ON THE MAMMALIAN NERVOUS SYSTEM. 



471 



C. Influence of Section of the Posterior Column on the opposite side to the 



Nerve observed. 



RIGHT Nerve observed. 



It is seen that the effect evoked in the nerve by stimulation of the posterior column 

 of the opposite side is diminished by section. The diminution cannot be attributed 

 to general lowering of excitability since it is present in both cases, and it will be seen 

 that in the Monkey the excitability of other columns had increased. It must be due 

 to the interruption by the lesion of fibres crossing through indirect channels from 

 that posterior column. As this interruption occurs in the posterior column, it would 

 imply that there are fibres which cross over from one posterior column to the other, which 

 have a wide distribution along the cord. The diminution is due to the cutting off of such 

 fibres as descend to cross below the level of the respective sections ; the effect still 

 obtained after the section may be due to those fibres which, having crossed above the 

 level of the same, are not interrupted by the lesion. Reference to the spinal cord 

 experiments (Chapter VIII.) will show that according to our experiments the fibres 

 in the two posterior columns have very extensive indirect connections with each 

 other. 



D. Influence of Section of both Posterior Columns on the Electrical Effects evoked in 



the Nerve. 



When both posterior columns were divided, mere traces of nerve effect were 

 evoked by excitation of either column, even when the stimulus was sufficiently 

 intense to produce marked effects from stimulation of the lateral column on the same 

 side as the nerve. 



This is shown by the following experiments made upon the same two animals, the 

 nerve effect due to excitation of each different column being compared before and 

 after the intervening section of the posteriors. 



