I. Maclaren Thompson 559 



extending from the electrode, along the nerve stimulated and its central path- 

 ways, to the sensorium (but not upon anything distal to the electrode, even in 



an unblocked nerve). 



Conclusion 



Notwithstanding the slight inconsistencies common in work of this kind, these 

 various experiments, taken as a whole, show that the threshold for deep-pres- 

 sure in muscles, etc., supplied by the deep branch of the ulnar nerve may be 

 elevated by suitable electrical stimulation of any other nerve in the forearm 

 and hand. This proves that the phenomenon is not one of peripheral block. 

 (If it were, only stimulation of the deep branch of the ulnar nerve could raise 

 the threshold in structures supplied by it.) Nor does it depend upon retrograde 

 stimulation of end-organs. (If it did, elevation of pressure threshold in muscles 

 supplied by one nerve could not be produced by stimulating another cutayie- 

 ous nerve.) It may be concluded that this type of masking depends upon a 

 mechanism within the central nervous system. This is supported by the in- 

 variable association of masking with a tingling or throbbing sensation. 



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