46 



the several functions performed by organized be- 

 ings, and of the relations in which these stand 

 to each other. I have already alluded, while 

 speaking of the characteristic actions of ani- 

 mals, to those by which they renew their blood, 

 by assimilating to their own nature solid and 

 liquid substances received from without ; those 

 by which they circulate this blood ; those by 

 which they deposite from the blood the various 

 tissues and secreted fluids, in proportion as they 

 have been removed ; those by which they receive 

 again into the blood such tissues and fluids as 

 have become useless ; those by which they purify 

 the blood, as it becomes deteriorated in these 

 processes, by the reciprocal expulsion from it, 

 and reception into it, of certain aeriform mat- 

 ters ; and lastly, those by which they renew their 

 species. These include, as I remarked, the func- 

 tions of digestion, circulation, nutrition and se- 

 cretion, absorption, respiration and generation. 



A function may be defined to be the proper 

 action of a living organ, or set of living organs, 

 conducive to some definite end in the animal 

 economy. It is therefore quite distinct from a 

 property, such as that of excitability, or a power ; 

 such as those which call excitability into action ; 

 since it signifies such properties and powers in 

 mutual co-operation. Every action of every in- 

 dividual organ of the animal body is its function, 

 and the due performance of this is the only end 

 of its existence ; but the functions, collectively 



