304 Prof. F. Gotch and Mr. G. J. Burch. Electrical 



Freshly Prepared Nerve ; both Electrometer Contacts upon the 

 Uninjured Surface. 



The nerve in these preparations was dissected out from the spinal 

 column to the knee, and the muscles below the knee were left attached 

 to the preparation. With the electrometer contacts arranged at 

 distances of 5 and 15 mm. respectively from the knee end, no resting 

 difference of potential was perceptible. A single electrical or 

 mechanical excitation of the sciatic plexus 45 mm. from the knee 

 end of the nerve causes no visible displacement in the level of the 

 mercurial meniscus, but the photographic record shows a rapid 

 excursion indicating that the contact nearest the seat of excitation 

 (proximal) is first negative and then positive to that more remote 

 (distal). The character of the rapid up and down movement is 

 indicated in curve (i) fig. 1. If the contacts are placed further 

 apart (25 to 30 mm.) the spike present in the record is more pro- 

 nounced, the ascending and descending limbs being further apart. 



Freshly Prepared Nerve ; the Proximal Electrometer Contact upon the 

 Uninjured Surface, the Distal upon a recently made Cross Section 

 at the Knee End. 



The contacts were arranged 10 mm. apart, and the well-known 

 resting difference of potential existed between them. This demarca- 

 tion difference caused a downward movement of the level of 

 the meniscus amounting in some cases to 10 cm. upon the screen. 

 It was not compensated by the use of any external E.M.F., but the 

 pressure was altered so as to bring the meniscus up again to its 

 proper position. During the presence of this permanent demarcation 

 effect each single excitation of the plexus, whether electrical or 

 mechanical, is followed by a visible displacement in the level of the 

 image. The photographic record, see fig. 1 (ii), shows a rapid 

 upward movement, followed by a prolonged tail in place of the 

 downward movement obtained with uninjured nerve, thus indicating 

 a more persistent change of the same sign as the initial one ; this 

 disappears comparatively slowly, and is of much lower E.M.F. 

 than that which produces the initial rise. 



Excised Nerve kept in the Cold from 24 to 90 hours in 0'6 per cent. 

 NaCl made with Tap-water containing Traces of Calcium Salts. 



That nerves kept in this way retain their excitability is shown by 

 the fact that if the muscles are not detached they respond to excita- 

 tion of the nerve trunks. 



On connecting such an excised nerve with the electrometer, no 



