1176 



TOUCH. 



quire the effort of a contrary set of muscles for 

 the maintenance of the erect position. 



Mental Phenomena connected with the Sense. 

 The interpretation which the mind puts 

 upon the impressions made by external ob- 

 jects upon the tactile organs, is partly the re- 

 sult of intuition, partly of experience. Thus 

 we intuitively refer an impression made upon 

 any part of a sensory nerve in its course, to 

 the peripheral extremities of that nerve, or 

 (as in cases of amputation) to the part from 

 which they should normally arise. So, again, 

 if a part of the body be removed from its 

 usual position and connections (as in the 

 Taliacotian and various other operations of 

 plastic surgery), impressions made upon it 

 continue to be referred to its original seat, so 

 long as it retains any nervous connection with 

 it, and until new connections have been 

 formed with the nerves of the part to which it 

 has been transferred. So, again, when our 

 members are in an unaccustomed position, 

 we still, unless our attention be directed to 

 the fact, interpret impressions made upon 

 them as if they were in their ordinary relation 

 to each other, and may thus be altogether 

 misled : as in the experiment mentioned by 

 Aristotle, of rolling a pea or other globular 

 body between two fingers of one hand, which 

 are crossed instead of lying parallel, so that 

 the surfaces that are usually most distant 

 are brought into proximity with each other ; 

 the sensation then received is that of a dis- 

 tinct convex body opposed to each of these 

 surfaces, so that the single body seems to be 

 double; whereas, if the pea were rolled be- 

 tween the two surfaces which are usually and 

 normally approximated, it is felt but as a single 

 globe. This intuitive reference is obviously 

 analogous to that by which we judge of the 

 relative situations of visual objects, from the 

 direction in which their rays impinge upon the 

 retina, or from the muscular sensations re- 

 ceived from the muscles of the orbit. 



In a large proportion of other cases, how- 

 ever, our interpretation of our tactile sensa- 

 tions, especially of all those which relate to 

 the configuration, density, &c. of external ob- 

 jects, is based on experience ; and those who 

 watch the eagerness with which the infant 

 grasps and examines by its touch every attrac- 

 tive object within its reach, are at no loss to 

 perceive how the experience thus early inter- 

 woven (as it were) \vith the mind, in combin- 

 ation with that derived through the visual 

 sense, comes to supply the place of the con- 

 genital intuitions of the lower animals, and 

 to cause the tactile and visual perceptions to be 

 henceforth so indelibly associated, that each 

 is continually suggesting the other. Thus, 

 the notion of projection, which we derive 

 through the sight, comes to be associated 

 with that of solidity, which we receive through 

 the touch ; and the visual notion of polish is 

 so closely connected with the tactile notion 

 of smoothness, that the one almost necessarily 

 suggests the other. There is abundant evi- 

 dence, however, that there is no necessary or 

 intuitive connection between the ideas which 



we derive through these two senses respec- 

 tively ; but that this connection is acquired 

 by the consentaneous exercise of them. Thus, 

 from observations made upon persons born 

 blind, when visual power has been first ob- 

 tained, it is certain that the notions of form 

 previously acquired by the touch do not aid 

 in the visual discrimination or recognition of 

 objects : so that, for example, if any such 

 person had previously learned to distinguish 

 a sphere, a cube, and a pyramid, by the touch, 

 he would not be able to say which was which 

 by looking at them, until he had learned by 

 experience to associate the two classes of per- 

 ceptions : and, conversely, we cannot but be- 

 lieve that the same result would occur, if a 

 person whose notions of the external world 

 were derived from the sight alone, were sud- 

 denly and for the first time to become en- 

 dowed with the sense of touch. 



It is, in fact, no less clear in regard to the 

 sense of touch than it is in regard to vision, 

 that it is not the sentient organ (as we are 

 accustomed to term it), but the mind, which 

 really perceives ; and that all the notions 

 which we derive through this sense with re- 

 spect to external objects, whether they be of 

 the most general kind or of a more particular 

 nature, are altogether distinct from the sensa- 

 tions themselves. It has been well remarked 

 by Professor Alison, that " one decisive proof 

 of this being the true representation of this 

 part of our mental constitution is obtained by 

 attending to the idea of extension or space, 

 which is undoubtedly formed during the exer- 

 cise of the sense of touch, but which is no 

 sooner formed than it ' swells in the human 

 mind to infinity,' to which, certainly, no 

 human sensation can bear any resemblance."* 

 So, again, the elementary notion of an ex- 

 ternal universe as something distinct from the 

 individual self, is altogether distinct from the 

 sensations which excites it. All that the 

 mind is conscious of, is a change in the condi- 

 tion of the corporeal organism ; and the re- 

 ference of the source of this change to some 

 external agency is a mental process in which 

 the action of the purely sensorial apparatus 

 has no concern. 



It has been thought by some that the notion 

 of an external world depends more upon the 

 sensations received through the touch, than 

 upon those of any other kind. But there 

 does not seem to the author to be any reason 

 for considering that simply tactile impressions 

 are more necessarily or intuitively recognised 

 as proceeding from an external source than 

 are the visual, olfactive, auditory, or gustative. 

 But, as already shown, it is from the muscular 

 sense that we derive the idea of force, involv- 

 ing resistance to our own voluntary efforts ; 

 and it would seem to the writer to be on this 

 notion that our belief in the existence of an 

 universe external to ourselves most securely 

 rests. 



The active co-operation of the mind is re- 

 quired, not only for the formation of the 



* Outlines of Physiology, 3rd ed. p. 290. 



