128 ON NEKVE-EXCITATION BY THE NEBVE-CUKEENT. 



of his electrodes of the old form covered with films of albumen 

 (which had been previously tested by the multiplier and found to 

 be free from polarity), he made and broke the nerve-current by 

 means of a mercury key. * The leg contracted at closure, and often 

 at opening ; in a few cases it contracted at opening only 1 .' 



Later, du Bois-Reymond simplified the experiment by dispensing 

 with all metallic conductors ; he placed two conducting cushions, 

 separated by an interval of a few mm. on a non-conducting support, 

 then laid the nerve upon the two cushions with transverse section 

 upon one cushion, longitudinal surface on the other ; then, by means 

 of a third cushion he completed the circuit, thus closing the nerve- 

 current 2 . Since this method allows of a rapid closure of the current 

 by the sudden application of the third cushion, but of a less rapid 

 opening by its removal, it is advisable to arrange the two cushions 

 upon which the nerve rests so as to overhang the edge of a glass 

 plate ; a vessel filled with salt-solution can then be raised quickly, 

 so that the overhanging tips of the cushions suddenly dip into the 

 fluid ; or it can be quickly lowered, so as to break the nerve-current 

 suddenly. 



Instead of the cushions, one may use blocks of saline clay, which 

 have the advantage that they may be modelled to any desired shape. 

 This is the method which Kiihne has preferred, and which I also 

 have frequently used. I kneaded the clay with concentrated salt- 

 solution, and used the same material to complete the circuit; in 

 order to protect the nerve from the action of the concentrated 

 salt-solution, I placed upon the spots, where the nerve was to lie, 

 a thin layer of clay, made with salt-solution o6/ OJ or a bit of 

 blotting-paper moistened with the same. If sufficiently excitable 

 nerves are to be had, 0-6 % solution may be used both in preparing 

 the blocks, and for closing the circuit. The contractions which 

 one obtains in this manner are, as Kiihne also states, very energetic 

 in favourable cases. The opening contractions are generally weaker, 

 or do not occur at all; sometimes, however, they are strong, as 

 indeed has already been stated by Kiihne. I may also confirm the 

 statement of du Bois-Reymond to the effect that sometimes an 

 opening contraction alone appears. 



In all cases where it is desired to compare make- with break- 

 contractions, or make-contractions taken with different lengths of 

 the interpolar region, it is advisable to employ du Bois-Reymond's 



1 Unters. fiber thier. Elektr. ii. p. 273, 1849. 

 1 Fortschritte d. Physik. iv. Jahrg. p. 314, 1852. 



