INTRODUCTION. 13 
the principal parts. To assimilate them to their own compo- 
sition, they must get rid of the superabundant hydrogen and 
carbon in particular, and accumulate more azote, which is 
performed through the medium of respiration, by which the 
oxygen of the atmosphere combines with the hydrogen and. 
earbon 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, seems always to remain there. 
The relations of vegetables and animals to the surrounding 
atmosphere are therefore in an inverse ratio—the former re- 
ject water and carbonic acid, while the latter produce them. 
The essential function of the animal body is respiration, it is 
that which in a manner animalizes it, and we shall see that 
the animal functions are the more completely exercised, in 
proportion to the greatness of the powers of respiration pos- 
sessed by the animal. ‘This difference of relations constitutes 
the fourth character of animals. 
Of the forms peculiar to the Organic Elements of the Ani- 
mal Body, and of the principal combinations of its Che- 
mical Elements. 
An areolar tissue and three chemical elements are essential 
to every living body; there is a fourth element peculiarly re- 
quisite to that of an animal; but this tissue is composed of 
variously formed meshes, and these elements are variously 
combined. 
There are three kinds of organic materials or forms of tex- 
ture, the cellular membrane, the muscular fibre, and the me- 
dullary matter, and to each form belongs a peculiar combina- 
~ tion of chemical elements, as well as a particular function. 
i 
The cellular substance is composed of an infinity of small 
fibres and lamine, fortuitously disposed, so as form little cells 
that communicate with each other. It is a kind of sponge, 
which has the same form as the bedy, all other parts of which 
traverse or fill it, and contracting indefinitely, on the removal 
of the causes of its tension. It is this power that retains the 
wbggy' in a given aay and within certain limits. 
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’ “a roby be” 
