i CUTANEOUS SENSIBILITY 43 



Adult. Boy. 



Lower occipital region ... . . 27-1 22-6 



Doreum of hand .... . . 31-6 22-6 



Chin . . . 33-8 22-6 



. 33-8 22-6 



. 36-1 31-6 



. 40-6 33-8 



. 40-6 36-1 



. 40-6 36-1 



. 45-1 33-8 



Vertex of head 



Knee-joint 



Sacral and gluteal regions 



Forearm and leg 



Dorsum of foot near toes 



Sternum 



Neck, high up 54-1 36-1 



Dorsal spine, lower thoracic and lumbar region . . . ... 54-1 



Middle of neck 67-7 



Middle of arm, thigh, back 67-7 40-6 



Weber gave the name of tactile circle to the area within which 

 the two points of the aesthesiometer are appreciated as a single 

 point. If in any cutaneous area the localisation is equally developed 

 in all directions, the circles are round, i.e. they approximate to 

 the figure of a true geometrical circle; but this is very seldom 

 the case. More often, particularly in the extremities, they are 

 oval, because tactile discrimination is, as we have seen, more 

 developed in the transverse than in the longitudinal direction. 

 For this reason Hermann prefers the term tactile fields to tactile 

 circles. 



These tactile circles or fields have no fixed anatomical limits, 

 and do not correspond to the peripheral distribution of a single 

 nerve -fibre. If they did there would be a sudden transition 

 from a single perception (when the two points were applied 

 within one circle) to a double one (when the equidistant points 

 were applied to two adjacent circles), which is not the case, 

 since each point of the skin may bej taken as the centre of a 

 circle. As, moreover, discriminative sensibility differs enormously 

 in different regions of the skin, as shown by the above table, 

 this assumption is obviously irreconcilable with such a varying 

 peripheral distribution of the sensory cutaneous fibres in the 

 different parts. Weber accordingly assumed that each tactile 

 circle contains many nerve -endings, and that for the recognition 

 of the two contacts it is necessary that there should be between 

 the two excited nerve-endings a certain number of unexcited 

 end-organs, which vary in different regions according to their 

 congenital arrangement. This theory is obviously less an explana- 

 tion than a simple statement of fact. It does not explain how 

 the tactile fields can be diminished by practice. 



From the psychological point of view Lotze supposed that 

 each nerve- fibre distributed to the skin or adjacent mucous 

 membranes is provided in the brain with a local sign of recognition 

 of the place to which it is distributed in the periphery. In 

 developing this idea Wundt concluded that on stimulation each 

 cutaneous area transmits to the brain not only the impression of 



