INTRODUCTION. 15 



In fact, the living body undergoes gradual, but continual changes, 

 during the whole term of its existence. At first, it increases in 

 dimensions, according to proportions, and within limits, fixed for 

 each species and for each one of its parts; it then augments in den- 

 sity in the most of its parts: — it is this second kind of change that 

 appears to be the cause of natural death. 



If we examine the various living bodies more closely, we find they 

 possess a common structure, which a little reflection soon causes us 

 to perceive is essential to a vortex such as the vital motion. 



Solids, it is plain, are necessary to these bodies, for the mainte- 

 nance of their forms; and fluids for the conservation of motion in 

 them. Their tissue, accordingly, is composed of network and 

 plates, or of fibres and solid laminae, within whose interstices are 

 contained the fluids; it is in these fluids that the motion is most con- 

 tinued and extended. Foreign substances penetrate the body and 

 unite with them; they nourish the solids by the interposition of their 

 molecules, and also detach from them those that are superfluous. 

 It is in a liquid or gaseous form that the matters to be exhaled tra- 

 verse the pores of the living body; but in return, it is the solids which 

 contain the fluids, and by their contraction communicate to them 

 part of their motion. 



This mutual action of the fluids and solids, this transition of mole- 

 cules, required considerable affinity in their chemical composition; 

 and such is the fact — the solids of organized bodies being mostly 

 composed of elements easily convertible into fluids or gases. 



The motion of the fluids needing also a constantly repeated action 

 on the part of the solids, and communicating one to them, required 

 in the latter both flexibility and dilatability; and accordingly we find 

 this character nearly general in all organized solids. 



This structure, common to all living bodies; this areolar tissue, 

 whose more or less flexible fibres or laminae intercept fluids more or 

 less abundant; constitutes what is called the organization. As a 

 consequence of what we have said, it follows, that life can be enjoyed 

 by organized bodies only. 



Organization, then, results from a great variety of arrangements, 

 which are all conditions of life; and it is easy to conceive, that if its 

 effect be to alter either of these conditions, so as to arrest even one 

 of the partial motions of which it is composed, the general move- 

 ment of life must cease. 



Every organized body, independently of the qualities common to 



