10 FINAL CAUSES. 



dissipated faster than they can he renewed ; the 

 channels through which they circulate are more 

 and more obstructed, and at length cease to be per- 

 vious ; and the solids gradually become hard and 

 rigid. As in a machine of which the wheels are 

 worn, and the springs have lost their elastic force, 

 so in the animal body, at an advanced age, the 

 slightest additional impediment that occurs will 

 stop the movements of the whole system : and, when 

 once stopped, their renewal is impossible. Nature 

 has thus assigned to every living being a certain 

 period as the utmost extent of its duration. Even 

 when exempt from external interference, all are 

 doomed to perish, sooner or later, by the slow but 

 unerring operation of the same internal causes 

 which originally effected their developement and 

 growth, and which are inseparably interwoven with 

 the conditions of their existence. 



Numerous, however, are the extraneous and ac- 

 cidental causes which may hasten or precipitate 

 their destruction, long before the period of natural 

 decay. How striking is the contrast, on those oc- 

 casions, between the scene w^e have just beheld of 

 an animal in the full vigour of its powers, either 

 rapidly bounding across the plain, or gliding be- 

 neath the wave, or soaring in the elevated regions 

 of air, and the spectacle of the same animal lying, 

 the next moment, extended at our feet, bereft at 

 once of activity and of sense — of all the faculties 

 and powers that constitute life. Can we contem- 

 plate without amazement so complete and instanta- 

 neous a change ; so sudden and awful a catastrophe? 

 Shall we not be animated by an eager desire to 

 penetrate so great a mystery, and resolve the many 



