Release of Function in the Nervous System. 



191 



activity by 20° C, a stimulus at the same temperature, sufficiently extensive 

 to cover many cold spots,, will seem to be colder, although in reality its 

 intensity is the same. Thus, whenever sensation depends solely on the 

 response of this class of end-organs, the extent of the stimulus is of greater 

 importance than its intensity. 



A peculiarity of this reaction, from any part of the skin innervated by 

 this punctate system only, is the diffuseness and wide radiation of the 

 sensation evoked. When a hair-clad part, such as the back of the hand, 

 is stroked with cotton-wool, an intense " tingling " and " itching " is produced 

 over widely remote parts of the affected area. This disappears when the 

 skin is shaved, and is due to movement of the shafts of the hairs ; it is 

 not a function of the skin as a whole. In the same way, each effective hot, 

 cold or painful stimulus produces its specific sensation, which is referred 

 to the same remote parts of the affected area, irrespective of any difference 

 in quality ([9], p. 302). 



Thus an area, obviously defective in sensibility, is found to respond with 

 extraordinary vividness and with a widespread massive sensory reaction. 

 These manifestations grow steadily stronger throughout the first stage of 

 recovery, with the gradual return of sensibility to pain and the increasing 

 number of heat- and cold-spots. 



Throughout this period the more discriminative aspects of sensation have 

 been absent or very defective. But as soon as they begin to return, the 

 mode of reaction changes. The diffused sensations give place to a more 

 strictly localised response ; radiation no longer occurs into remote parts 

 of the affected area. At the same time, the power returns of distinguishing 

 two compass-points, applied simultaneously. This is essentially an ability 

 to recognise objects in two dimensional space, and it is this discriminative 

 power which checks and controls the diffuse character of the more primitive 

 method of response. The impulsive reaction of the heat- and cold-spots 

 gives place to one graduated more closely according to the intensity of the 

 stimulus, as the affected part becomes sensitive to temperatures which lie 

 in the middle of the scale (27° to 38° C). 



Another remarkable change, due to the restoration of the more dis- 

 criminative aspects of sensibility, is shown in the return of adaptation 

 to different temperatures. Under normal conditions, if the hand has been 

 exposed for some time to warmth, a stimulus at 29° C. may seem to be 

 " cool," whilst, conversely, if it has been adapted to cold, the same object 

 may appear to be " warm." So long as the skin is actively innervated 

 solely by the punctate sensory mechanism, no such adaptation is possible 

 within normal limits, and any effective thermal stimulus appears to be hot 



