43G 



MESSRS. P. GOTCH AXD V. HORSLEY 



SECTION of posterior column on same side as nerve at llth to 12th dorsal vertebra 



The above experiments made upon five Cats give results, which, as is seen, differ 

 considerably in several instances, the deflection before section being in some cases 

 four times as great as that after section ; in others not twice as large. The latter is, 

 however, the case when owing to some circumstance the stimulus evoked very large 

 effects (see Cats IV. and V.) including strong reflex movements. If, however, we mass 

 together all the results obtained in the two sets of animals, the average reduction of 

 effects due to section of one posterior column would amount to about 60 per cent, 

 of the total effect obtained in the normal condition. Hence it would seem that one 

 posterior column is the main channel by which the entering nervous impulses proceed 

 from the lumbar to the dorsal cord. 



The difficulties involved in this series of experiments will be still more evident 

 when we turn to the influence of the section of only the opposite posterior column 

 upon the cord effect. 



C. Section of the Posterior Column of the Opposite Side to the Nerve Excited. 



In these experiments we are for the first time confronted with the remarkable fact 

 that in consequence of an intervening section the stimulation of the nerve is some- 

 times followed by an increased effect. (See also Chapter VIII., Section 9, B., p. 395.) 

 Since the section has cut off at least some channels of communication between the 

 lower and upper parts of the cord, and presumably, therefore, has blocked the paths 

 of some, even though few, nerve impulses, such a rise must be attributed to the 

 greater intensity of the effect evoked in the remaining channels, whether nerve fibres 

 or nerve .cells, and the cord must therefore be considered to be hyperexcitable. 



This alteration in excitability is probably associated with the phenomenon of hyper- 

 aesthesia observed by FODERA and SCHIFF to follow operative inter-fence with the 



