376 MESSRS. P. GOTGH AND V. HORSLEY 



were limited, presumably by the anatomical relations of the paths along which they 

 were conducted, to given tracts of fibres in the different columns. We thus designed 

 our work to ascertain the scheme upon which the fibrous structure of the cord was 

 arranged, and this for both ascending and descending impulses. 



We found that the electrometer was not a suitable instrument for this investigation, 

 since with minimal stimulation its movements were too small to admit of sufficiently 

 accurate estimation, whilst the uncertainties connected with the conditions regulating 

 its sensibility rendered exact comparisons of small differences between different sets 

 of experiments impossible. We therefore used the galvanometer in all the remaining 

 experiments, obtaining with it results which could be better relied upon for purposes of 

 comparison. 



SECTION 5. ELECTRICAL CHANGES PRODUCED BY LOCALISED STIMULATION OF THE 



COLUMNS OF THE CORD. 



Plan of Experiments. 



In order to obtain quantitative comparisons between the effects evoked by localised 

 excitation of different columns in the cord, the plan adopted was to divide the cord in 

 the mid-dorsal and lumbar regions, and prepare one end of the isolated experimental 

 tract lying between the sections for connection with the galvanometer electrodes and 

 the other for excitation. The method of connection has been already fully described, 

 namely, at the cross section and the surface 1 centim. away, by means of cables, 

 under all precautions previously indicated. The preparation of the other end for 

 excitation was effected by removing about a centimetre from the end, and thus 

 exposing the cross section of the cord, in which it was possible, using the precautions 

 described in the chapter on operative procedure, to stimulate, with a pair of fine 

 platinum electrodes, the section of each column thus exposed, anterior, lateral, 

 posterior, or the grey matter. 



The experiments showed us that with moderate intensities of stimulating currents, 

 electrical effects were always produced in the observed end of the experimental tract, 

 when at the other end the cross section of either lateral or posterior column was 

 excited, but that only very small and rare effects were caused by a similar excitation 

 of the anterior columns or of the grey matter. This suggested that no continuous 

 strand of fibres united the excited portion of these latter tracts with the observed 

 portion. We shall refer to this result again later on ; since, however, the stimulation 

 of the lateral and posterior columns alone gave notable effects, we limited our excita- 

 tion in the majority of instances to these columns. 



The majority of these experiments were carried out on Cats (17 animals), but we also 

 made a considerable number of experiments on three large Macaque Monkeys. It will 

 be presently seen that the results differ in the two animals in a most interesting way. 



