402 



MESSRS. F. GOTCH ANT) V. HORSLEY 



there are indirect fibres in the posterior columns which are not interrupted, and 

 which connect these through cells with the lateral columns. This we have already 

 seen in the case of the lateral column exclusion experiment (see p. 398), to be also true 

 for efferent impulses, hence each posterior column is indirectly connected with the 

 lateral of its own side. 



We now pass to the experiments made in similar preparations on one posterior 

 column only. 



Influence of Section of one Posterior Column. Our experiments upon this point 

 were made on two animals, but in each case with a strength of stimulus which was not 

 minimal, since, although in one animal the absolute intensity of the exciting currents was 

 that generally used for minimal stimulation (500), yet the preparation was in a hyper- 

 excitable state owing apparently to the lumbar section having hit the entrance of a 

 posterior root. That the preparation (Cat 375) was hyperexcitable at the moment 

 when the intervening section was to be made, is shown by the fact that with this 

 weak intensity of stimulus the excitation of the lateral columns gave deflections of 

 166 and 285, and that of the posteriors of 168 and 202. We endeavoured to lower 

 the excitability by more profound etherisation, but the results evidently belong to that 

 class which have been considered as evoked by maximal stimuli. The true effect of 

 minimal excitation was not, therefore, observed. The left posterior column was divided 

 in both animals at the level of the llth dorsal vertebra. 



ELECTBICAL Effect obtained in the Dorsal Cord by Excitation of Columns in the 

 Lumbar Region after intervening Section of the Left Posterior Column. 



Average effect evoked by excitation of the 



(1) Lateral columns . 



(2) Posterior columns on side of lesion . 



(3) Posterior columns on side opposite lesion 



78 



37 



131 



The interruption in the left posterior column thus did not abolish, but only reduced, 

 the electrical effect present in the dorsal cord above the interruption, when the column 

 was maximally stimulated below in the lumbar region. The amount of the reduced 

 effect is one quarter of that which can be evoked by maximal stimulation of the 

 opposite uninterrupted posterior column. The existence of even a reduced effect is 



