668 FUNCTIONS OF THE CEREBRO-SPINAL NERVOUS SYSTEM. 



result of an accident occurring in childhood, which left him for some time 

 in a state of extreme debility ; and when he made the attempt to speak, it 

 was with considerable pain in the vocal organs. This pain probably re- 

 sulted from the unaccustomed effort which it was necessary to make, when 

 the usual guidance was wanting ; being analogous to the uneasiness which 

 we experience, when we attempt to move our eyes with the lids closed. His 

 voice at that time is described as being very similar to that of a person born 

 deaf and dumb, but who has been taught to speak. With the uneasiness in 

 the use of the vocal organs, was associated an extreme mental indisposition 

 to their employment ; and thus, for some years, the voice was very little ex- 

 ercised. Circumstances afterwards forced it, however, into constant em- 

 ployment ; and great improvement subsequently took place in the power of 

 vocalization, evidently by attention to the indications of the muscular sense. 

 It is a curious circumstance fully confirming this view, that the words which 

 had been in use previously to the supervention of the deafness, were still pro- 

 nounced (such of them, at least, as were kept in employment) as they had 

 been in childhood ; the muscular movements concerned in their articulation 

 having still been guided by the original auditory conception, in spite of the 

 knowledge derived from the information of others that such pronunciation 

 was erroneous. On the other hand, all the words subsequently learned were 

 pronounced according to their spelling ; the required associations between 

 the muscular sensations and the written signs being in this case the obvious 

 guide. 



538. It is through the "muscular sense," in combination with the visual 

 and tactile, that those movements are regulated which are concerned alike 

 in ordinary progression, and in the maintenance of the equilibrium of the 

 body. That the visual sense has, in most persons, a large share in this 

 regulation, is evident from the simple fact, that no one who has not been 

 accustomed to the deprivation of it, can continue to walk straight forwards, 

 when blindfolded, or in absolute darkness, towards any point in the direc- 

 tion of which he may have been at first guided. But the blind man, who 

 has been accustomed to rely exclusively upon his muscular sense, has no dif- 

 ficulty in keeping to a straight path ; and moves onwards with a confidence 

 which is in remarkable contrast with the gait of a man who has been de- 

 prived of sight for the occasion only. In fact, as Mr. Mayo has well re- 

 marked, 1 in our ordinary movements, "we lean upon our eyesight as upon 

 crutches."- -When our vision, however, instead of aiding and guiding us, 

 brings to the mind sensations of aij antagonistic character, our movements 

 become uncertain, from the loss of that power of guidance and control over 

 them which the harmony of the two sensations usually gives. Thus a person 

 unaccustomed to look down heights, feels insecure at the top of a tower or a 

 precipice, although he know* that his body is properly supported ; for the 

 void which he sees below him contradicts (so to speak) the tactile sensations 

 by which he is made conscious of the due equilibrium of his body. So, 

 uisiin, although any one can walk along a narrow plank, which forms part 

 of the floor of a room, or which is elevated but a little above it, without the 

 least difficulty, and even without any consciousness of effort, if that plank 

 be laid across a chasm, the bottom of which is so far removed from the eye 

 that the visual sense gives no assistance, even those who have braced their 

 nerves against all emotional distraction, feel that an effort is requisite to 

 maintain the equilibrium during their passage over it ; that effort being 

 aided by the withdrawal of the eyes from the abyss below, and the fixation 

 of them on a point beyond, which at the same time helps to give steadiness 



1 Outlines of Physiology, 3d edit., p. 345. 



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