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 move- 

 ment 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. 



II. Mechanical. 



As a means of controlling the observations derived from electrical 

 excitation, mechanical stimulation was sometimes employed in ex- 

 amining 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. 



ON THE RESULTS OP DIRECT EXCITATION OF THE SURFACE OF THE 

 SPINAL CORD IN THE DOG. 



I. Gross Localisation. 



(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 experi- 

 ments 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 which move- 

 ment 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 move- 

 ments 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 

 for 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. 



