284 MESSRS. P. GOTCH AND V. HORSLEY 



any danger of strangulation when the freed portion of cord was subsequently raised. 

 On reflection of the dura, a ligature was cautiously passed around one end of the 

 exposed cord, the end chosen varying in accordance as it was desired that the 

 observed portion of cord should be in communication with the brain or with the 

 sciatic nerves. If the former, then it was knotted gently -round the lower end so as 

 to securely close the vessels, and the cord divided immediately below the ligature. 

 The (central) end was now raised by the ligature, and the nerve roots exposed and 

 divided one by one until the whole portion of the exposed cord was freed from all 

 attachment except at the upper end, where it was continuous with the central 

 unexposed region. In the case of experiments upon the cord severed from the brain 

 but in connection with the sciatic nerves, the ligature having been applied round the 

 upper portion of the exposed tract, the cord was divided on the central side of the 

 ligature and the exposed portion freed downwards in a similar manner to that just 

 described. 



(b.) Preservation of Circulation. The circulation in the exposed portion was 

 maintained as far as possible by the ligature of its cut end, including the main vessels, 

 and by keeping the cord in connection with an undisturbed portion, and avoiding any 

 strangulation of that connection. 



(c.) The Immobilisation of the Spinal Column. The fundamental importance of 

 fixing the vertebrae necessitated the employment of a special clamp. This clamp was 

 applied so as to firmly grasp in its powerful vice-jaws the transverse processes of the 

 spinal column in the immediate neighbourhood of the exposed cord. The jaws were 

 fixed on a stem, and approximated by an ordinary double screw. In order to avoid the 

 extraneous electrical effects which the presence of metal surfaces in contact with moist 

 cut tissues necessarily involves, the jaws were made of stout pieces of ivory. The 

 stem carrying them was fixed to a powerful upright attached to the experimental 

 table, and so arranged as to secure a fixation vertically above the preparation. (See 

 Plate 29.) 



(d.) Cooling and Drying. The exposed cord was kept bathed with the warm 

 saline solution until it was actually the subject of experiment, when, if it were 1 aised 

 in air, care was taken to keep steaming sponges in its immediate neighbourhood. 



(e.) Isolation. The necessity of isolation for purposes of galvanometric observation 

 will be referred to later on. This isolation was produced by raising the ligatured end 

 of the exposed portion of cord, so that the portion swung in air without pulling upon 

 its deep attachment. The electrodes, &c., were adjusted as described in the succeeding 

 sections. 



4. Division of the Exposed Portion of Cord by a Longitudinal Incision. 



For certain purposes it was desirable to observe the galvanometric effects in each 

 half of the cord independently. These were (1) the determination of the comparative 



