388 NERVOUS ACTION. 



In addition to those spoken of above, may be mentioned 

 physical nervous actions due to a morbid origin. Such are 

 the involuntary movements which sometimes take place 

 as a result of diseased conditions of the great nervous cen- 

 tres. These differ from those already noticed in not being 

 due to reflex action, and accordingly bear an analogy to 

 mental nervous actions. 



Besides the purely physical nervous acts, there is another 

 class of necessity connected with the mind, and hence termed 

 mental or psychical nervous actions. These are of three 

 kinds acts of perception, of emotion, and of volition. 1st, 

 Acts of perception include general and special sensibility, &c.; 

 an impression in this case is made on some part of the body, 

 and from that conveyed to the mind. 2d, Acts of volition, 

 in which any portion of the body is moved in obedience to 

 a mandate of the will : this, unlike the last, originates with 

 the mind, from which the necessary stimulus is conveyed 

 through the nervous system. 3d, Acts of emotion, with 

 * which we shall have less to do, are those actions which 

 originate in peculiar psychical conditions, as in joy, anger, 

 fear, &c., and which are in great part independent of the 

 will. 



In connection with the above mentioned functions, it 

 is worthy of note, that, of all the systems of the animal 

 body, the nervous alone is that upon which the mind can 

 directly act, or which can act immediately upon the mind. 

 This system, moreover, is peculiar to animals, and is a dis- 

 tinguishing characteristic of the latter, as compared with 

 the vegetable creation. In the words of Dr Todd, " it is 

 obviously the presence of a psychical agent, controlling 

 and directing certain bodily acts of animals, which has 

 called into existence the peculiar apparatus which the 

 nervous matter is employed to form." 



