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CHAPTER VIII. 



PHYSIOLOGICAL FUNCTIONS OF ANIMALS AND PLANTS. 



As has been before remarked, all the vital processes of ani- 

 mals and plants may be considered under three heads : i. 

 Functions of Nutrition, comprising all those functions where- 

 by the individual organism lives, grows, and maintains its 

 existence against all the hostile forces constantly at work 

 upon it. 2. Functions of Reproduction, comprising those 

 functions whereby the perpetuation of the species is secured, 

 while the individual perishes. 3. Functions of Relation, com- 

 prising all those functions, such as sensation and locomo- 

 tion, whereby the organism is brought into relation with the 

 outer world, and the outer world in turn reacts upon the 

 organism. 



In plants the functions of relation are reduced to their 

 minimum, and hence these functions are often spoken of as 

 the Animal functions ; whilst the functions of nutrition and 

 reproduction, as being common to all organisms, are 

 grouped together under the name of the Organic or Vegeta- 

 tive functions. Plants, however, are by no means wholly 

 destitute of the functions of relation ; and, curiously enough, 

 these functions are most developed, or, at any rate, most 

 conspicuous, in some of the lowest members of the vegetable 

 kingdom, which have on this account been mistaken for 

 animals. 



