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those by which they perpetuate their species ; 

 and those by which they are at length overtaken 

 by death, and reduced to the state again of mere 

 mineral matter. 



With respect to the first series of actions, all 

 organic substances possess the power of taking 

 from the external world certain solid arid liquid 

 matters, which they assimilate to their own na- 

 ture, and thus repair the waste which they are 

 continually undergoing ; and it is to this renewal 

 of their blood from without that digestion is in- 

 strumental. Further, they have the power of 

 effecting a motion of this blood between the in- 

 terstices of their solid parts, constituting the 

 function of circulation ; the ultimate object of 

 which is, the continual conversion of a portion 

 of this blood into the several tissues and secreted 

 fluids, and reciprocally the continual reconver- 

 sion of these tissues, as well as of such of the 

 fluids which are not evacuated from the body, 

 into blood, in which motions consist the func- 

 tions respectively of nutrition and secretion, and 

 of absorption. Lastly, they have the power of 

 taking from the external world certain aeriform, 

 as well as solid and liquid substances, while they 

 give off others, for the purification of their blood, 

 vitiated as it is by the processes just mentioned ; 

 tind it is to this interchange that respiration con- 

 duces. 



These continual revolutions are so character- 

 istic of organized beings, that by some life is 

 described as essentially consisting in them : " La 



