TOUCH. 



1173 





cular sense" may be made good by the visual; 

 thus, the patient who cannot walk, because he 

 cannot feel either the contact of his foot with 

 the ground, or the muscular effort he is mak- 

 ing, can do so if he looks at his limbs ; and the 

 woman who cannot feel the pressure of her 

 child upon her arms, can yet sustain it as long 

 as she keeps her eyes fixed upon it, but no 

 longer, the muscles ceasing to contract, and 

 the limb dropping powerless, the moment that 

 the eyes are withdrawn from it. There are two 

 groups of muscular actions, however, which, 

 although as voluntary in their character as 

 the foregoing, are yet habitually guided by 

 other sensations than those derived from the 

 muscles themselves. These are, the move- 

 ments of the eyeball, and those of the vocal 

 apparatus. The former are directed (as Dr. 

 Alison has well shown *) by the visual sense, 

 by winch the action of the muscles is guided 

 and controlled in the same manner as that of 

 other muscles is directed by their own " mus- 

 cular sense ;" and hence it happens that, when 

 we close our eyes, we cannot move them in 

 any required direction, without an effort that 

 strongly calls forth the muscular sense, by 

 which the action is then guided. In persons 

 who have become blind after having once 

 enjoyed sight, an association is formed by 

 habit between the muscular sense and the con- 

 tractile action, that enables the former to 

 serve as the guide after the loss of the visual 

 sense ; but in those who are born perfectly 

 blind, or who have become so in early infancy, 

 this association is never formed, and the eyes 

 of such persons exhibit a continued indefinite 

 movement, and cannot by any amount of effort 

 be steadily fixed in one spot, or be turned in 

 any definite direction. A very small amount 

 of the visual sense, however, such as serves 

 merely to indicate the direction of light, is 

 sufficient for the government of the move- 

 ments of the eye-ball. 



In the production of vocal sounds, again, 

 that nice adjustment of the muscles of the 

 larynx, which is requisite to give forth deter- 

 minate tones, is ordinarily directed by the 

 auditory sense; being learned in the first 

 instance under the guidance of the sounds 

 actually produced ; but being subsequently 

 effected voluntarily, in accordance with the 

 mental conception (a sort of inward sensa- 

 tion) of the tone to be uttered, which concep- 

 tion cannot be formed, unless the sense of 

 hearing has previously brought similar tones 

 to the mind. Hence it is that persons who 

 are born deaf, are also dumb. They may 

 have no malformation of the organs of speech ; 

 but they are incapable of uttering distinct 

 vocal sounds or musical tones, because they 

 have not the guiding conception, or recalled 

 sensation, of the nature of these. By long 

 training, however, and by imitative efforts 

 directed by the muscular sense of the larynx 

 itself, some persons thus circumstanced have 

 acquired the power of speech ; but the want 



* Anatomical and Physiological Inferences from 

 the Study of the Nerves of the Orbit, in Trans, of 

 * Soc. Edinb., vol. xv. 



of a sufficiently definite control over the vocal 

 muscles is always very evident in their use of 

 the organ. It is very rarely that a person 

 who has once enjoyed the sense of hearing, 

 afterwards becomes so completely deaf, as to 

 lose all auditory control over his vocal organs. 

 An example of this kind, however, has been 

 made known to the public by a well known 

 author, as having occurred in himself; and 

 the record of his experiences * contains many 

 points of much interest. The deafness was 

 the result of an accident occurring in child- 

 hood, 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 

 resulted 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 in- 

 disposition to their employment; and thus, 

 for some years, the voice was very little ex- 

 ercised. Circumstances afterwards forced it, 

 however, into constant employment; and great 

 improvement has subsequently taken place in 

 the power of vocalisation, evidently by atten- 

 tion 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, are still pronounced (such of them, 

 at least, as are kept in employment) as they 

 were in childhood ; the muscular movements 

 concerned in their articulation being still 

 guided by the original auditory conception, in 

 spite of the knowledge derived from the in- 

 formation of others, that their pronunciation 

 is erroneous. On the other hand, all the 

 words subsequently learned are pronounced 

 according to their spelling ; the acquired as- 

 sociations between the muscular sensations 

 and the written signs being in this case the 

 obvious guide. 



The perception of "effort" which we 

 derive through the impressions made on the 

 muscular sense, is one which, as we shall 

 presently see, is of immense value, in com- 

 bination with simple tactile sensation, in 

 informing us of the sensible properties of 

 external objects. In its simplest exercise, 

 however, it enables us to appreciate the 

 degree of muscular force which is being 

 exerted ; and excites in our minds our most 

 definite idea of power. It is true that we 

 might, by the exercise of our other senses, 

 have arrived at the conception of a tendency 

 in bodies to attract one another, or to com- 

 municate motion one to another ; but the 

 notion of the force with which they do so is 

 entirely founded, directly or indirectly, upon 



* See the Lost Senses," by Dr. Kitto ; vol. i. 

 chapters 2 and 3. 



4F 3 



