20 CHANGES OP EXCITABILITY IN NERVES 



decline regularly and slowly when mechanical excitation is con- 

 tinued. This proves that mechanical stimulation is in reality quite 

 specially adapted for the study of changes of excitability in nerves. 

 In consideration of the importance of this matter, I shall here cite 

 one or two of these experiments. 



Experiment A. Distance from the muscle of the point of stimula- 

 tion (plexus) 39 mm. ; position of the sliding weight on the arm of the 

 lever 22 ; 3 stimulations in 2 seconds; number of stimulations 420. 



Experiment B. 1 . Distance from the muscle of the spot stimulated 

 (plexus) 42 mm. ; position of the sliding weight on the lever arm 25 ; 

 no stimulations in one minute ; number of stimulations 330. 



2. The same nerve. Distance of the spot stimulated from the 

 muscle 26 mm.; rhythm and strength of the stimuli as before; 

 number of stimulations 139. 



The muscular contractions were in some experiments recorded on 

 a registering apparatus of Marey's, provided with Foucault's regu- 

 lator ; in others on a recording cylinder constructed by Loven, which 

 last was worked by a water-motor with the greatest regularity. 



I used an elastic recording lever constructed by Love*n, which 

 magnified the muscular contractions 3*5 times. 



The experiments were continued from October 1881 up to 

 January of this year, and were made on specimens of Rana 

 esculenta which had been sent in autumn from Berlin. Through- 

 out each experiment the polarising current was constantly in one 

 direction. In these investigations it was important to enquire 

 into the changes of excitability of the nerve evoked by a current 

 with a certain fixed direction. In order that the result should 

 come out as clearly as possible, it was imperative that the direction 

 of the current should remain unaltered for each experiment. 

 Considering how delicate and easily destroyed the nerve substance 

 is, one must use the greatest circumspection to avoid having 

 it more destroyed or injured than is indispensably necessary for 

 the purposes of the experiment. If, however, the direction of a 

 constant current is frequently changed, it may easily happen that 

 the results are disturbed. I am convinced for my part that the 

 numerous irregularities which many enquirers have found, depend 

 to a considerable extent on their having too frequently changed 

 the direction of the current. In every experiment the conditions 

 must be made as simple as possible, and it is better to use several 

 nerves than seek to get everything from one nerve. Such ex- 

 periments may often give no results. 



