464 



MESSRS. F. GOTCH AND V. HORSLEY 



with the 4th, which, as the figure of the plexus shows, possibly furnish some, 

 though a very small proportion, of the efferent fibres of the sciatic nerve. 



The results of these two experiments are, therefore, not completely to the point, 

 but they are interesting as showing the increase in the relative size of the effects 

 obtained with excitation of the posterior column on the opposite side of the nerve, 

 and of the lateral column on the same side, in comparison with those evoked from the 

 posterior column of the same side. 



The section of these posterior roots has thus cut down the preponderating effect 

 obtained with excitation of the direct fibres in the posterior column. 



ELECTRICAL Changes in the Sciatic Nerve after Section of the 6th and 7th Lumbar 

 and 1st Sacral Posterior Roots on the Left Side. 



The excitation of the anterior columns produced no effect. 



The results are, however, probably mixed, as will be seen by reference to the 

 experiment on the remaining animals. 



In these all connections of the sciatic nerve with the cord, except the anterior 

 roots, were divided ; the interesting fact then came to light that, even with a strength 

 of stimulus above that employed in the previous experiments, very small electrical 

 effects were evoked in the nerve by cord excitation, these being evoked by stimula- 

 tion of the posterior column of the same side and the lateral of the same side. When, 

 however, the strength of stimulus was increased very markedly, effects were produced 

 which were more marked in the case of the lateral. It is not, therefore, until the 

 intensity of the stimulus is far beyond the limits hitherto used that any marked nerve 

 effect is produced by the passage of impulses from the cord down efferent nerve 

 fibres. 



This is illustrated by the following experiment upon a Cat (209), the cord being 

 cut at the llth dorsal, and all the posterior roots on the right side divided as 



