12 INTRODUCTION. 
which their nutritive fluid penetrates all other parts througts 
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 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 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 
. A 
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Nag 
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