeding from one point Differences between animals and plants. 

 29 



