44 THE FUNCTIONS OP LIFE. 



a system of pipes called Jirteries, and receives it back again 

 by means of another set of tubes called Veins, In the third 

 place it is necessary that the circulating blood should con- 

 tinually undergo purification by the chemical action of oxy- 

 gen: a purpose which is answered by the function of Res- 

 piratloii. The fourth stage of nutrition relates to the more 

 immediate application of this purified material to the wants 

 of the S3^stem, to the extention of the organs, to the repara- 

 tion of their losses, and to the restoration of their exhausted 

 powers. 



Life, then, consists of a continued series of actions and re- 

 actions, ever varying, yet constantly tending to definite ends. 

 Most of the parts of which the body consists undergo con- 

 tinual and progressive changes in their dimensions, figure, 

 arrangement, and composition. The materials which have 

 been united together and fashioned into the several organs, 

 are them.selves successively removed and replaced by others, 

 which again are, in their turn, discarded, and new materials 

 substituted, though without any perceptible change of ex- 

 ternal form. Perpetual mutation appears to constitute the 

 fundamental law of living nature; and it has been farther 

 decreed by the power which gave the first impulse of ani- 

 mation to this organized fabric, that its movements and its 

 powers shall be limited in their duration, and that, even 

 when they are not destroyed by extraneous causes, after 

 continuing for a certain period, they shall come to a close. 

 The law of Mortality, to which all the beings that have re- 

 ceived the gift of life are subjected, is a necessary conse- 

 quence of the law of mutation; and the same causes that 

 originally effected the development and growth of the sys- 

 tem, and maintained it in the vigour of its maturity, by con- 

 tinuing to operate, are certain to lead to the demolition of 

 the fabric they had raised, and to the exhaustion and final 

 extinction of its powers. The individual dies; but it is only 

 to give place to other beings, alike in nature and in form, 

 equally partaking of the blessings of existence, and destined, 

 after having, in their turn, given rise to a new race of sue- 



