NATURE OF THE NERVE IMPULSE. Ill 



the end-organ muscle, gland, etc. is subject to fatigue, and 

 must therefore be protected from constant activity. From time 

 to time or at the end of a long period of stimulation the block is 

 removed and it is noted whether or not the end-organ for in- 

 stance, the muscle gives signs of a stimulation. The removable 

 block has been obtained by the action of a polarizing current, by 

 cold, by narcotics, by curare, etc. Using curare, for instance, 

 Bowditch* found that the sciatic nerve might be stimulated continu- 

 ously by induction shocks for several (four to five) hours without 

 complete fatigue, since as the curare effect wore off the muscle 

 whose contractions were being recorded (M. tibialis ant.) began 

 to respond, at first with single and finally with tetanic contractions. 

 The curare in this case may be supposed to have blocked the nerve 

 impulse at the motor end-plate and thus protected the muscle 

 from responding until the lapse of several hours, although the 

 nerve during this entire time was conducting tetanic stimuli. This 

 experiment has since been repeated by Durig,f who has made use 

 of the fact that the effects of curare can be removed within a few 

 minutes by the salicylate of physostigmin. Durig stimulated the 

 nerve for as much as ten hours and then upon removing the curare 

 block found from the contraction of the muscle that the nerve 

 was still conducting. Edesf and others have shown that the 

 same result is obtained when the nerve is tested by a capillary 

 electrometer instead of by the response of an end-organ. Under 

 such conditions the nerve exhibits an undiminished action cur- 

 rent, although constantly stimulated by tetanizing shocks from an 

 induction apparatus. Brodie and Halliburton have found that 

 the non-medullated fibers in the splenic nerve can also be stimulated 

 for many hours without losing their power of conduction, that 

 is, without showing fatigue. Many other observers have obtained 

 similar results, which have confirmed physiologists in the belief 

 that the nerve fibers may conduct impulses indefinitely, or, in 

 other words, that their normal functional activity may be carried 

 on continuously without fatigue. If this belief is entirely correct 

 it would place the nerve fibers in a class by themselves, since all 

 other tissues that have been studied show evidence of fatigue when 

 kept in continuous functional activity. Moreover, if this belief is 

 entirely correct it would imply that the conduction of an impulse 

 in the nerve fiber is not associated with a consumption of material, 

 a metabolism, and in this respect also the functional activity of 

 the nerve would be placed in contrast with that of other organs. 



* Bowditch, " Journal of Physiology," 6, 133, 1885. 



t Durig, " Centralblatt f. Physiol.," 15, 751, 1902. 



J Edes, "Journal of Physiology," 13, 431, 1892. 



Brodie and Halliburton, "Journal of Physiology," 28, 181, 1902. 



