OX THE MAMMALIAN NERVOUS SYSTEM. 409 



electrical excitation of the fibres of the cord itself. We have, however, used for the 

 sake of control, a method which did not involve such stimulation, that, namely, of inject- 

 ing a dose of a 1 per cent, solution of acetate of strychnia sufficient to ensure toxic effect. 



Under those circumstances, whether the upper or lower end of the experimental 

 tract is connected with the galvanometer, marked electrical changes, evidently 

 excitatory, are produced whenever by touching the afferent nerves of the experimental 

 tract a strychnia convulsion is evoked. Hence the impulses thus generated in the 

 cells of the cord pass both up and down along the nerve fibres. As to the channels 

 in which they pass, we can only say that since a section of the whole ventral or 

 anterior portion of each half of the cord did not sensibly diminish the amount of the 

 electrical changes, whilst a section of the whole dorsal or posterior portion of each 

 half of the cord did notably diminish the amount, it would seem that these channels 

 along which the discharge of the cells passes are situated in the dorsal half of the 

 cord, that is, in the posterior or dorsal third of the lateral columns, the posterior 

 columns, and the posterior horns. 



In another experiment of the same general kind, we divided the upper end of the 

 cord into two halves, dorsal and ventral, as described in the method of operative pro- 

 cedure. (Chapter III., Section 2.) We then connected each half with the galvano- 

 meter electrodes, and observed the amount of the electrical changes in each during 

 strychnia spasms. The changes in the dorsal half were very much more marked than 

 those in the ventral (anterior) half, thus not only confirming our previous conclusions 

 that the nerve channels by which the impulses were conducted were situated in the 

 dorsal half of the cord, but also suggesting novel considerations as to the source and 

 direction of discharges of nerve energy in the cord. (See Chapter XL) 



This experiment being i-ather framed to control our method than to ascertain 

 channels of discharge, must not however be considered as conclusive. 



Finally, it will be noticed that we do not attempt to differentiate between the 

 different columns of nerve fibres which are situated in the lateral column, direct 

 cerebellar, antero-lateral, pyramidal, &c. 



We will now pass on to consider the electrical changes evoked in the cord, not by 

 stimulation of its own fibres, but those of its nerves. 



MIHCCXCI. i;. 



