FATIGUE IN NERVES. 147 



leaving the other side as a control, and since the subject can be better 

 investigated with the dorsal roots, I shall not give any fuller details of 

 these experiments. 



2. Fatigue in cut dorsal roots. 



The first series of experiments was carried out to see if a dorsal root 

 cut off from its cells of origin could be permanently fatigued. Two 

 roots were cut close to the ganglion, and one left as a control, while the 

 central end of the other was stimulated. The frog was given ether, its 

 forebrain removed by the cautery, and in some cases the cord was 

 divided below the medulla, also by means of the cautery. The laminae 

 were removed from the lower 3 or 4 vertebras 1 with scissors and the 

 roots tied proximal to the ganglia with threads and then divided. In 

 most cases the dorsal root of the 10th nerve leaving between the 

 urostyle and last vertebra was secured on both sides but in some cases 

 two roots on the same sides were used. A pair of platinum electrodes 

 were fixed on a stand above the back of the frog so that the nerve could 

 readily be removed for moistening. In this set of experiments the 

 reflex movements of the limbs were observed, but tracings were not 

 taken. Tracings of the movements of the gastrocnemius due to excita- 

 tion of cut dorsal roots were, however, made in a later series of experi- 

 ments. Some of these may be seen in the upper tracings of Figs. 1-11. 



The reflex excitability was heightened by cooling (Biedermann 3 ). 

 By adopting this precaution it is possible to evoke reflex contractions 

 with a much smaller strength of current than would be required by 

 normal frogs. One can in this way avoid all danger of spread of 

 current to adjacent excitable tissues. In most cases the frogs gave 

 reflex contractions with the secondary coil 25-50 cm. from the primary. 

 In some cases this is less than that required to stimulate the motor 

 nerves directly. The weakest possible current was always used. To 

 obtain maximal contractions it is not necessary to increase the current 

 beyond a certain point, as the contractions do not last longer nor are they 

 stronger than with the weaker stimuli. (Sherrington 3 .) 



There are variations in the type of muscular response on stimulation 

 of a dorsal root and I have seen the different types described by Wundt, 

 Nothnagel, Sherrington, Biedermann, and others in their various 



1 By snipping off the upper end of the urostyle and then inserting the point of one 

 blade of the scissors, the laminae may be removed without even opening the coverings of 

 the cord. 



2 Pfliiger's Archiv, LXXX. p. 408. 1900. 



3 Phil. Trans. Roy. Soc. London, cxc. B. p. 140. 1898. 



102 



