388 MESSRS. F. GOTCH AND V. HORSLEY 



ported by the series of experiments to be next detailed, in which the result of 

 intervening localised section of columns upon the electrical effects evoked by excita- 

 tion of the same is set forth. 



SECTION 8. THE ELECTRICAL CHANGES IN EACH HALF OF THE LONGITUDINALLY 



DIVIDED CORD. 



The question as to what amount of the electrical effects, and thus of the excitatory 

 processes underlying these, when evoked by stimulation of one column, is due to 

 changes confined to that column only, is one of such importance in respect to the 

 well-known views as to conduction by the different groups of fibres in the cord that it 

 seemed advisable to approach this subject by particular experiments. In the case of 

 the changes in the cord following excitation of the cortex, we had found that it was 

 possible to split the cord longitudinally without destroying the excitability of the 

 two halves, and so to obtain evidence of unilateral localisation of effect. This seemed 

 the most straightforward means of getting information as to localisation when the 

 columns of the cord were the seat of the excitation ; at the same time we felt that 

 the operation of longitudinal division must in all probability seriously affect the 

 functional continuity of the posterior columns, whose excitation in the Cat, as the 

 foregoing experiments have shown, is productive of such marked results. To these 

 experiments attention must now be given. 



We have only performed two successful experiments ; both upon the Cat. 



In the first the cord was divided at the 9th dorsal and at the 4th lumbar 

 vertebrae. The upper dorsal end of the fragment was prepared for excitation, the 

 lower lumbar end was freed and split in a manner similar to that employed in the 

 cortical experiments. (See fig. 16.) Each half was connected with a pair of non- 

 polarisable electrodes, as in those experiments, and either pair could be switched into 

 the galvanometer circuit and its electrical changes observed. The general arrange- 

 ment of the circuit in this case is shown in fig. 1. 



When the columns were excited for 5 seconds with the secondary coil at 2000, 

 and the right portion of cord investigated, then- 

 Excitation of the right lateral produced an effect of 31, 

 left no effect. 



On the other hand, 



Excitation of the right posterior produced an effect of 53, 

 ,, ,, left ,, ,, ,, 15. 



The left portion of cord was now investigated and the same strength of stimulus 

 employed. It was found that 



