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



exciting current, it could be obtained after ligature of the nerve, and 

 when thus obtained its character, as shown by the movement of the 

 electrometer, was unlike that of the excitatory variation, both to the 

 eye and in the photograph (compare figs. 1, 2, 3, Plate 1). 



(3.) An excursion similar to that we are considering could be pro- 

 duced by mechanical excitation. 



There is thus no doubt that the movement we obtained and 

 photographed was due to the electromotive change which accom- 

 panies the propagation of an excitatory state along the mammalian 

 nerve when this state is evoked by the application of a single 

 stimulus. 



Having thus assured ourselves of the accuracy of the method, we 

 now proceeded to ascertain whether the instrument would reveal the 

 existence of similar electromotive changes if it was connected with 

 the nerve or with the spinal cord, and an epileptic convulsion pro- 

 duced by excitation of the cortex cerebri. 



PART II. Excitation of the Cortex Gerebri. 



A. Mixed Spinal Nerve connected with the Electrometer. In two 

 cases we have connected in the manner described in Part I the 

 sciatic nerve with the electrometer, and have then exposed by a 

 small trephine opening the so-called motor cortical centre for the 

 lower limb. This we then excited by a very weak but adequate 

 furadic current. So far, however, we have not been able to detect 

 any movement in the mercury, although the muscles of the investi- 

 gated limb supplied by the anterior crural nerve were thrown into a 

 state of active convulsion. It is probable that the character of the 

 neural disturbances in the mixed nerve may be best studied by 

 investigations which we shall shortly undertake upon the electro- 

 motive changes in the muscles. 



B. The Spinal Cord connected with the Electrometer. The experi- 

 ments, the results of which are now to be briefly detailed, were made 

 in the following manner : 



The spinal cord of the etherised animal (cat and monkey) was 

 exposed in the lower dorsal region for about 4 cm., and as low down 

 as the upper end of the lumbar enlargement. Great care was taken 

 by bathing with warm saline to guard as much as possible against 

 the dangers of error due to cooling and drying. The dura mater 

 having been split longitudinally, a strong thread was passed round 

 the spinal cord at the lower limit of the part exposed. It was tied 

 firmly and the cord divided below the knot. By successive division 

 of the two or three roots exposed in the intervertebral foramina, the 

 cord was easily raised from the neural canal and suspended in the air 

 without any great interference with the circulation in the longitudinal 

 vessels. 



