INTRODUCTION. 
17 
faculty which certain corporeal combinations have, of enduring for a time, and under 
a determinate form, by incessantly attracting into their composition a part of sur- 
rounding substances, and rendering to the elements portions of their own proper 
substance. 
Life, then, is a vortex {tourhillon) , more or less rapid, more or less complicated, 
the direction of which is constant, and which always carries along molecules of 
the same kind, but into which individual molecules are continually entering, and 
from which they are constantly departing ; so that the form of a living body is more 
essential to it than its matter. 
As long as this movement subsists, the body in which it takes place is living — 
it lives. When it is permanently arrested, the body dies. After death, the elements 
which compose it, abandoned to the ordinary chemical affinities, are not slow to 
separate, from which, more or less quickly, results the dissolution of the body that 
had been living. It was then by the vital motion that its dissolution was arrested, and 
that the elements of the body were temporarily combined. 
All living bodies die after a time, the extreme limit of which is determined for each 
species ; and death appears to be a necessary consequence of life, which, by its own 
action, insensibly alters the structure of the body wherein its functions are exercised, 
so as to render its continuance impossible. 
In fact, the living body undergoes gradual but constant changes during the whole 
term of its existence. It increases first in dimensions, according to the proportions 
and within the limits fixed for each species, and for each of its several parts ; then 
it augments in density, in most of its parts : — it is this second kind of change that 
appears to be the cause of natural death. 
On examining the various living bodies more closely, a common structure is 
discerned, which a little reflection soon causes us to adjudge as essential to a vortex, 
such as the vital motion. 
Solids, it is evident, are necessary to these bodies for the maintenance of their 
forms, and fluids for the conservation of motion in them. Their tissue, then, is com- 
posed of interlacement and network, or of fibres and solid laminae, which inclose the 
liquids in their interstices : it is in these liquids that the motion is most continual and 
most extended ; the extraneous substances penetrate the intimate tissue of bodies in 
incorporating with them ; they nourish the solids by interposing their molecules, and 
also detach from them their superfluous molecules : it is in a liquid or gaseous form 
that the matters to be exhaled traverse the pores of the living body ; but, in return, it 
is the solids which contain these fluids, and by their contraction communicate to them 
a part of their motion. 
I’his mutual action of the solids and fluids, this passage of molecules from one to 
the other, necessitated considerable affinity in their chemical composition ; and, accord- 
ingly, the solids of organized bodies are in great part composed of elements easily 
convertible into liquids or gases. 
The motion of the fluids, requiring also a continually repeated action on the 
part of the solids, and communicating one to them, demanded of the latter both 
flexibility and dilatability ; and hence we find this character nearly general in all 
organized solids. 
This fundamental structure, common to all living bodies — this areolar tissue, the more 
c 
