16 INTRODUCTION. 



its tissue, has a form peculiar to itself, not merely general and exter- 

 nal, but extending to the detail of the structure of each of its parts; 

 and it is upon this form, which determines the particular direction of 

 each of the partial movements that take place in it, that depends the 

 complication of the general movement of its life— it constitutes its 

 species and renders it what it is. Each part co-operates in this 

 general movement by a peculiar action, and experiences from it 

 particular effects, so that in every being life is a whole, resulting from 

 the mutual action and re-action of all its parts. 



Life, then, in general, pre-supposes organization in general, and 

 the life proper to each individual being pre-supposes an organization 

 peculiar to that being, just as the movement of a clock pre-supposes 

 the clock; and accordingly we behold life only in beings that are 

 organized and formed to enjoy it, and ail the efforts of philosophy 

 have never been able to discover matter in the act of organization, 

 neither per se, nor by any external cause. In fact, life exercising 

 upon the elements which at every moment form a part of the living 

 body, and upon those which it attracts to it, an action contrary to 

 that which, without it, would be produced by the usual chemical 

 affinities, it seems impossible that it can be produced by these affini- 

 ties, and yet we know of no other power in nature capable of re- 

 uniting previously separated molecules. 



The birth of organized beings is, therefore, the greatest mystery 

 of the organic economy and of all nature: we see them developed, 

 but never being formed; nay more, all those whose origin we can 

 trace, have at first been attached to a body similar in form to their 

 own, but which was developed before them — in a word, to a parent. 

 So long as the offspring has no independent existence, but partici- 

 pates in that of its parent, it is called a germ. 



The place to which the germ is attached, and the cause which 

 detaches it and gives it an independent life, vary; but this primitive 

 adhesion to a similar being is a rule without exception. The sepa- 

 ration of the germ is called generation. 



Every organized being re-produces others that are similar to itself, 

 otherwise, death being a necessary consequence of life, the species 

 would become extinct. 



Organized beings have even the faculty of reproducing, in degrees 

 varying with the species, particular parts of which they may have 

 been deprived — this is called the power of reproduction. 



The development of organized beings is more or less rapid, and 



