TOUCH. 



1163 



TOUCH. The sense through which we 

 take cognisance of the palpable properties of 

 bodies. The term is used, however, in two 

 meanings, between which it is requisite to 

 maintain a due discrimination. In its ex- 

 tended acceptation, it implies our conscious- 

 ness of all those sensory impressions, which 

 are neither olfactive, visual, auditory, nor 

 gustative ; and it is therefore designated as 

 the general sense, in contradistinction to 

 those, which are considered as special senses. 

 In its most limited application, on the other 

 hand, it is used to designate that modification 

 of the general sensibility, which is restricted 

 to the tegumeiitary surface, or to some special 

 portion of it, and which serves to excite 

 definite ideas in our minds respecting the 

 form, size, number, configuration, weight, tem- 

 perature, hardness, softness, &c,, of objects 

 brought within its cognisance. The use of 

 the sense of Touch, in the acquirement of 

 these ideas, is, as we shall see hereafter, a 

 very complex process ; involving not merely 

 the discriminating employment of the proper 

 organs of touch, but also the assistance of 

 muscular action, and of the information de- 

 rived from it by the " muscular sense." 



General Sensibility. The most universal 

 of all the qualities or properties of matter 

 (that, in fact, upon which our notion of 

 it is founded) is resistance; and it is of 

 this quality that we find the power of cog- 

 nisance most extensively diffused through 

 the body, and most universally possessed by 

 all beings endowed with consciousness. It 

 would seem to require nothing else than the 

 presence of nerves connected (directly or 

 indirectly) with sensorial centres ; for there 

 does not appear to be a need of any special 

 organisation, surrounding the peripheral ex- 

 tremities of these nerves, in order that they 

 may receive and transmit impressions. Thus 

 any unusual pressure on a nerve in its course 

 is at once perceived by the mind, not, 

 however, as pressure, but as a disagreeable or 

 painful sensation, which gives no indication 

 of the mode in which it was excited. The 

 nerves of smell, sight, and hearing, are not 

 thus affected by mechanical irritation, no 

 manifestations of pain being exhibited when 

 they are pinched, torn, lacerated, &c. ; and 

 the general sensibility winch these organs of 

 sense possess is dependent upon other nerves. 

 The nerves of taste, however, exhibit the 

 same susceptibility to tactile impressions, as 

 do those of touch ; and hence we have an 

 additional proof of the very close affinity of 

 these two senses (See TASTE). 



The only condition requisite for the ex- 

 ercise of " general sensibility," beyond the 

 integrity of the nervous apparatus, is the 

 adequate supply of oxygenated blood. Wher- 

 ever sensory nerves exist, we find them ac- 

 companied by blood-vessels ; and no non- 

 vascular tissue possesses in itself the least 

 degree of sensibility. Thus, in the epidermis, 

 hair, nails, cartilage, and tooth-substance, nei- 

 ther nerves nor blood-vessels exist, and we 

 find these tissues completely insensible. In 



tendons, ligaments, fibrous membranes, ami 

 in other parts whose function is purely me- 

 chanical, we find very little vascularity, and 

 extremely little sensitiveness to ordinary im- 

 pressions ; it is remarkable, however, that 

 although the tissues, whose function it is to re- 

 sist tension, are scarcely impressible by cutting, 

 burning, &c., they cannot be unduly stretched 

 without considerable pain. So, also, the serous 

 and synovial membranes are not in the least 

 susceptible of ordinary tactile impressions in 

 their healthy state ; but they become acutely- 

 sensitive when inflamed. It does not at all 

 follow, however, that the sensibility of a part 

 should increase with its vascularity ; for we 

 find that some of the most vascular organs in 

 the body are the least sensitive, the supply of 

 blood which they receive having some pur- 

 pose entirely different. Thus the sensibility 

 of the muscles is by no means proportionate 

 to the large amount of blood which they re- 

 ceive ; and even the substance of the brain 

 (like that of the nerves of special sensation) 

 is destitute of this property. So, again, the 

 mucous membranes lining the interior of the 

 several viscera, though supplied with blood 

 even more copiously than the skin, are very 

 far inferior to it in sensibility. The depend- 

 ence of this endowment, however, wherever 

 it exists, upon the continued circulation of 

 the blood, is at once made apparent by the 

 results of its suspension ; thus, when the 

 main artery of a limb is tied, there is a dimi- 

 nution of the sensibility both of its surface 

 and of its substance, which is so exactly 

 proportioned to the degree in which the sup- 

 ply of blood is diminished, and the reco- 

 very from which takes place so precisely in 

 accordance with the establishment of the col- 

 lateral circulation, that we cannot doubt that, 

 if the supply of blood were completely cut 

 off', sensibility would be entirely suspended. 

 The numbness produced by cold, in like 

 manner, is partly due to the stagnation which 

 it occasions in the capillary circulation in the 

 skin ; though it is doubtless in part attributable 

 to the immediate depressing influence of the 

 cold upon the vital endowments of the ner- 

 vous apparatus itself. 



The general sensibility of the body may be 

 called into activity by impressions received 

 from objects external to it, or by causes ori- 

 ginating in itself ; and the consequent sensa- 

 tions are sometimes distinguished as " ex- 

 ternal" and "internal." These designations 

 are by no means logically correct ; for all 

 sensations must originate in causes external 

 to the recipient mind; whilst, on the other 

 hand, in order that any sensation may be felt, 

 a certain condition of the corporeal organism 

 must first be produced ; and this condition 

 may be precisely the same, whether it be 

 immediately dependent upon changes ori- 

 ginating in the body itself, or upon changes 

 impressed upon it from some agency external 

 to it. Still, however, the terms " external " 

 and " internal " sensations are sufficiently con- 

 venient, and sufficiently free from the pro- 

 bability of misconception, to justify the phy- 



