10 INTRODUCTION. 



and earth present to vegetables nought but elaborated juices ready for 

 absorption. 



The animal, whose functions are more numerous and varied than 

 those of the plant, consequently required an organisation much more 

 complicated ; besides this, its parts not being capable of preserving one 

 fixed relative position, there were no means by which external causes 

 could produce the motion of their fluids, which required an exemption 

 from atmospheric influence ; from this originates the second character 

 of animals, their circulating system, one less essential than that of 

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

 functions required organic systems, not needed by vegetables that of 

 the muscles for voluntary motion, and nerves for sensibility ; and these 

 two systems, like the rest, acting only through the motions and trans- 

 formations of the fluids, it was necessary that these should be most 

 numerous in animals, and that the chemical composition of the animal 

 body should be more complex 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 organisation, 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 

 superfluous 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 the hydrogen and carbon form the principal 

 parts. To assimilate them to their own composition, they must get rid 

 of the superabundant hydrogen and carbon in particular, and accumu- 

 late more azote, which is performed through the medium of respiration, 

 by which the oxygen of the atmosphere combines with the hydrogen and 

 carbon of their blood, and is exhaled with them in the form of water and 

 carbonic acid. The azote, whatever part of the body it may penetrate, 

 geems always to remain there*. 



cem 

 lation. 



The experiment* of Dr. Edwards arc opposed to this opinion ; Dr. Edwards's inferences 

 i to render it probable that azote is absorbed, and again discharged fronj the circu- 



