136 SPECIAL HISTOLOGY. 



periment teaches that though all points of the skin may not feel with 

 the same delicacy, they are all nevertheless sensitive. I hoped to be 

 able to submit Wagner's doctrine of the absence of nerves in many 

 papillae to experimental proof, by examining the sensitiveness of various 

 parts of the body with the finest possible English sewing needle. At 

 first I really thought that I had found some places which were quite in- 

 sensible, whilst in others the slightest touch produced sensation ; but on 

 carrying the investigation further, it appeared that the very same place 

 was often sometimes sensible, sometimes not ; so that, finally, I came 

 to the conclusion that the very smallest portions of the skin are sensitive. 

 But since even in the palm of the hand the papillae containing nerves 

 are widely dispersed, and in other places occur but rarely, or even not 

 at all, it only remains either to assume the existence of non-medullated 

 nerve-fibres in all the papillae, 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 state- 

 ment may be made. 



The excitement of the terminations of the nerves in the outermost 

 parts of the cutis and the papillae 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 mediation of the epidermis, one of the func- 

 tions 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 viva- 

 city of the sense of touch are not everywhere 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 ab- 

 domen. 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. Sim- 

 ple inspection teaches that the nerves upon the palm of the hand and 



