266 SOME CHAPTERS ON THE 



III. FATIGUE 



The apparent absence of fatigue in nerve, which is one of the 

 earliest phenomenon that the observer meets' with and the student 

 hears discussed, is philosophically considered a very curious pro- 

 perty of these structures, and has both a greater importance and 

 a 'closer connection with what has gone before than might at first 

 sight be supposed. The fundamental experiments are known to 

 every one. Medullated ( 17> 18> 19 ) and non-medullated ( 20 ) nerves 

 can be stimulated for hours, the impulse being blocked (by cold, 

 ether vapour, the constant current and so forth), and when the 

 block is removed the end organ responds to an amount apparently 

 identical with that with which the observation began. As far as 

 this class of experiment goes, no fatigue can be detected, and 

 even in isolated nerve, completely removed from any possibility 

 of the natural circulation being maintained, Waller ( 8 ) has shown 

 that fatigue is not found. 



Various explanations could be found of this result. The most 

 obvious, that as no fatigue can be detected there is in reality none, 

 would be, if true, a most remarkable phenomenon. It would 

 mean that a nervous impulse was conducted along a living 

 structure, that connected with this was an electrical change of a 

 measurable amount, and yet that no energy was made use of in 

 the process, a phenomenon unlike any other occurring in the body. 



The next explanation, and the one that seems the most pro- 

 bable, is that although there is a certain amount of fatigue, and 

 a certain expenditure of energy, that the loss is very quickly made 

 good, and the process of repair is so rapid 1 that even between 

 induction shocks following one another at 500 per second (and none 

 of the induction coils used for the first class of experiment ran 

 at anything like this rate) there is time for the nerve to recover 

 its initial state. 



There arose at one time a curious little controversy of which 

 a short account may not be out of place. Waller ( 8 ) made the 

 suggestion that the rapid repair just referred to might be due to 

 the medullary sheath acting as the storehouse of reserve material, 



1 Other examples of very rapid repair of tissues that admittedly show fatigue 

 could be quoted. For example, the wing muscles of insects contract about 300 

 times per second, and continue in action for hours at a time, yet no one imagines 

 that they are incapable of fatigue on this account. 



