INTRODUCTION. 9 



from the other, or from common parents, or from such as resemble them 

 as strongly as they resemble each other. But, although this definition 

 is strict, it will be seen that its application to particular individuals may 

 be very difficult, where the necessary experiments have not been made. 



Thus then it stands absorption, assimilation, exhalation, develop- 

 ment, and generation, are functions common to all living bodies ; birth 

 and death the universal limits of their existence ; a porous contractile 

 tissue, containing within its laminae, fluids or gases in constant motion, 

 the general essence of their structure ; substances almost all sus- 

 ceptible of conversion into fluids or gases, and combinations capable of 

 an easy and mutual transformation, being the basis of their chemical 

 composition. Fixed forms that are perpetuated by generation distin- 

 guish their species, determine the complication of the secondary functions 

 proper to each of them, and assign to them the parts they are to play on 

 the great stage of the universe. These forms are neither produced nor 

 changed by their own agency life supposes their existence ; its flame can 

 only be kindled in an organisation already prepared, and the most 

 profound meditation, and lynx-eyed and delicate observation, can 

 penetrate no farther than the mystery of the pre-existence of the germs. 



DIVISIONS OF ORGANISED BEINGS INTO ANIMALS AND VEGETABLES. 



Living or organised beings have always been subdivided into animate 

 beings, that is, such as are possessed of sense and motion ; and into 

 inanimate beings, which are deprived of both these faculties, and are 

 reduced to the simple faculty of vegetating. Although the leaves of 

 several plants shrink from the touch, and the roots are steadily directed 

 towards moisture, and the leaves to light and air ; and though parts of 

 vegetables appear to oscillate without any apparent external cause, still 

 these various motions have too little similarity to those of animals to 

 enable us to find in them any proofs of perception or will. 



The spontaneous motions of animals required essential modifi- 

 cations even in their purely vegetative organs. Their roots not 

 penetrating the earth, it was necessary they should be able to place 

 within themselves a supply of aliment, and to carry its reservoir along 

 with them. Hence is derived the first character of animals, or their 

 alimentary canal, from which their nutritive fluid penetrates all other 

 parts through pores or vessels, which are a kind of internal roots. 



The organisation of this cavity and its appurtenances required vary- 

 ing, according to the nature of the aliment and the operation it had to 

 undergo, before it could furnish juices fit for absorption ; whilst the air 



