INTRODUCTION. 17 



faculty which certain cor|ioreal comljinations 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 (iovrhillon), more or less rapid, more or less complicated, 

 the direction of whicli 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 matler. 



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, fi'om 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 j 



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, bj' its own j 



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 deatn. 



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 lamina, which inclose the 

 liquids in their interstices : it is in these hquids 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. 



This 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 

 Dart of the solids, and communicating one to them, demanded of the latter both 

 flexibility and dilatabihty ; and hence we find this character nearly general in ail 

 Drganized solids. 



This fundamental structure, common tu all living bodies — this areolar tissue, the more 



