SENSE OP TOUCH. 157 



directing the attention, the impression may be rendered more 

 vivid. 



4. /The sense of touch is the general feeling or sensibility 

 produced by the skin, and which instructs us regarding the 

 general qualities of bodies.) It resides also to some extent 

 in mucous membranes, as in the mouth, throat, &c., although 

 in a very imperfect degree. For example, we cannot feel 

 the pulse by placing the tongue over it on the wrist, as any 

 one can ascertain by trying the experiment. fThe sense of 

 touch is distinguished by some writers from that of feeling, 

 but they are only modifications of the same sense. 



5. I have already given some account of the structure of 

 the skin, and stated that it is Divided into four layers, viz., 

 the (cuticle, mucous web, papillary body, and true skin } and 

 thatT^he cuticle is the thin, transparent pellicle^or membrane, 

 whichfforms the external incrustment of the body, protecting 

 those papillae, in which reside the sense of touch.) As no 

 blood-vessels or nerves have been traced in it, it is supposed 

 to be an unorganized texture, or an albuminous secretion, 

 poured out by the subjacent vessels, and hardened by the in- 

 fluence of the air. This accounts for its rapid formation, 

 when destroyed by a blister, burn, &c. When a part of the 

 body is exposed to irritation, the vessels which pour out the 

 lymph, from which the cuticle is derived, have their action 

 increased, and the cuticle either becomes thickened, as in 

 the palms of the hand and soles of the feet, or the effusion is 

 so abundant as to cause a separation between it and the true 

 skin, causing blisters. 



6. Now, it is a general law, that pressure promotes ab- 

 sorption ; and we see this exemplified daily in cases of 

 tumours, abscesses, bandaging for dropsical effusions, &c. 

 Had this tissue been subjected to this general law^the fric- 

 tion and pressure to which the cuticle of the hands is ex- 

 posed in manual labour, and of the feet in walking, would, 

 in a short time, have entirely deprived them of protection, 

 instead of rendering their covering more dense and thicker, 



14 



