jo So THE SENSES 



bility to touch and temperature, showing a central area of absolute 

 anaesthesia surrounded by a zone of partial loss, which is slight 

 towards the outer boundary, but increases as we pass inwards 



(Fig. 446). 



After section of a nerve function is recovered only as a result of 

 regeneration. This is true of all the sensory functions of the skin 

 and of the pilo-motor and sudo-motor functions. Vaso-motor tone 

 in the affected area is restored much sooner than the other functions. 

 This rapid recovery probably depends upon a local compensatory 

 mechanism, and not upon regeneration of the vaso-motor fibres. 

 Recovery of all the functions dependent upon regeneration begins 

 about the same time, and this recovery progresses over the area at 

 about the same rate for all, although the rate at which they progress 

 towards normal acuity is different. 



Sensibility to touch probably appears a little earlier than sensi- 

 bility to cold and pain. Yet the recovery of touch does not progress 

 so fast, and for a while a given zone of the recovering area remains 

 hyposesthetic (less sensitive than normal) to touch, while to cold 

 and pain it soon becomes even hypersensitive. The most remark- 

 able peculiarities of a recovering area are : (i) This qualitative 

 change, in virtue of which cold, pain, and the pain element of heat 

 are intensified, while touch is little altered, although more difficult 

 to elicit ; (2) the reference of sensations, not to the point stimulated, 

 but to distant parts of the area. 



'When a spot which has developed this peripheral reference is 

 touched, one of two possibilities may occur: either the touch is 

 felt locally, and is referred as well, or nothing is felt locally, and 

 the touch is felt in the area of peripheral reference. The region 

 in which the referred touch is felt is always at the edge of the most 

 peripheral part of the anaesthesia/ perhaps more than a foot away 

 from the spot actually touched. The peripheral reference of cold 

 is even more striking, particularly in the remarkable intensity of 

 the referred sensation. 



Peripheral reference occurs also with pain. ' The referred pain 

 shows three well-marked qualities: it is, proportionately to the 

 stimulus, very intense ; it does not reproduce a normal sensation 

 with the exactitude found hi the case of touch or cold, but has a 

 special quality of strangeness and unpleasantness, such as no pin- 

 prick on normal skin can give; finally, it produces an almost irre- 

 sistible desire on the part of the subject to rub or scratch the region 

 in which it is felt.' As recovery proceeds the local sensory response 

 becomes more distinct, and the abnormal quality of both local and 

 referred sensations fades. But ' while peripheral reference is the 

 earliest phenomenon of recovery, it persists until recovery is so far 

 advanced that hypoaesthesia is scarcely detectable by any quanti- 

 tative methods.' 



