Response of Nerve investigated with Electrometer. 301 



carried out along these lines by Bernstein, Hermann and others, have 

 yielded results of great value. It is, however, only on the assumption 

 that the aggregate value of the successive electromotive states gives 

 at any moment a faithful representation of each component member of 

 the series, that deductions can be drawn from such rheotome observa- 

 tions as to the characters of the single electrical response. Attempts 

 have been made to obtain indications of the response to a single 

 stimulus by other methods, but without very satisfactory results, 

 As far as we know, the only permanent record of such a response is 

 that obtained by Gotch and Horsley in 1888 with the assistance of 

 Burch ; the record was that of the photographed excursion of a 

 sensitive capillary electrometer.* 



For some time the authors have been engaged in endeavouring 

 to obtain with the capillary electrometer records of the single 

 response of nerve which should be large enough not merely to- 

 indicate its occurrence but to afford data for determining its chief 

 characteristics. 



This object has been so far attained that they are now able to 

 measure the electromotive changes of nerve in response to a single 

 stimulus, by the application to the photographic records of the 

 process of analysis introduced by one of them.f (Q. J. B.) 



The electrometer employed, made especially for the purpose by 

 Burch, is more sensitive and, at the same time, more rapid in its 

 action than any they have hitherto used. The latter quality, while 

 essential to success, entails great liability to disturbance by mechanical 

 vibrations, and considerable difficulty was met with on this account. 

 The following form of support was ultimately adopted. A brick 

 pillar was built up to the level of the ground upon a concrete founda- 

 tion at the bottom of a pit 7 feet deep. On the pillar was 

 placed a stout box containing some 5 cwt. of clay and upon the box 

 three cast-iron plates, each weighing 1 cwt. Each plate was sepa- 

 rated from the one below by three bags of sawdust, the bags forming 

 supports, so arranged in opposite triangles as to come alternately 

 under the nodes and loops of the plates. The electrometer, with its 

 accompanying microscope, was fixed to the topmost plate, and was 

 thus efficiently isolated from the rest of the apparatus and from the 

 floor of the working room. 



The excursions of the meniscus were recorded by a pendulum 

 motor,;]: the image being projected by a Leitz 3 mm. objective upon 

 the sensitized plate. This was carried by the motor across the optic 

 axis in a circular arc at a distance of 125 cm. from the lens, giving 



* * Roy. Soc. Proc.,' vol. 45. 



f < Phil. Trans.,' A, vol. 183 (1892), pp. 81105. 



J See " The Capillary Electrometer in Theory and Practice," Gr. J. Burch; also 

 Burdon Sanderson, ' Journ. Phys.,' vol. 18, pp. 126 134. 



VOL. LXIII. Z 



