OF THE SKIN. 127 



cither to assume the existence of non- medullated nerve-fibres 

 in all the papillse, or to have recourse to the nervous plexus at 

 the base of the papillae. I should unhesitatingly prefer the 

 latter explanation, were it not : (1 ) that these plexuses are in 

 many places so very scanty, and (2) that the slightest touch of 

 the epidermis produces sensation ; for the present, therefore, I 

 believe this must remain an open question. 



If we are not in a condition to understand how it is that 

 every point of the skin is sensitive, still less are we competent 

 to explain the different kinds of sensations. In this respect 

 the following very general statement may be made. 



The excitement of the terminations of the nerves in the 

 outermost parts of the cutis and the papillse is either direct or 

 indirect. The former as it is produced, for example, when the 

 cutis is laid bare, by penetrating instruments and by fluids, is 

 much more intense than that which takes place through the me- 

 diation of the epidermis, one of the functions of the latter being 

 to act as a defence against too violent impressions, and to 

 blunt them according to its greater or less thickness. It can 

 now be partly explained on anatomical grounds, why the 

 delicacy and vivacity of the sense of touch are not every- 

 where equal, why they are less upon the hairy scalp, the back, 

 the two upper divisions of the extremities, than on the face, 

 on the genitalia, the hand and foot, the chest and abdomen. 

 In the first place, where the tactile sense is delicate, the epi- 

 dermis is in itself thin, as upon the eyelids and face, or has, at 

 least, a thin horny layer, as upon the penis and clitoris, 

 whilst upon the back and extremities it is considerably 

 thicker. Yet this circumstance is not a sufficient explanation, 

 for parts with a thicker epidermis, as the palm of the hand 

 and the sole of the foot are delicately sensitive, more so, in 

 fact, than others with a thinner covering, as the back of the 

 hand and foot. Another condition must here obviously come 

 into play, and it is, I think, that the skin is not equally well 

 provided with nerves in all its parts. Simple inspection teaches 

 that the nerves upon the palm of the hand and the sole of the 

 foot are more numerous than upon the back of the hand and 

 foot ; upon the glans penis and clitoridis, the nipple, the face, 

 they are more abundant than upon the abdomen, back, and 

 thigh, &c. &c. ; and this is to some extent confirmed by my 



