378 MESSRS. F. GOTCH AND V. HORSLEY 



tract of cord was now exposed for about a centimetre, and a fresh division made so as 

 to expose a more excitable section for stimulation. 



The portion of cord investigated showed, when connected with the galvanometer, 

 the usual resting electrical difference between the surface and ligatured cut end (see 

 Chapter IV.). 



When after compensation the galvanometer needle was steady, the exciting elec- 

 trodes, guarded by a short-circuiting key, were carefully held by one observer against 

 the cut end of one column of the cord, as described in Chapter III., every precaution 

 being taken to ensure that the surface should be dry. The key was now opened by 

 the observer at the galvanometer, and by means of the revolving paraffin key the 

 column was stimulated for a definite time (3^ seconds in this case), by a series of weak 

 induction currents (100 per second) produced by the usual magnetic interrupter, and 

 made equal and alternate by means of the Helmholtz side-wire. The intensity of the 

 exciting currents had to be adapted to the varying condition of the animal, etheri- 

 sation, &c., but the results aimed at being to stimulate the fibres in the separate 

 columns rather than to arouse the reflex activity of the cord, it was thought advisable, 

 at any rate in the commencement of an experiment, to use currents only just sufficient 

 to evoke definite effects ; such excitation will be termed here "minimal." 



In this particular case one Daniell cell was used in the primary exciting circuit and 

 the secondary coil stood at 500. The excitation of either anterior column produced 

 no electrical change ; that of either lateral produced a very distinct effect, of the usual 

 excitatory character, that is, an effect which commenced with the stimulation and did 

 not persist after its cessation. 



The effect indicated the establishment of a transient electrical state, opposed in 

 direction to that of the original resting difference. The galvanometer deflection, which 

 recorded the change, was very distinct in its commencement and termination, so that 

 its amount could be determined with accuracy. The deflection was 41 when the left, 

 and 57 when the right lateral column was excited. The stimulation, in exactly the 

 same way, of the cut end of the posterior columns produced much more pronounced 

 effects, amounting to 96 in the case of the left, and 94 in that of the right column. 

 Every precaution was taken to ensure that as far as possible the degree of narcosis, &c., 

 should be the same during the four stimulations, and an interval of 1 minute was 

 generally allowed to elapse between the successive applications of each. 



When a stronger stimulus (double the strength, coil 1000), of precisely the same 

 character and duration was employed, larger effects of the same kind were produced, 

 stimulation of the anterior regions being again followed by only a mere trace of 

 effect, that of either lateral by well-marked deflections (left 105, right 140); and that 

 of the posteriors by very large deflections (left 290, right 208). 



It will be seen that this relationship of magnitude of effect is one which is retained 

 in all the results obtained in this way by differential columnar excitation of the 

 divided cord of the Cat. 



