CHAPTER THIRD. 



FUNCTIONS AND ORGANS OF ANIMAL, LIFE. 



SECTION I. 



OF THE NERVOUS SYSTEM AND GENERAL SENSATION. 



59. LIFE, in animals, is manifested by two sorts of func- 

 tions, viz. : First, the peculiar functions of animal life, or 

 those of relation, which include the functions of sensation 

 and voluntary motion ; those which enable us to approach, 

 and perceive our fellow beings and the objects about us, and 

 to bring us into relation with them : Second, the functions 

 of vegetative life, which are nutrition in its widest sense, 

 and reproduction ; * those indeed which are essential to the 

 maintenance and perpetuation of life. 



60. The two distinguishing characteristics of animals, 

 namely, sensation and motion, (57,) depend upon special 

 systems of organs, which are wanting in plants, the nervous 

 system and the muscular system under its influence. The 

 nervous system, therefore, is the grand characteristic of the 

 animal body. It is the centre from which all the commands 

 of the will issue, and to which all sensations tend. 



* This distinction is the more important, inasmuch as the organs of 

 animal life, and those of vegetative life, spring from very distinct layers 

 of the embryonic membrane. The first are developed from the upper 

 layer, and the second from the lower layer of the germ of the animal. 

 See Chapter on Embryology, p. 112. 



