302 Prof. F. Gotch and Mr. G. J. Burcli. Electrical 



a magnification of 416 diameters. The velocity of the transit of the 

 plates in the experiments now described varied between 14 and 

 70 cm. per second ; it was determined in every instance by record- 

 ing upon the plate the vibrations of a tuning fork having a period of 

 500 per second. 



The sciatic nerves of large specimens of R. temporaries were used 

 in all the experiments, and the present results were obtained during 

 the winter months, i.e., from October to March. 



The prepared nerve was placed in a moist chamber kept at from 

 4 to 6 C. ; the chamber contained non-polarisable electrodes for the 

 electrometer and polarising connections, and a pair of exciting- 

 electrodes. In every case the nerve was excited by a single stimulus 

 applied to the sciatic plexus 20 to 30 mm. from the nearest of the 

 electrometer contacts. 



The form of stimulus usually employed was a relatively feeble 

 induced current caused by the opening of the primary circuit of a 

 standardised induction coil, which included one Dariiell cell; the 

 opening was effected by the pendulum motor and the primary coil 

 contained no core. Each single stimulus of this type produces a 

 movement of the meniscus when the electrometer contacts are 

 suitably arranged upon the nerve. The movement is in some cases 

 perceptible to the eye when the highly magnified image is projected 

 upon a screen, but in many instances is only visible after the develop- 

 ment of the photographic record. That the movement was not due 

 to an escape from the exciting circuit is shown as follows : The 

 direction and character of the movement is unchanged whatever the 

 direction of the exciting current; the escape, if present at all, is 

 clearly indicated in the record as a rapid displacement of the meniscus, 

 preceding by a distinct interval the larger movement which is here 

 referred to ; such antecedent escape excursions remain unmodified in 

 character under conditions which materially affect both the larger 

 movement and the physiological condition of the nerve (polarisation, 

 C0 2 , &c.) ; the escape, if present, is increased by augmenting the 

 intensity of the exciting induced current, whilst the larger change 

 reaches a maximum with a certain intensity of stimulus ; finally, the 

 larger movement is obtained by mechanical excitation such as the 

 single tap of a light hammer arranged after the method of v. Uexkiill.* 

 In order to facilitate the description of the excursions obtained, 

 selected photographs have been projected upon a screen and the out- 

 lines of the variation in the level of the meniscus carefully traced ; 

 a number of different curves are thus brought into juxta-position. 

 A. reduced copy of this is given in fig. 1. Some of the actual records 

 will, it is hoped, be produced in a more extended communication, 

 but the curves given in the figure are not merely faithful reproduc- 

 * v. Uexkiill, ' Zeils. f. Biol.,' vols. 31, 32, 1895. 



