Page:Proceedings of the Royal Society of London Vol 60.djvu/272

246 Dr. W. P. May. On the Segmental Representation stimulation of a point 1 mm. centrally or laterally to a given point often produced an entirely different resulting movement or no movement at all, which fact is clearly of much importance in showing that, with the above strength of current, the restriction of the stimulus to one point can be accurately attained.

As a means of controlling the observations derived from electrical excitation, mechanical stimulation was sometimes employed in examining the nerve roots, and was obtained by pinching the tissues with fine forceps. The results were precisely the same as those gained by electrical stimulation.

(a) Area Excitable.—The excitable area of the surface of the cord itself is the postero-external column. Stimulation of the column of Goll produced no movement except in the lower lumbar region, where that column is either very narrow or practically absent, and where, presumably, the effect was due to the stimulus directly affecting the fibres of the postero-external column.

(b) Unilaterality.—In the large majority (91*5 per cent.) of experiments on animals (dog, cat, monkey) the fact was strikingly evident that the movements produced were limited to the side stimulated.

(c) Vertical Extent of the Spinal Cord in the Dog from ivhich movement in the Lower Limb can be obtained.—In the dog, movements in the lower limb can be produced from stimulation of Burdach’s column from the upper border of the 13th dorsal segment to the lower border of the 1st sacral segment, and from the results obtained it will be seen that the various areas in the postero-external column, the stimulation of which on the surface of the cord produces movements in the limbs, anus, and tail, all overlap one another, but that on the whole the hip area is a little nearer the cerebrum than that lor the knee, the area for the knee more proximal than that for the foot, and so on.

(d) Effect, of Transversely Dividing the Cord above the Lumbar Enlargement.—The only effect observed to follow such separation of the cord from the brain, upon the movements elicited as above described, was one of increased excitability. The limits described were found to prevail precisely, and the cord was excitable quite up to the level of the section.