Release of Function in the Nervous System. 197 



complete and, when disintegration occurs, the separated spinal cord still 

 retains certain functions which in man have mostly been assumed by higher 

 centres. No flexor response is so free from postural characters as that which 

 can be obtained from the lower portion of the human spinal cord after 

 complete division. In the same way, the reactions of the optic thalamus in 

 man, freed from cortical control, are an almost perfect expression of the non- 

 discriminative aspects of sensation. ' 



2. Escape from Control. 



So far the phenomena I have described were due to disintegration of a 

 complex function, normally carried out by the co-ordinated activity of centres 

 at different levels of the nervous hierarchy. Before two such centres can 

 work harmoniously, their various activities niust be integrated, and during 

 this process some impulses are inhibited, whilst others are facilitated. Of two 

 antagonistic reflexes one becomes dominant, whilst the other is suppressed, 

 accoi'ding to circumstances, which are often more dependent on past events 

 than on the immediate character of the stimulus. The issue of a conflict 

 between opposing impulses is not inevitable ; it is always possible for an 

 unexpected or " abnormal " reaction to make its appearance, owing to some 

 change in functional balance (Sherrington [16], p. 135). 



The following experiment shows how completely one group of afferent 

 impulses may inhibit another under perfectly normal conditions. On care- 

 fully exploring the back of the hand two or more cold-spots can usually be 

 discovered in close proximity to one another. Stimulate any one of them 

 by means of a metal rod, with a blunt end of not more than 1 mm. in 

 diameter, heated to about 45° C. ; the sensation will be one of coldness, as if 

 the rod had been dipped in cold water. This is the familiar phenomenon of 

 " paradox cold." Take a flat-bottomed metal tube containing water at about 

 45° C, of such a size that it will cover several cold-spots together with the 

 skin around them. Lay this on the hand and you will experience a pure 

 sensation of heat ; and yet observation teaches us that this temperature is 

 capable of evoking a sensation of cold, if it is applied to each of the cold- 

 spots individually. Under normal conditions, however, the effect produced 

 by stimulating the cold-spots is dominated, before it can affect consciousness, 

 by the coincident impulses due to action of the same external physical agent 

 on the end-organs which respond to heat. 



The older investigators believed that an impulse, once started in specific 

 end-organs, travelled unchanged to the highest receptive centres, to evoke a 

 response corresponding in quality and degree to the sensory attributes of the 

 physical stimulus. Such a theory ignores the fact that 45° C. is an effective 



