FUNCTIONS OP THE SENSORY GANGLIA. 723 



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 contractile 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 move- 

 ment, 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 movements of the eyeball. In the production of vocal 

 sounds, again, that nice adjustment of the muscles of the larynx, which is re- 

 quisite to give forth determinate tones, is ordinarily directed by the auditory 

 sense : being learned in the first instance under the guidance of the sounds actu- 

 ally produced; but being subsequently effected voluntarily, in accordance with 

 the mental conception (a sort of inward sensation) of the tone to be uttered, 

 which conception cannot be formed, unless the sense of hearing has previously 

 brought similar tones to the mind. Hence it is that persons who are born 

 deafj are also dutnb. 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 muscular sensa- 

 tions in the larynx itself, some persons thus circumstanced have acquired the 

 power of speech : but the want 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 com- 

 pletely 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 1 contains many 

 points of much interest. The deafness was the 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 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 

 indisposition to their employment ; and thus, for some years, the voice was very 

 little exercised. Circumstances afterwards forced it, however, into constant 

 employment; 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, are still pronounced 

 (such of them, at least, as are kept in employment) as they had been in child- 

 hood; the muscular movements concerned in their articulation being still guided 

 by the original auditory conception, in spite of the knowledge derived from the 

 information of others, that such pronunciation is erroneous. On the other hand, 

 all the words subsequently learned are pronounced according to their spelling ; 

 the acquired associations between the muscular sensations and the written signs 

 being in this case the obvious guide. 



752. It is through the muscular sense, in combination with the visual and 

 tactile, that those movements are regulated which are concerned alike in ordi- 



1 See the " Lost Senses," by Dr. Kitto ; vol. i. chapters 2 and 3. 



