400 



MESSRS. F. GOTCH AND V. HORSLEY 



that of the nerve in character, but owing to the difficulty of keeping the root protected, 

 and at the same time insulated, the amount of the effect, and, presumably, the 

 excitability of the root, declined, especially in one Cat (341); the results, therefore, 

 are all modified by the fact, that as the " minimal" stimulus was applied first, the 

 deflection caused by the excitatory electrical root change is much larger in the case of 

 the " minimal " stimulus relatively to that of the " maximal " stimulus than would 

 otherwise be the case. 



The following table gives the results of the galvanometric observations ; each 

 deflection being produced by electrical changes in the nerve root, corresponding to the 

 localised excitation, for five seconds, with the interrupted induction current of the 

 sectional area of a special tract of the cord as indicated below. 



EFFECT in Left 7th Lumbar Posterior Root. 



It is seen that with the minimal stimulus an effect is practically only evoked by 

 excitation of the posterior column of the same side as the root ; with a stimulus of 

 greater intensity an effect is also obtained with stimulation of the posterior column of 

 the opposite side, this being one-fourth the amount of that evoked by stimulation of 

 the column of the same side. As regards the lateral columns, only once was any effect 

 in the root obtained, and that was with stimulation of the column of the same side. 



If it be remembered that the minimal effect is exaggerated in the case of the 

 posterior columns by the fact that their stimulation coincided with the fresh condition 

 of the root, it will be seen that as far as the relations between the effects due to 



