648 OF THE FUNCTIONS OF THE NERVOUS SYSTEM. 



Sensory G-anglia, may be considered, in common with the Cerebrum, as a true 

 and independent centre of nervous power, yet this independence is only mani- 

 fested when these organs are separated from each other, either structurally by 

 actual division, or functionally by the suspension of the activity of other parts. 

 In their state of perfect integrity and complete functional activity, they are all 

 (at least in Man) in such subordination to the Cerebrum, that they only minister 

 to its actions, except in so far as they are subservient to the maintenance of the 

 organic functions, as in the automatic acts of breathing and swallowing. "With 

 regard to every other action, the Will, if it possess its due predominance, can 

 exercise a determining power ; keeping in check every automatic impulse, and 

 even repressing the promptings of emotional excitement. And this seems to 

 result from the peculiar arrangement of the nervous apparatus ; which causes the 

 excitor impression to travel in the upward direction, if it meet with no inter- 

 ruption, until it reaches the Cerebrum, without exciting any reflex movements 

 in its course. When it arrives at the Sensorium, it makes an impression on the 

 consciousness of the individual, and thus gives rise to a sensation ; and the change 

 thus induced, being further propagated from the sensory ganglia to the Cerebrum, 

 becomes the occasion of the formation of an idea. If with this idea any pleasur- 

 able or painful feeling should be associated, it assumes the character of an emo* 

 tion; and either as a simple or as an emotional idea, it becomes the subject of 

 intellectual operations, whose final issue is in a volitional determination, or acfc 

 of the Will, which may be exerted in producing or checking a muscular move-* 

 ment, or in controlling or directing the current of thought. 



683. But if this ordinary upward course be anywhere interrupted, the im- 

 pression will then exert its power in a transverse direction, and a " reflex" ac- 

 tion will be the result, the nature of this being dependent upon the part of the 

 Cerebro-Spinal axis at which its ascent had been checked. Thus, if the inter- 

 ruption be produced by division or injury of the Spinal Cord, so that its lower 

 part is cut-off from communication with the encephalic centres, this portion then 

 acts as an independent centre, and impressions made upon it through the afferent 

 nerves proceeding to it from the lower extremities, excite violent reflex move- 

 ments, which, being thus produced without sensation, are designated as " excito- 

 motor." So, again, if the impression should be conveyed to the Sensorium, but 

 should be prevented by the removal of the Cerebrum, or by its state of func- 

 tional inaction, or by the direction of its activity into some other channel, from 

 calling forth ideas through its instrumentality, they may react upon the motolr 

 apparatus by the " reflex" power of the Sensory ganglia themselves ; as seems 

 to be the case with regard to those locomotive actions which are maintained 

 and guided by sensations during states of profound abstraction, when the atten- 

 tion of the individual is so completely concentrated upon his own train of thought 

 that he does not perceive external objects, although his movements are obviously 

 guided through the visual and tactile senses. Such actions, being dependent 

 upon the prompting of sensations, are "sensori-motor" or " consensual." But 

 further, there is evidence that even the Cerebrum may respond (as it were) au- 

 tomatically to impressions fitted to excite it to "reflex" action, when from any 

 cause the Will is in abeyance, and its power cannot be exerted either over the 

 muscular system or over the direction of the thoughts. Thus in the states of 

 Dreaming, Somnambulism, and even Reverie, whether spontaneous or artificially 

 induced (Sect. 7), ideas which take possession of the mind, and from which it 

 cannot free itself, may excite respondent movements; and this may happen also 

 when the force of the idea is morbidly exaggerated, and the will is not suspended 

 but merely weakened, as in many forms of Insanity. With these ideas, more- 

 over, Emotional states may be mixed up, and even Intellectual processes may be 

 prompted by them; so long, however, as these psychical operations take place at 

 the mere suggestion of antecedent impressions (the particular changes which these 



