

GENERAL CHARACTERS OP LIVING BKINCJS. 19 



before we quit these general views. The properties of organised 

 bodies require certain conditions for their operation. Thus, a 

 seed, which possesses vital properties in a dormant or inactive 

 condition, and which may retain these for hundreds or even 

 thousands of years, if placed in favourable circumstances so to do, 

 begins to germinate or grow, as soon as it is submitted to the 

 proper degree of warmth, moisture, and air. These, then, are 

 the conditions requisite for those changes which WQ call its Life ; 

 for the dry inactive seed can scarcely be said to be alive ; though, 

 on the other hand, it certainly is not dead, since it possesses 

 those properties or capabilities which enable it to live when placed 

 in favourable circumstances. Again, suppose a Plant to be 

 actively vegetating under the influence of light, warmth, and 

 moisture, und to be suddenly deprived of all these$ by being 

 carried, for example, into a cold dark cellar ; all its vital pro 

 cesses receive a check, and it either dies, or, if sufficiently hard} 

 to sustain the shock, it remains inactive until the necessary con 

 ditions of its growth be renewed. These conditions are techni- 

 cally called the stimuli to vital actions ; and thus we see that 

 Life is the result of the operation of these stimuli upon organised 

 structures possessed of peculiar properties. In attempting, 

 therefore, to understand the history of Vegetation, we have three 

 things to consider ; in the first place, the nature of the structure 

 of plants; next, the properties which their several kinds of struc- 

 ture respectively possess ; and lastly, the operation of various 

 external stimuli upon these properties, so as to produce vital 

 actions. 



10. In considering the history of Animal Life, exactly the 

 same course will be gone through ; but there will then be an 

 additional subject to be treated of ; namely the internal stimuli, 

 arising from the will of the being, which cause those actions that 

 are termed spontaneous, since they have no direct dependence 

 upon external stimuli, but originate in the animal itself. In the 

 history of Man, these actions evidently form a large part ; but in 

 the lowest animals they are very obscure, and can often scarcely 

 be distinguished from the actions of plants. But even in man 

 we have no difficulty in recognising a great number of actions 



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