882 OF SENSATION, AND THE ORGANS OF THE SENSES. 



diameter of the pupil. The fourth and sixth pairs, moreover, have not appeared 

 to the authors to possess any influence over the movements of the iris. If the 

 cervical sympathetic be galvanized without waiting for the gradual departure 

 of the constriction produced by the section of the fifth pair, it is found to be 

 powerless to overcome this constriction. If, moreover, the fifth pair be exposed 

 and its trunk be divided progressively from the centre towards the eye, it is 

 found that so soon as the section is carried in front of the anterior portion of 

 the Gasserian ganglion, the power of the sympathetic over the pupil is entirely 

 lost. Hence it seems evident that the sympathetic fibres which have this func- 

 tion pass through the Grasserian ganglion; and by other experiments it may be 

 shown that they form part of the ophthalmic division of the fifth pair. ED.] 1 

 883. The sense of Vision depends, in the first place, on the transference to 

 our minds of the picture which is formed upon the retina; this picture puts us in 

 possession of the outlines, lights and shades, colors, and relative positions, of 

 the objects before us; and all the ideas respecting the real forms, distances, 

 &c., of bodies, which we found upon these data, must be considered in the light 

 of perceptions, either instinctive or acquired. Many of these are derived 

 through the combination, in our minds, of the Visual sensations, with those 

 derived from the sense of Touch. Thus, to take a most simple illustration, the 

 idea of smoothness is one essentially tactile ; and yet it constantly occurs to us, 

 on looking at a surface which reflects light in a particular manner. But, if it 

 were not for the association, which experience leads us to form, of the connec- 

 tion between polish as seen by the eye, and smoothness as felt by the touch, we 

 should not be able to determine, as we now can do, the existence of both these 

 qualities, from an impression communicated to us through either sense singly. 

 The general fact that, in Man, the greater part of those notions of the external 

 world, by which his actions in the adult state are guided, are acquired by the 

 gradual association of the perceptions derived through the Sight and through 

 the Touch, is substantiated by amply sufficient evidence. This evidence is 

 chiefly derived from observations made upon persons born blind, to whom sight 

 has been communicated by an operation at a period of life which enabled them 

 to give an accurate description of their sensations. The case recorded by 

 Oheselden is one of the most interesting of these. The youth (about twelve 

 years of age), for some time after tolerably distinct vision had been obtained, 

 saw every thing flat as in a picture, simply receiving the consciousness of the 

 impression made upon his retina; and it was some time before he acquired the 

 power of judging, by his sight, of the real forms and distances of the objects 

 around him. An amusing anecdote recorded of him shows the complete want 

 x)f natural or intuitive connection which there is in Man between the ideas 

 formed through visual and through tactile sensations. He was well acquainted 

 with a Dog and a Cat by feeling ; but could not remember their respective 

 characters when he saw them. One day, when thus puzzled, he took up the 

 Cat in his arms, and felt her attentively, so as to associate the two sets of ideas; 

 and then, setting her down, said, "So, puss, I shall know you another time." 

 A similar instance has come under the Author's own knowledge; but the 

 subject of it was scarcely old enough to present phenomena so striking. One 

 curious circumstance was remarked of him, which fully confirms (if confirmation 

 were wanting) the view here given. For some time after his sight was tolera- 

 bly clear, the lad preferred finding his way through his father's house, to which 

 he had been quite accustomed when blind, by touch rather than by sight, the 

 use of the latter sense appearing to perplex rather than to assist him ; but when 

 learning a new locality, he employed his sight, and evidently perceived the 



1 "Brit, and For. Med.-Chir. Rev.," Jan. 1852, from "Gazette Medicale de Paris," 

 Nos. 41 and 44, 1851. 



