THE FUNCTIONS OF LIFE. 41 



elaboration in particular vessels and recep- 

 tacles — their deposition of solid materials — and 

 their conversion into peculiar products, as well 

 as into the substances which compose the several 

 organs ; — and, finally, the growth and develope- 

 ment of the whole plant. Still more various 

 and complicated are the corresponding functions 

 in animals. Their objects may be arranged 

 under the following general heads ; each, again, 

 admitting of further subdivision. The first end 

 to be accomplished is to animalize the food ; that 

 is, to convert it into a matter having the chemical 

 properties of the animal substances with which 

 it is to be afterwards incorporated. The entire 

 change thus effected is termed Assimilation, of 

 which Digestion forms a principal part. The 

 second object is to collect and distribute this 

 prepared nutriment, which is the blood, to the 

 different organs, or wherever it may be wanted* 

 The necessary motions for these purposes are 

 given to the blood by the organs of Circulation, 

 consisting of the Heart, which impels it through 

 a system of pipes called Arteries, 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 continually 

 undergo purification by the chemical action of 

 oxygen : a purpose which is answered by the 

 function of Respiration. The fourth stage of 

 nutrition relates to the more immediate appli- 



