128 SPECIAL HISTOLOGY. 



measurements of the sensitive roots of the spinal nerves (vide 

 1 Mic. Anat./ p. 433). With the number of the nerves, is con- 

 nected 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 : I , how it is that we do not distinguish with the 

 same clearness and exactness, 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 circum- 

 stances, appear double, under others single (Weber's experi- 

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

 by the mode of distribution of the peripheral nerves, but 

 depends very probably upon their central relations. It seems 

 to me to be simplest to assume, that every peripheral end of a 

 nerve is capable, when irritated, of producing a conscious 

 sensation, but that, on account of the small number 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 consciousness by more numerous 

 intermediate fibres than those of other localities, and at the 

 ends of these fibres, also, we must suppose a sort of interlace- 

 ment to take place. Upon this hypothesis, the former of the 

 two points might be explained. A local irritation is, indeed, 

 felt locally; but, according 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 

 I"' — V", while, in others, they may extend to l" — 1*" and 

 more. 



E. H. W T eber has endeavoured to demonstrate, in his last 

 able Treatise upon the sense of touch, that it is only the ter- 

 mination 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 suppo- 

 sition, that tactile organs as yet unknown may exist in the 



