20 Mr. F. Gotch and Prof. Victor Horsley. [Nov. 15, 



division of which indicated an actual movement of ^ of a milli- 

 metre. After we had found that the electrometer, when connected 

 with the transverse and longitudinal surfaces of the sciatic nerve of 

 the toad, showed a response of one division following the application 

 of a single stimulus, whether electrical or mechanical, we proceeded 

 to the examination of the sciatic nerve in the rabbit, cat, and monkey. 

 For these experiments the animal was in every case kept under the 

 influence of ether, which was maintained throughout the whole experi- 

 ment, and the animal was killed before recovery. The sciatic nerve 

 seemed for many reasons the most suitable of the mammalian nerves. 

 It can be quickly prepared for 7 or 8 cm. in length ; its nutrition is 

 well preserved, since the arteria comes nervi ischiadici can be left unin- 

 jured, and its diameter lessens the dangers of drying. 



The nerve, having been rapidly prepared and bathed in warm saline 

 solution, 0'6 per cent., was ligatured low down in the thigh, the liga- 

 ture including the popliteal trunks. It was then divided on the 

 peripheral side of the knot, and raised in air so as to be at right 

 angles to the limb. One kaolin pad of a non-polarisable electrode 

 was applied to the cut end, and another to the longitudinal surface at 

 a distance of 1'5 cm. A pair of sheathed exciting platinum electrodes 

 2 mm. apart, was then applied to the trunk of the nerve 6 cm. 

 centrally from the nearest leading-off electrode, i.e., opposite the 

 sciatic notch. The exciting stimulus was obtained by the break of 

 the current of a single Callaud cell supplying the primary coil of a 

 dn Bois-Reymond inductorium graduated by Kronecker. The break 

 shock produced in the secondary coil by this means was so feeble as 

 to be barely perceptible on the, tip of the tongue when the secondary 

 coil completely covered the primary. The break was effected by the 

 spring rheotome, which opened a fixed key at a definite point in its 

 course. The electrometer was connected with the non-polarisable 

 electrodes by a circuit which included the usual compensator. By 

 means of a switch the electrometer could be cut out, and the circuit 

 made to include a high resistance galvanometer, which .also revealed 

 the single variation. The two instruments could be thus readily com- 

 pared. The excursion of the mercury of the electrometer was ascer- 

 tained both by direct observation in terms of the divisions of the 

 micrometer eyepiece, and by photographing the projected capillary 

 upon a moving sensitive plate ; in the latter case the capillary was 

 magnified 100 times. The results of our observations are briefly as 

 follows : 



The mammalian nerve showed a well-marked difference or demar- 

 cation current, that is to say, the electrode upon the longitudinal 

 surface was notably positive to that on the cut end. The movement 

 of the mercury corresponding to this difference amounted in some 

 cases to 60 divisions of the micrometer, and is shown in fig. 1 pro- 



