146 F. H. SCOTT. 



limited 1 . Sherrington 2 has also noted that the reflexes obtained from 

 a given place of the skin soon cease if the stimulus be repeated 

 frequently, although similar reflexes may still be obtained from neigh- 

 bouring areas. Bethe 3 has also noticed that a cut nerve in frogs 

 loses its sensitiveness much more rapidly if it be subjected to stimula- 

 tion than if it be left at rest. If all these results do not show the 

 discharge of some substance out of the nerve, they at least emphasise 

 the great difference in the behaviour of nerves when they merely 

 conduct and when they conduct and excite other cells. 



We know, chiefly from the work of Mosso, that the central is much 

 more readily fatigued than the peripheral nervous system, and it ought, 

 therefore, to be possible in the former within the limits of a fairly short 

 experiment to localise the actual seat of fatigue, and to determine the 

 factors necessary for recovery of such a part. The stimulation of 

 different parts of the motor tracts affords some evidence in this regard. 

 Levy 4 experimented on the amount and nature of the fatigue, as judged 

 by the muscular movements, resulting from stimulation of different 

 parts of the motor tract He noticed that, on cutting the cord, the 

 recovery from fatigue caused by stimulation of the lateral columns lower 

 down is much slower than when the cortex itself was excited before 

 division of the cord. I believe this is due to the severance of the 

 synapse from its cells of origin, but, of course, the alteration in blood 

 supply must also be considered. 



To decide if there is any recovery after complete fatigue of the 

 severed fibres connecting the brain and cord I made some experiments 

 on the frog. The frog was chosen, since in this animal it is possible to 

 eliminate differences in conducting power or excitability due to changes 

 in temperature. The cord was cut and electrodes applied to its upper 

 end. My experiments showed that it is possible by repeated stimulation 

 to bring these fibres into such a condition that they will not give any 

 more response on stimulation, and such condition remained permanent 

 as long as the frogs lived or were kept (6 to 36 hours), but during all 

 this time stimulation of the central end of the sciatic caused reflexes, 

 thus showing that the fault does not lie in the discharging (motor) cells. 



As.it was impossible to limit the stimulations to one side of the cord, 



1 Cp. Waller. Brit. Med. Journ. n. p. 135. 1885; Brodie and Halliburton, This 

 Journal, xxviu. p. 181. 1902, and papers there quoted. 



2 Phil. Trans. Roy. Soc. London, oxc.B. p. 165. 1898 ; and S chafer's Text Book, u. 

 p. 831. 1900. 



3 Allg. Anat. v. Physiol. des Nervensy stems. Leipzig. 1903. p. 164. 

 * This Journal, xxvi. p. 210. 1901 ; and xxvm. p. 1. 1902. 



