12 INTRODUCTION. 



which their nutritive fluid penetrates all other parts through 

 pores or vessels, which are a kind of internal roots. 



The organization of this cavity and its appurtenances re- 

 quired varying, according to the nature of the aliment, and 

 the operation it had to undergo, before it could furnish juices 

 fit for absorption; whilst the air and earth present to ve- 

 getables 'nought but elaborated juices ready for absorption. 



The animal, whose functions are more numerous and varied 

 than those of the plant, consequently necessitated an organiza- 

 tion much more complete ; besides this, its parts not being 

 capable of preserving one fixed relative position, there were 

 no means by which external causes co\ild produce the motion 

 of their fluids, which required an exemption from atmospheric 

 influence ; from this originates the second character of animals, 

 their cii^culating system^ one less essential than that of diges- 

 tion, since in the more simple animals it is unnecessary. The 

 animal functions required organic systems, not needed by ve- 

 getables that of the muscles for voluntary motion, and nerves 

 for sensibility ; and these two systems, like the rest, acting only 

 through the motions and transformations of the fluids, it was 

 necessary that these should be most numerous in animals, and 

 that the chemical composition of the animal body be more com- 

 plex than that of the plant; and so it is, for one substance more 

 (azote) enters into it as an essential element, whilst in plants 

 it is a mere accidental junction with the three other general 

 elements of organization, oxygen, hydrogen, and carbon. 

 This then is the third character of animals. 



From the sun and atmosphere, vegetables receive for their 

 nutrition water, which is composed of oxygen and hydrogen ; 

 air, which contains oxygen and azote ; and carbonic acid, which 

 is a combination of oxygen and carbon. To extract their 

 own composition from these aliments, it was necessary they 

 should retain the hydrogen and carbon, exhale the super- 

 fluous oxygen and absorb little or no azote. Such, in fact, is 

 vegetable life, whose essential function is the exhalation of 

 oxygen, which is effected through the agency of light. 



Animals also derive nourishment, directly or indirectly, 

 from the vegetable itself, in which hydrogen and carbon form 



