24< INTRODUCTION. 



change themselves ; life presupposes their being, 

 for it can exist only in organized bodies prepared 

 for its action ; and neither the most profound medi- 

 tation, nor the most sedulous observations, have ever 

 been able to penetrate the mystery attached to the 

 pre-existence of germs. 



Division of organized beings into Animals and 

 Vegetables. 



Living or organized beings have, from the earliest 

 periods of observation, been divided into two king- 

 doms, the animal and the vegetable ; the first en- 

 dowed with the faculties of sense and motion, the 

 second destitute of both, and reduced to the mere 

 capacity of vegetation. Though the roots of vege- 

 tables are constantly directed to where moisture is 

 to be found, and the leaves toward the open air and 

 light ; though some plants seem instinctively to 

 withdraw from the touch, and oscillations may be 

 perceived in others, for which we can dicover no 

 external cause, yet are these various motions too 

 dissimilar to those of animals to afford any proof of 

 perception and volition. 



The spontaneous motion essential to animals re- 

 quires peculiar modifications even in such of their 

 organs as are purely vegetative. Unprovided with 

 roots to penetrate the soil, and constantly absorb 

 nutrition, other means were necessary of procuring 

 aliment from without, and a peculiar reservoir for 

 containing it within ; hence is derived the first lead- 



