NATURE OF LIFE. 81 



Such a kind of composition, and such an arrangement of 

 the constituent parts, is called organization ; and as the vital 

 phenomena are only such motions as are consistent with 

 these material arrangements, life, so far as our experience 

 goes (and we have no other guide in these matters), is ne- 

 cessarily connected wit): organization. Life presupposes 

 organization, as the movements of a watch presuppose the 

 wheels, levers, and other mechanism of the instrument. 



The organization assumes certain definite forms in each 

 kind of animals ; not merely in the external arrangement 

 of the whole, but in each part, and in all the details of each. 

 On this depends the kind of motion which each part can ex- 

 ercise — the share which it is capable of contributing to the 

 general vital movement ; which latter, or, in short, life, is 

 the result of the mutual actions and re-actions of all parts. 



Living bodies exhibit a constant internal motion, in 

 which we observe an uninterrupted admission and assimila- 

 tion of new, and a correspondent separation and expulsion 

 of old particles. The form remains the same ; the compo- 

 nent particles are continually changing. While this motion 

 lasts, the body is said to be alive ; — when it has irrecover- 

 ably ceased, to be dead. The organic structure then yields 

 to the chemical affinities of the surrounding agents, and is 

 speedily destroyed. 



All living beings have, in the first place, formed part of 

 a body like their own ; have been attached to a parent be- 

 fore the period of their independent existence. The new 

 animal, while thus connected, is called a germ : its separa- 

 tion constitutes generation or birth. After this, it increases 

 in size according to certain fixed laws for each species and 

 each part. 



The duration of -existence is limited in all animals : after 

 a longer or shorter period, the vital movements are arrested, 

 and their cessation or death seems to occur as a necessary 

 consequence of life. 



Thus, then, absorption, assimilation, exhalation, genera- 

 tion and growth^ are functions common to all living beings; 

 birth and death, the universal limits of their existence ; a 



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