CHAP, vi.] ON CUTANEOUS SBNSATIONa 



in another case the finger has been gradually carried out of 

 the plane, whereupon 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 mus- 

 cular 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 pro- 

 cess, by a combination of the muscular 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 muscular 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. 



664. 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 concep- 

 tions of the nature of all such things is the outcome of a com- 

 bination of the two senses, or rather bearing in mind what has 

 just been said, of the three senses, sight, touch, and the muscu- 

 lar sense. It is relatively easy to recognize blindfold, by touch 

 alone, the characters of objects with which we are already pre- 

 viously 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 tac- 

 tile conceptions, they fail at first to connect their new visual 

 sensations with their old tactile experience. The stories of the 

 first experiences in vision of such persons, as that for instamv 

 of the man who had to feel a cat in order to connect the visual 

 image with his previous tactile image, and having carefully tVlt 

 it all over said "Now, Puss! I shall know you again." illus- 

 trate the close dependence on each other of visual and tactile 

 normal perceptions. This is also indicated by the zeal with 

 which in former days the question was discussed whether a man 



