650 OF THE FUNCTIONS OF THE NERVOUS SYSTEM. 



reception of the impressions which excite the activity of the Hemispheric gan- 

 glia, and as the instrument whereby the results of their operation are brought 

 to bear upon the muscular system ; but that it is also the centre of reflexion 

 through which various automatic movements are called forth, that are immedi- 

 ately concerned in the maintenance of the organic functions. The impressions 

 which excite these movements do not in general pass on to the Cerebrum; for 

 we only perceive them when we specially direct our attention to them, or when 

 they exist in unusual potency. Thus we are unconscious of the "besom de re- 

 spirer" by which our ordinary movements of respiration are prompted ; and it is 

 only when we have refrained from breathing for a few seconds, that we experi- 

 ence a sensation of uneasiness which impels us to make forcible efforts for its 

 relief. Notwithstanding, however, that the Cerebrum is thus unconcerned in 

 the ordinary performance of these automatic movements, yet it can exert a 

 certain degree of control over many of them, so as even to suspend them for a 

 time; but in no instance can it carry this suspension to such an extent as 

 seriously to disarrange the organic functions ; thus, when we have voluntarily 

 refrained from breathing for a few seconds, the inspiratory impulse so rapidly 

 increases in strength with the continuance of the suspension, that it at last 

 overcomes the most powerful effort we can make for the repression of the move- 

 ments to which it prompts. Now in this and similar cases, it would seem as if 

 the Will interfered to prevent that direct transverse passage of the stimulus 

 from the afferent to the efferent nerves, through the Cranio-Spinal axis, which 

 constitutes the ordinary line of action for impressions having their origin in the 

 necessities of the organic or vegetative life of the individual. That the Will 

 should have a certain degree of control over these movements, is necessary in 

 order that they may be rendered subservient to various actions which are neces- 

 sary for the due exercise of Man's psychical powers ; but that they should not 

 be left dependent upon its exercise, and should even be executed in opposition 

 to it, when the wants of the system imperatively demand their performance, 

 constitutes a wise provision for securing Life against the chances of inattention 

 or momentary caprice. 



686. The general views here put forth in regard to the independent and con- 

 nected actions of the several primary divisions of the Cerebro-Spinal apparatus, 

 may perhaps be rendered more intelligible by the following Table, which is in- 

 tended to represent the ordinary course of operation when the whole is in a 

 state of complete functional activity ( 682), and the character of the "reflex" 

 actions to which each part is subservient, when it is the highest centre that the 

 impression can reach ( 683). 



WILL , 



Intellectual operations J "] 



1 ! 



Emotions __ 



centre of emotional and ideo-motor reflection 



Ideas 



Sensations ^-SENSORY GANGLIA 



centre of sensori-motor reflection 



Motor Imnulse. 



Impressions S3 >SPINAL CORD 



centre of excito-motor reflection 



