b INTRODUCTION. 



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 

 maintenance 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 laminse, within whose 

 interstices are contained the fluids ; it is in these fluids that 

 the motion is most continued and extended. Foreign suId- 

 stances penetrate the body and unite with them ; they nourish 

 the solids by the interposition of their molecules, and also de- 

 tach from them those that are superfluous. 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 the fluids, and by their contraction communicate to 

 them part of their motion. 



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

 molecules, required considerable afiinity in their chemical' 

 composition ; and such is the fact the solids of organized bo- 

 dies 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 tis- 

 sue, whose more or less flexible fibres or laminse intercept fluids 

 more or less abundant j constitutes what is called the organi- 

 zation. 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 aiTange- 

 ments, which are all conditions of life ; and it is easy to con- 

 ceive, that if its effect be to alter either of these conditions, so 



