ON THE MAMMALIAN NERVOUS SYSTEM. 431 



The effect even with this strong stimulus is nearly twice as large when evoked by 

 the nerve opposite to the side of the lesion. Since, however, a considerable effect 

 is evoked by stimulation of the nerve on the same side, the use of the stronger 

 stimulus has either produced more impulses strong enough to cross the cord, or it has 

 caused a more complete discharge of the central mechanisms in the grey matter. 



The other animal, Cat (259), had a section made upon it at the 10th dorsal vertebra 

 thirty days before the observations were to be made. The section involved the left 

 lateral and the majority of the left posterior column. The subsequent examination 

 of the cord showed that the section involved on the left side the lateral column, 

 the ventral portion of the anterior column of the grey matter, and the dorsal half of 

 the posterior column ; on the right side the posterior median column. The ascending 

 degenerative changes were at the 5th dorsal traceable on the left side to a marked 

 degree in the direct cerebellar and antero-lateral tracts, and in the posterior root zone 

 and posterior median columns. A much less extensive degeneration was found to 

 have occurred in the posterior median column of the right side. 



The animal, when examined before the experimental observations, showed spastic 

 paralysis of the left hind limb, and marked diminution in the tactile sensibility of both 

 hind limb and trunk on the left side. The knee jerks were equally present on the two 

 sides. The experimental investigation, as far as it relates to the present question, 

 involved the section of the cord at the 4th dorsal (this was accompanied b;y prolonged 

 tetanus of lower limb muscles and those of the tail), the preparation of the upper end 

 of the lower fragment and the excitation of the two sciatic nerves. The excitation of 

 the right nerve evoked effects of 43 and 56, the left of 15 and 22. The sum of these 

 readings is 99 for the right, and 37 for the left side. If, as in the previous experi 

 ment, we suppose that the total sum of the two effects roughly represents the full 

 responsive change of either nerve excitation, then the effect on the side of the chief 

 lesion (hemisection) is reduced from that in the ratio of 136 to 37, i.e., 100 to 27, that 

 is, it has been reduced 73 per cent, through the hemisection. 



The result of these experiments is to show that the excitatory changes in the cord, 

 evoked by stimulation of the sciatic, are largely limited to the same half of the 

 cord as the excited nerve, the amount of limitation being such that three times the 

 effect, and presumably three times the number of nerve impulses, proceed up the cord 

 on the side of entry than that which is evoked by impulses either crossing in the cord, 

 or freshly generated by cells in response to the arrival of impulses in the grey matter 

 on the opposite side. 



Our method, however, enables us to determine not merely that the excitatory 

 effects in the cord are to a great extent limited to the side of the entering nerves, but 

 also that the effects are mainly dependent upon the unbroken integrity of particular 

 columns of fibres on this side. To observations on this point we now pass. 



