392 MESSRS. F. GOTCH AND V. HOKSLEY 



columns excited was, therefore, now approached by another method, that, namely, of 

 intervening sections. 



SECTION 9. INFLUENCE OF INTERVENING SECTIONS UPON THE ELECTRICAL CHANGE 

 IN THE CORD FOLLOWING EXCITATION OF THE DIFFERENT COLUMNS. 



The extent to which the electrical change in the cord following excitation of the 

 cut columns is dependent upon direct continuity of nerve fibres between the part of 

 the column excited and the part of the cord observed is more clearly indicated by the 

 experiments now to be described. 



In these the excitatory and galvanometric arrangements were similar in all details 

 to those employed in the two preceding groups of experiments ; but the experimental 

 tract had been subjected to important additional operations, some particular column 

 indicated being divided at a position intervening between the region of excitation and 

 the observed region, and the result of such division as affecting the electrical excitatory 

 change being then estimated. 



The section, the influence of which was thus investigated, was made in most cases 

 at the time of the experiment. In a few cases the section was made three or four 

 weeks beforehand, in order not only to ensure a more striking alteration of effect by 

 the degeneration of the continuous nerve tracts involved, but also to provide against 

 any transient disturbance due to the operation, affecting the excitability both of the 

 particular tract and of other nerve tracts than the one operated upon. 



Since the influence of each separate intervening section had to be studied in the 

 case of excitation evoking both descending and ascending impulses in the experimental 

 tract, the experimental results of any section naturally fall into the two groups 

 already indicated in the preceding Sections. 



(1.) Electrical Effects in the Lumbar Cord Evoked by Excitation of the Dorsal Cord. 



A. Influence of Hemisection. 



The experiments were made upon three animals (Cats), in all of which the inter- 

 vening hemisection occurred at the level of the 12th dorsal vertebra; in the first on 

 the right side, in the second and third on the left side. 



Each experiment was conducted precisely as those previously described ; that 

 is to say, the cord was divided at the 8th dorsal and 2nd lumbar vertebrae. The 

 lower end of the experimental tract was prepared for connection with the galvano- 

 metric electrodes, the upper for excitation. The different columns were first succes- 

 sively excited before the hemisection in the usual manner, and the electrical effects 

 observed. These are shown in the preceding table, see page 381, and were of the 

 kind indicated in Section 6 (6). The cord was now exposed at the 12th dorsal, the 

 hemisection made and the electrical effects of the excitation of the different columns 



