22 INTRODUCTION. 



are centres penetrated by foreign substances which they appro- 

 priate to themselves, and from which issue others that become 

 foreign to them. In this movement of momentary formation, 

 the matter of the body changes continually, but its form still 

 remains. It is in the liquid state that foreign substances pene- 

 trate organized bodies ; it is also in the state of fluidity that 

 the superfluous molecules are cast off. The liquids and solids 

 are incessantly in motion during organization; the liquids tra- 

 versing the cavities of the solids, while the latter, by their 

 dilatation and contraction, produce the greater part of the 

 movement of the former. They continually change the con- 

 stituent parts of one into the other, part of the moving fluids 

 becoming for a time solids, while some solid parts are con- 

 verted again into liquids, which exchange perfectly agrees 

 with the analogy of their composition. Organized bodies ex- 

 perience changes during the whole course of their existence : 

 and from the moment of their origin they increase their di- 

 mensions and density. This latter kind of mutation contin- 

 ues until the structure of the body being insensibly altered, 

 the vital movement languishes and at last stops, which consti- 

 tutes death; after this, the elements which composed the or- 

 ganized body separate, and form new combinations. Each 

 organized body having not only its external form, but its 

 own peculiar structure, each of these parts contributes by its 

 action to the general result. The appellation of function is 

 given to the action of each organ, or to the combined actions 

 of several having the same end. 



Nutrition, a function comprising absorption, assimilation and 

 excretion, of which we have just spoken, is not the only phe- 

 nomenon common to organized bodies; generation is another 

 equally as general, and without which species could not exist, 

 death being the necessary consequence of life. Every organ- 

 ized and living body originates from one resembling itself, and 

 each produces its like. In order to accomplish this object, a 

 part of an organized body which had already attained its full 

 size, having received from it the materials for its own growth, 

 separates from it and produces a being in every respect similar 

 to its parent, and presenting the same phenomena. This part 



