150 F. H. SCOTT. 



measured, only two are tabulated. The number of hours before the 

 root became inactive in these earlier experiments varied from 8 to 40. 

 Many other experiments were also nearly completed, viz. the root was 

 giving very short replies after long rests, when some accident to the 

 root put an end to the experiment. These also are not tabulated. 

 The above table shows that for a cut root to become inactive in the 

 short time of these experiments there must be activity. It tends also 

 to show that only a certain amount of movement can be obtained 

 from a cut root, no matter over how many hours the stimulation is 

 extended. 



The above experiments show that in a comparatively short time it 

 is possible through activity to bring the reflex arc into such a condition 

 that it no longer gives a reaction on stimulation of the dorsal root. 

 The following possibilities seem to present themselves. 



(1) The muscles are fatigued. 



(2) The cells in the cord are fatigued or dead. 



(3) The root itself is dead and non-conducting. 



(4) Or, as I believe, that all the substance which passes between 

 the root and the cells in the cord, and excites the latter, is used up. 

 The root is therefore ineffective. 



In order to guard against either of the first two possibilities the 

 operation was performed with the least possible loss of blood, and the 

 skin kept well moistened the whole time. This latter is most essential, 

 especially if the breathing be feeble. 



The condition of ineffectiveness of the dorsal roots, due to their 

 prolonged stimulation, was not due to fatigue in the muscles, since 

 direct stimulation of the sciatic still caused contractions. 



On the probable assumption that the motor cells supplying the limb 

 may all be set in action by one dorsal root, it is clear also that the seat 

 of fatigue is not in these motor cells, since movements of the limb were 

 still obtained reflexly by stimulation of other nerve roots (cp. Figs. 8 

 and 9), and indeed occurred usually on release of the animal from 

 its extended position, and also at times without any obvious stimu- 

 lation. 



The total amount of stimulation had also not injured the conducting 

 property of the fibres. This, I think, is shown by the fact that after 

 prolonged continuous stimulation the roots are still effective if a rest be 

 allowed. Thus in three cases the roots were stimulated continuously 

 for 2, 3|, and 5 hours. After a rest ( to 1 hour) the root in each case 



