FUNCTIONS OF THE SENSORY GANGLIA. G65 



house inaudible to others, the slightest rattle in the lock of a door, tearing 

 a morsel of paper, and a thousand little sources of sound not to be cata- 

 logued, induce results similar to those of visual impressions." 1 



534. It is, however, when the Cerebrum is not in a state which renders 

 it capable of receiving and acting upon Censorial impressions, that we find 

 the independent reflex activity of the Sensory ganglia most strikingly dis- 

 played. Thus in the Infant for some time after its birth, it is obvious to an 

 attentive observer, that a large part of its movements are directly prompted 

 by sensations to which it can as yet attach no distinct ideas, and that they 

 do not proceed from tlaat purposive impulse which is essential to render them 

 voluntary. This is well seen in the efforts which it makes to find the nipple 

 with its lips; being probably guided thereto at first by the smell, but after- 

 wards by the sight also ; when the nipple has been found, the act of suction 

 is purely excito-motor, as already explained. So in the Idiot whose brain 

 has never attained its normal development, the influence of sensations- in in- 

 directly producing respondent movements is obvious to all who examine his 

 actions with discrimination ; and a remarkable case has been described, 2 in 

 which an entire, though temporary suspension of Cerebral power, reducing 

 the subject of it to the condition of one of the lowest Vertebrata, gave a 

 very satisfactory proof of the independent action of this division of the 

 Encephalic centres. 



535. But we do not require to go so far in search of characteristic exam- 

 ples of this kind of reflex action ; since they are afforded by the perform- 

 ance of habitual movements, which ai~e clearly under Sensorial guidance, 

 when the Cerebrum is occupied in some train of action altogether discon- 

 nected with them. An individual who is subject to " absence of mind," 

 may fall into a reverie whilst walking the streets; his attention may be en- 

 tirely absorbed in a train of thought, and he may be utterly unconscious of 

 any interruption in its continuity ; and yet during the whole of that time 

 his limbs shall have been in motion, carrying him along the accustomed, 

 path, whilst his vision shall have given to those movements the direction' 

 which is requisite to guide him along a particular line, or to move him out 

 of it for the avoidance of obstacles. As already pointed out ( 510), there 

 seems strong reason for regarding the ambulatory movements of the limbs. 

 a.< in themselves excito-motor; but the guidance of these movements by the 

 visual sense indicates the participation of the Sensorium in this remarkable 

 performance. It has been maintained by some Metaphysicians and Physi- 

 ologists, that these "secondarily automatic" actions always continue to be 

 voluntary, because their performance is originally due to a succession of vo- 

 litional acts, and because, in any particular case, it is the Will which first 

 excites them, whilst an exertion of the Will serves to check them at any 

 time. But this doctrine involves the notion that the Will is in a state of 

 pendulum-like oscillation between the train of thought and the train of 

 movement; whereas nothing is more certain to the individual who, is the 

 subject of both, than that the former may be as uninterrupted as if the body 

 were perfectly at rest, and his reverie were taking place in the quietude of 

 his own study. And as it commonly happens that the direction taken is 

 that in which the individual is most in the habit of walking, it will not uu- 

 frequently occur that if he had previously intended to pursue some other, 

 he finds himself, when his reverie is at an end, in a locality which may be 

 very remote from that towards which his walk was originally destined ; 

 which would not be the case, if his movements had been still under the pur- 

 posive direction of the will. And although it is perfectly true that these 



1 Lancet, Oct. 4th, 1845. 2 Ibid., Nov. loth and 29th, 1845. 



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