Page:Proceedings of the Royal Society of London Vol 60.djvu/271

Rh Exposure of spinal cord.

Division of cord and isolation of segments. The cord was exposed with due observation of well-known precautions (Gotch and Horsley, ‘ Phil. Trans.,’ vol. 182, B, 1891). In some cases the spinal cord and roots were stimulated at first in continuity. In others, before proceeding to experiment, the spinal cord was completely divided at from two to eight segments above the part experimented upon. The spinal roots were divided as detailed in the paper.

Apparatus.—A single Daniell cell was used which supplied a Du Bois Reymond’s inductorium of the usual type, the secondary coil being 20 cm. or more from the primary. The electrodes attached to the secondary coil consisted of closely approximated (1 mm.) platinum points. The duration of excitation was, as a rule, momentary, and never exceeded 1—2 seconds.

(a) Excitation of Nerve Roots.—The nerve roots were raised in the air and the electrodes usually applied, so that the direction of the exciting current was transverse to the nerve fibres.

(b) Excitation of the Spinal Cord.—The surface of the cord was gently dabbed with small wool swabs, kept in warm saline solution and squeezed dry, before the electrodes were applied. The duration of excitation was always brief, rarely exceeding one second.

The value of the method may be estimated by considering the following facts. On stimulation of the surface of the spinal cord as already mentioned, movement was always elicited in the leg on the side stimulated, when the electrode was applied to the surface of the posterior column, but never, as far as I was able to see, could movement be obtained by the application of this strength or even considerably greater strength of stimulus to the lateral or anterior columns, when adequate precautions (paper) were taken to prevent the direct spread of the current to the neighbouring root fibres. The movement elicited from stimulating the posterior columns was always marked and quite definite, and merely depended in intensity upon the conditions stated below. For instance, applying the electrodes to the surface of the postero-external column in the fifth lumbar segment of the dog on the left side produced lateral flexion of the spinal column to the same side, flexion and adduction of the hip, flexion of the knee and toes, and movement in the tail (flexion to the same side). But the chief result was the very local, effect which could be obtained by varying the point stimulated; thus,