156 PHYSIOLOGICAL BOTANY. PART II. 



after having attained perfection, that they as gra- 

 dually decay, die, and are decomposed. In fact the 

 general phenomena of life and death, are scarcely less 

 striking in the vegetable than in the animal king- 

 dom ; and probably the vital principle, considered 

 apart from sensibility, is something of the same kind, 

 if not the very same thing, both in animals and vege- 

 tables. This similarity or unity in essence must lead 

 us to expect, what experience has shown to be the fact, 

 that a considerable analogy exists between the functions 

 of animal and vegetable life. Although every argu- 

 ment which may be derived from this analogy, cannot 

 be too severely scrutinised before we admit the particular 

 conclusion which it may seem to establish, yet we may 

 confidently reckon upon the certainty of its existence, as 

 one of the best guides which we now possess, towards 

 obtaining a more perfect elucidation of the general laws 

 of physiology. 



(140.) Vital Stimulants. Life, though at the best 

 of only temporary duration in organised bodies, cannot 

 be maintained in them at all, without the continued 

 application of certain stimulants. All require peculiar 

 kinds of food, according to their respective natures ; a 

 sufficiency of air, of moisture, of heat, &c. If entirely 

 deprived of these stimulants, they soon die ; and even 

 when they are only partially subjected to their influence, 

 in a less proportion than is requisite for a free exercise 

 of their functions, they languish and become sickly. 

 But, besides the various salutary influences to which 

 all living bodies must be submitted, in order to secure 

 for them a due and healthy performance of their 

 several functions, there are others to which they 

 may be subjected, which are decidedly noxious under 

 all conditions, and which must ultimately prove fatal 

 to them, if they had not the power of escaping from 

 their presence, or at least of modifying their effects. 

 In proportion as a living being possesses a greater 

 power of choice, either in profiting by those circum- 



