CHAP. vi.J ON CUTANEOUS SENSATIONS. 303 



case the finger has been gradually carried out of the plane, where- 

 upon we judge the surface to be curved, and that in the third case 

 the movement of the finger has been irregular, whereupon we 

 judge that the surface is irregular ; and so on. In each case we 

 estimate the movement by the muscular sense,- and thus by a 

 combination of muscular sense and of touch we form a judgment 

 of the conformation of external bodies. In the same way, and 

 indeed as part of the same process, by a combination of the mus- 

 cular sense and of touch we estimate the size of external objects. 

 By a like double act we estimate the position in space in relation 

 to our body of such objects as are within our reach, such as can be 

 touched either directly by one of our limbs or indirectly by help 

 of a stick or otherwise. So closely bound together are the muscu- 

 lar sense and the sense of touch proper, that in common language 

 we speak of learning this or that by touch, when we really 

 employ both senses. 



896. No less close are the ties between sight and touch ; 

 indeed a very large part of our psychical life is built up on the 

 association of visual and tactile sensations. There is no part of 

 the external world, including our own bodies, which we can explore 

 by touch, which we cannot, either directly or by optical aids such 

 as mirrors, also explore by vision ; and our conceptions of the 

 nature of all such things is the outcome of a combination of the 

 two senses, or rather bearing in mind what has just been said, of 

 the three senses, sight, touch and the muscular sense. It is rela- 

 tively easy to recognize blindfold by touch alone, the characters of 

 objects with which we are already previously familiar by help of 

 vision ; but it is very difficult to form by touch alone an accurate 

 judgment of the form and size of objects which we have never 

 seen. Were we limited to sight alone, we should form one set of 

 conceptions of the world, were we limited to touch we should form 

 another ; and the two sets would be different. 



In the conceptions which we form in actual life the two are 

 combined. The congenitally blind are limited to one set only; 

 and, when, as has happened in cases of congenital cataract, those 

 who have been blind from birth are restored to vision after they 

 have grown up and have accumulated a store of tactile con- 

 ceptions, they fail at first to connect their new visual sensations 

 with their old tactile experience. The stories of the first experi- 

 ences in vision of such persons, as that for instance of the man 

 who had to feel a cat in order to connect the visual image with 

 his previous tactile image, and having carefully felt it all over 

 said " Now, Puss ! I shall know you again," illustrate the close 

 dependence on each other of visual and tactile normal percep- 

 tions. This is also indicated by the zeal with which in former 

 days the question was discussed whether a man who had been 

 born blind and restored to sight in adult life, could recognize at 

 first sight and by sight alone a cube, a square, and a sphere. It is 



