I. Maclaren Thompson 557 



proximal to a procaine block, raised the pressure threshold in structures sup- 

 plied by the deep branch of the ulnar nerve. 



(5) The radial nerve being blocked, the median nerve was stimulated at the 

 wrist twenty times (three subjects): the deep-pressure threshold beneath the 

 anesthetized skin was unaltered once, and was significantly raised nineteen 

 times. 



(6) The radial nerve being blocked, the dorsal branch of the ulnar was 

 stimulated four times (one subject): each time the deep-pressure threshold 

 beneath the anesthetized skin was significantly raised. 



(7) The radial nerve being blocked, the medial cutaneous nerve of the fore- 

 arm was stimtdated twenty times (three subjects): the deep-pressure threshold 

 beneath the anesthetized skin was unchanged four times, but was significantly 

 raised sixteen times. 



Similar experiments were performed with the dorsal branch of the ulnar 

 nerve blocked. 



(8) The median was stimulated at the wrist twenty-five times (three sub- 

 jects): six times there was no change in the deep-pressure threshold beneath 

 the anesthetized skin, twice there was a fall in the threshold, and seventeen 

 times a significant rise. 



(9) The radial was stimulated eleven times (three subjects): four times there 

 was no change in the deep-pressme threshold, seven times there was a signifi- 

 cant rise. 



(10) The medial cutaneous was stimulated eleven times (three subjects): 

 three times there was no change in the deep-pressure threshold, eight times 

 there was a significant rise. 



Elevation of thresholds was never produced by a current too weak to evoke 

 a tingling sensation; only when the throbbing reached a certain degree of 

 intensity did elevation of thresholds occur; and the rise in threshold varied 

 directly as the intensity of the tingling. Moreover, stimulation of a cutaneous 

 nerve proximal to a procaine block evoked tingling in the anesthetized skin 

 and raised the deep-pressure threshold beneath it, whereas stimulation distal 

 to the block evoked no sensation and did not elevate the deep-pressure thresh- 

 old. Evidently masking depends upon the sensation of tingling. 



This leads us to inquire concerning the throbbing or tingling felt in the 

 cutaneous area supplied by a nerve under electrical stimulation. That this 

 sensation, though felt in the skin, is not caused by retrograde stimulation of 

 end-organs therein (with or without the liberation of chemicals) is shown by 

 our observations just mentioned, that (a) stimulation proximal to a procaine 

 block elicited the sensation exactly as with an unblocked nerve (though the 

 block isolated the end-organs from the stimtdus), w^hereas (b) stimulation 

 distal to the block elicited no sensation. In 1936 Lewis" published a description 

 of similar experiments yielding sensory results identical with those listed as 

 (a) and (b) above, but without mentioning our work, the preliminary accounts 



