DIVISIONS OF THE NERVOUS SYSTEM. 15 



2. The nervous system connects into a coordinated or- 

 ganism every part of the body. It is the medium through 

 which all impressions are received. It animates or regulates 

 all movements, voluntary and involuntary. It regulates the 

 functions of secretion, nutrition, calorification, and all the 

 processes of organic life. 



In addition to its functions as a medium of conduction 

 and communication, the nervous system, in certain -of its 

 parts, is capable of receiving impressions and of generating 

 a stimulating influence, or force, peculiar to itself. As there 

 can be no physiological connection or coordination of differ- 

 ent parts of the organism, having an active function, without 

 nerves, there can be no unconscious reception of impressions 

 giving rise to involuntary movements, no appreciation of 

 impressions, general, as in ordinary sensation, or special, as 

 in sight, smell, taste, or hearing, no instinct, volition, 

 thought, or even knowledge of existence, without nerve- 

 centres. * 



Possessing, as it does, these varied properties and func- 

 tions, it is evidently of the greatest physiological importance 

 that the anatomical characters of the nervous system should 

 be most carefully studied, with a view, if possible, of con- 

 necting certain of the nervous properties with peculiarities 

 in structure. It is also important to subdivide the system, 

 as regards general properties and functions, as well as with 

 reference to the special office of particular parts. With this 

 end in view, we will point out, first, the great anatomico- 

 physiological divisions common to nervous matter wherever 

 it exists, and afterward, the subdivisions of the system as re- 

 gards special functions. 



Divisions of the Nervous System. 



Nervous matter, whatever may be its special function, 

 presents two great divisions, each with distinct anatomical 



irritability," in treating of the properties of the muscles. See vol. iii., Move- 

 ments, p. 463. 



102 



