OP THE SKIN. 137 



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 bj my measurement of the sensi- 

 tive roots of the spinal nerves (vide "Mic. Anat.," p. 433). With the 

 number of the nerves, is connected that of the actually demonstrable 

 dark-contoured nerves in the papillae and the superficial nervous plexus, 

 for nowhere is this more considerable than in the points of the fingers, 

 the lips, the tip of the tongue, and the glans penis. 



As to the local sensibility of the skin, it is the province of anatomy, 

 especially, to afford information, with regard to these two points : 1, 

 how it is that we do not distinguish with the same clearness and exact- 

 ness, in all parts of the body, the point at which a single irritation 

 is applied : and 2, why two stimuli operating at the same time, under 

 certain circumstances, appear double, under others single (Weber's 

 experiment). I think that Weber's experiment cannot be explained by 

 the mode of distribution of the peripheral nerves, but depends very pro- 

 bably upon their central relations. It seems to me to be simplest to as- 

 sume, that every peripheral end of a nerve is capable, when irritated, of 

 producing a conscious sensation, but that, on account of the small num- 

 ber of nervous fibres (in the cerebrum) which unite these with the seat of 

 consciousness, if many contiguous, or even more distant, cutaneous nerves 

 are excited, only a single conscious sensation results. In this case, the 

 nerves of acutely sensitive parts must be connected with the seat of con- 

 sciousness by more numerous intermediate fibres than those of other locali- 

 ties, and at the ends of these fibres, also, we must suppose a sort of inter- 

 lacement to take place. Upon this hypothesis, the former of the two points 

 might be explained. A local irritation is, indeed, felt locally ; but, accord- 

 ing as the nerves implicated are united with the brain by more or fewer 

 conductors in the spinal cord, are we able to assign, more or less exactly, 

 the precise spot ; so that, in some cases the limits of error will not exceed 

 J-l line, while in others, they may extend to 1 or 1J inch and more. 



E. H. Weber has endeavored to demonstrate, in his last able Treatise 

 upon the sense of touch, that it is only the termination of the nerves in 

 the skin, not the fibres in the nervous trunks, which are the mediators 

 of the sensations of pressure, warmth, and cold ; and he has expressed 

 a supposition, that tactile organs as yet unknown may exist in the skin. 

 R. Wagner believes that he has, in fact, found these organs in his so-called 

 corpuscula tacttis, and he supposes that, composed as they are, accord- 

 ing to him, of superimposed membranes, in the interspaces of which a 

 very minute quantity of fluid is lodged, like elastic cushions, or a bladder 

 filled with water, they are specially fitted to receive impressions from the 

 epidermis at the extremity which is directed towards it, and to transmit 

 them to the ends of the nerves which lie in and upon them. 



In my opinion, Weber's view of the greater sensibility of the termi- 



