FATIGUE IN NERVES. 161 



is absent or very slight. This has been seen 24 hours after the last 

 direct reflex was obtained. These experiments show that a nerve or 

 root, being stimulated with sufficient current and still conducting, can 

 fail to activate cells capable of being stimulated. 



Another interesting feature is the character of the muscular response 

 in the two legs. Although there is usually a more or less degree of 

 similarity in the character of the muscular response in the two legs, the 

 tracing (Fig. 11) shows this is not always the case, as we can have one 



Fig. 11. Double reflex from nerve belonging to lower tracing. This side had been 

 subjected to more or less fatigue before. The drum was moving more rapidly than 

 in other tracings. Time of stimulation 1 minutes. 



side giving a tetanic contraction while the other side gives an alter- 

 nating one. 



7. SUMMARY AND CONCLUSIONS. 



It has been shown above that on stimulation of the cut dorsal roots 

 of the frog repeatedly with intervals of rest, reflex contractions are 

 obtained for a period varying from 8 to 98 hours. This variation is 

 due chiefly to the intervals of rest allowed. The total duration of 

 movement in those cases where long rests were allowed was often 

 exceeded in other cases in far shorter periods (cp. Tables I and II). 

 After this time no more movement could be obtained from such a root 

 as long as the animal lived. The duration of this period of ineffective- 

 ness varied from 8 to 72 hours. There is no reason to suppose that 

 these roots have passed into a degenerative state without recovery of 

 function as roots may be cut and left unstimulated for far longer periods 



