118 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



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 was under stimulation during this entire time. This 

 experiment has since been repeated by Durig,t 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. EdesJ 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. It must be remembered, how- 

 ever, that although the above experiments demonstrate the prac- 

 tical "unfatigueableness" of nerve fibers under ordinary conditions 

 of stimulation, there are some reasons to make us hesitate in sup- 

 posing that in these structures functional activity is entirely with- 

 out a depressing effect upon irritability. Garten has shown that 

 one nerve, the olfactory of the pike, when stimulated by induction 

 shocks, with an interval between the stimuli of as much as 0.27 

 second, gives evidence of fatigue, since its action current, as 

 measured by the capillary electrometer, diminishes in extent quite 

 rapidly, and recovers after a short rest.^ So also it has been 

 found that while a nerve deprived of oxygen, by keeping it in an 



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

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

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

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

 H Quoted from Biedermann, "Ergebnisse der Physiologie," vol. ii, part ii, 

 p. 129. 



