Release of Function in the Nervous System. 



199 



we find that the first sorting of afferent impulses within the spinal cord is 

 concerned mainly with their redistribution according to quality. Those 

 capable of exciting pain are gathered together, whatever their peripheral 

 origin, and all those which can evoke sensations of heat or of cold are 

 combined in two specific groups. 



After the multitudinous impulses jDroduced by the impact of external 

 and internal forces on the organism have carried out their reflex and 

 co-ordinating functions, the remainder may pass on to excite sensations. 

 These form an essential element in conscious acts, and here the rigidity of 

 response, so characteristic of reflex activity, would be disastrous. The 

 limited freedom of the lower levels must be expanded, so that the physio- 

 logical reaction may become less inevitable and more elastic. 



Moreover, the sensations to which these impulses can give rise are 

 frequently incompatible ; a temperature of about 45° C. stimulates at one 

 and the same time organs capable of evoking pleasant heat, cold, and pain. 

 These sensory and affective states cannot co-exist in consciousness ; the 

 struggle between the diverse groups of afferent impulses takes place, 

 therefore, on the physiological level, and the victor alone appears as a 

 sensation. 



The simplest sensory act is the result, not only of prolonged qualitative 

 integration, but of a constant struggle for physiological dominance. Under 

 normal conditions the result may be inevitable ; but there are many cases 

 especially within the visceral field, where no general rule can be laid down, 

 and the response depends on the patient's idiosyncracy or general resistance. 

 Moreover, his usual reaction may become changed in consequence of some 

 functional alteration in the activity of the central nervous system ; impulses 

 may then excite sensation, which normally would have remained outside 

 consciousness. 



The following observation, made on my hand in the later stages of regenera- 

 tion, reveals the struggle for dominance amongst the various afferent impulses 

 excited by thermal stimulation. The dorsal portion of my thumb had so far 

 recovered that contact with a large vessel containing water at 40° C, produced 

 a pleasant well localised sensation of warmth. But, at the same time, the 

 skin in the neighbourhood of the index knuckle was in a pure condition of 

 primitive sensibility, and a cold tube applied to this area evoked a diffuse and 

 vivid outburst of cold referred to the back of the thumb. It was, therefore, 

 possible to stimulate the skin of the thumb with heat, and simultaneously to 

 evoke a sensation of cold referred to the same area. As soon as this was 

 brought about all sensations of heat and cold ceased in the thumb and were 

 replaced by discomfort and pain. When, however, the cold tube was removed 



