390 TACTILE SENSIBILITY OP THE SKIN. 



Sense of Touch. 



490. By the sense of Touch is usually understood that 

 modification of the common sensibility ( 487) of the body, of 

 which the surface of the skin is the especial seat. In some 

 animals, as in Man, nearly the whole exterior of the body is 

 endowed with it in no inconsiderable degree ; but in others, 

 as in the larger number of Mammals, most Birds and Eep- 

 tiles, and many Fishes, the greater part of the body is so 

 covered by hairs, scales, or bony plates, as to be nearly insen- 

 sible ; and the faculty is restricted to particular portions of 

 the surface, which often possess it in a very high degree. 

 The sensory impressions, by which we receive the sensation of 

 Touch, are made by the objects themselves upon the nerves 

 which are distributed to the Skin ; the general structure of 

 which has been already described ( 36 38). Of the papillce 

 which are thickly set upon many parts of its surface, some 

 contain looped tufts of blood-vessels without nerves ; and as 

 these are found to be largest where the Epidermis is thickest 

 (as, for example, in the pads on the under side of the Dog's 

 foot), it seems obvious that they minister, not to sensation, 

 but to the nutrition of that protective coating ( 492). But 

 in other papillae the blood-vessels are comparatively scanty, 

 their interior being chiefly occupied by little cushions of con- 

 densed areolar substance to which the sensory nerves proceed ; 

 and as their Epidermic coating is thin, and as the degree 

 of sensibility of any part of the skin bears a close correspond- 

 ence to the number of these papillae which are included 

 within a given area of its surface, it can scarcely be doubted 

 that they are the special instruments of the sense of Touch. 



491. The true skin, or Cutis ( 37), from which alone 

 leather is prepared, is thicker in most Mammals than in 

 Man ' } but the thickness of the skin does not by any means 

 involve (as is commonly supposed) deficient sensibility. Thus, 

 in the Spermaceti Whale it has been observed that the 

 sensory nerves, which are destined to be distributed on the 

 skin, pass through the blubber without giving off any con- 

 siderable branches, but spread out into a network of extreme 

 minuteness as soon as they arrive near the surface. It is 

 a fact well known to Whale-fishers, especially to those who 

 pursue this species, that these animals have the power of 



