268 SOME CHAPTERS ON THE 



Frohlich made a further advance, though before his results can 

 be considered in this light it is necessary to make a very important 

 assumption, viz. that the effect of anaesthetics (ether, chloroform, 

 &c.) is the same as that of cold, and that the lengthening of 

 the " critical interval " or " refractory period " due to all these 

 agents is merely a slowing down of the processes occurring in a 

 \ nqrmal nerve in the body. 



If this is granted, Frohlich's experiments formed a very interest- 

 ing example of fatigue. He took a nerve which was in a definite 

 state of anaesthesia, and stimulated this with induction shocks 

 which followed each other at an interval known to be a little 

 longer than the " critical interval." The attached muscle served 

 as the indicator. When the nerve was excited the muscle at first 

 fell into tetanus. This is only what might be expected ; the suc- 

 cessive stimuli each gave rise to a separate impulse, and these 

 fused at the muscle. But as the excitation continued, the tetanus 

 very rapidly fell off, and the muscle ceased to contract, and 

 Frohlich's explanation is that the successive impulses fatigued 

 the nerve, so that the refractory period became longer, the rate 

 of stimulation was now less than the critical interval, each exci- 

 tation blocked the next, and so no impulse was propagated to 

 the muscle. Tait and Gunn ( 24 ) have extended these observations, 

 using Yohimbin lactate as the anaesthetic. They find that this 

 substance has in some respects the same action as other anaes- 

 thetics, and they are able to confirm Frohlich's results and add 

 some interesting details. There is little doubt, therefore, that 

 under the action of reagents of this class nerve shows fatigue (and 

 in all probability Waller's ( 25> 26 ) experiments with proto-veratrine 

 and aconitine come under this heading), and if the preliminary 

 assumption be accepted, it could be deduced from these observa- 

 tions that nerve fibres even in the body are fatiguable, 1 and 

 only do not show this property under ordinary conditions because 

 the processes of repair are so rapidly carried out ( 27 ). 



IV. REGENERATION OF NERVE FIBRES 



The effects of section of a nerve are known to every student, 

 and there is a general agreement amongst those who have experi- 

 mented on the subject as to the nature of the process. This may 



1 For a different method that also leads to this conclusion, see Thomer (*'). 



