ON THE MAMMALIAN NERVOUS SYSTEM. 377 



The experiments all fall into two great groups, distinguished by the fact that in 

 one the lumbar end of the isolated fragment of cord was the seat of galvanometric 

 observation, whilst, in the other, the dorsal end was observed and the lumbar end 

 excited. In the first case the electrical changes are obviously due to the discharge of 

 nerve impulses down the cord, in the second to their discharge up the cord. 



We will now proceed to a detailed description, first of a typical experiment, and 

 then of the results obtained from several experiments under these two opposite con- 

 ditions, and we will take first the case of impulses descending the cord, these impulses 

 having been produced by excitation of some one column, as displayed in the dorsal 

 section of the " experimental region " of cord. The galvanometric connections having 

 been made with the lower lumbar end of this tract, electrical changes were evidenced 

 in it when "the descending impulses reached that part which was in connection with 

 the electrodes leading to the instrument. 



SECTION 6. ELECTRICAL EFFECTS EVOKED IN THE LUMBAR CORD BY EXCITATION 

 OF THE COLUMNS IN THE DORSAL REGION. 



(a.) Typical Experiments. 



Since the results in the case of Cat's cord, as mentioned in the preceding paragraph, 

 are different from those obtained with the Monkey's cord, it is desirable to separate 

 out the experiments made upon each. We will therefore describe a single typical 

 experiment and its results in the case of these animals. In order to avoid repetition, 

 the general procedure, which is the same in both animals, will be described more 

 minutely in the case of the Cat (this being taken first) than in that of the Monkey. 

 To make clear the relationship of the excitation to the galvanometric connections, 

 the actual positions in a typical case of the seat of operation and of both sets of 

 electrodes is given in fig. 10, p. 368, which represents the spinal cord of an animal 

 thus experimented upon. 



The cord of the Cat (243) was divided at the level of the 7th dorsal vertebra; it was 

 then exposed in the lumbar region for 3 centims. and divided at the level of the 

 3rd lumbar vertebra, thus isolating an experimental region which extended between 

 these two levels. The distal (lumbar) end of this isolated fragment was now ligatured, 

 and all connections having been divided, was raised in air by the thread. By means 

 of cables the transverse section was connected with one non-polarisable electrode, the 

 longitudinal surface at 1 centim. distance by a similar cable with the other. The 

 electrodes were fixed, as before, on a stand, and arranged at such a height that a con- 

 siderable length, two or three inches, of thread cable hung loosely between them and 

 the cord, all error due to mechanical displacement, as in the cortical experiments, 

 being thus guarded against. The upper end of the isolated fragment or experimental 



MDOCOXCI. B. 3 C 



