8 PRINCIPLES OF BOTANY. 



indeed, there is no difficulty in pointing out numerous 

 lines of demarcation between the two kingdoms; but, as 

 we descend in the scale of each, we find an increasing 

 similarity in external characters, and a closer approxi- 

 mation between the analogies existing in many of 

 those functions which mark the presence of the living 

 principle, both in the animal and in the vegetable king- 

 doms. Perhaps, until the contrary shall be distinctly 

 proved, we may consider the superaddition of " sen- 

 sibility" to the living principle as the characteristic 

 property of animals ; a quality by which the individual 

 is rendered conscious of its existence or of its wants, 

 and by which it is induced to seek to satisfy those wants 

 by some act of volition. It has been supposed and 

 both analogy and experiment appear most fully to con- 

 firm the supposition that a sense of pain is very nearly, 

 if not entirely, absent in the inferior tribes of animals. 

 Even in the higher tribes, certain parts of the body are 

 incapable of receiving pain ; and there seems to be no 

 absurdity in considering that an animal may be endowed 

 with just so much sensibility as may be sufficient to 

 prompt it to select its food, though at the same time its 

 body may be so organised as to be incapable of transmitting 

 painful sensations. But the most constant, if not uni- 

 versal .distinction, and one which we can readily appre- 

 ciate, between animals and vegetables, consists in the 

 presence or absence of those internal sacs or stomachs, 

 with which the former alone are provided, for receiving 

 their food in its crude state, previously to its being 

 elaborated by the organs of nutrition. 



