PRODUCED BY A CONSTANT CURRENT. 19 



the nerve, and also in the extremely short piece of nerve lying 

 between the paper and the electrodes, are therefore precluded. 



The stimulation experiments were arranged in the following 

 order. It was ascertained what strength of mechanical stimulus 

 would produce a contraction of a suitable magnitude, that is, a 

 moderately strong contraction with stimulation in the neigh- 

 bourhood of the positive pole, a moderate or weaker one with 

 stimulation near the negative pole. This having been found, the 

 metronome was set in motion, and the muscle had now to trace 

 out about half a dozen contractions on the cylinder of the 

 myograph. Thereupon, the metronome continuing to open and 

 close the current to the electromagnet, the polarising current was 

 at once closed, and the muscle had again to trace out five or six 

 contractions. After this the polarising current was opened, and 

 half a dozen muscular contractions recorded uninfluenced by the 

 polarising current. Following the same order, I continued the 

 experiment for some time, the number of repetitions depending, 

 partly on the endurance of the nerve, partly on the purpose for 

 which the experiment was undertaken. At the same time the 

 strength of the polarising current was sometimes varied. Every 

 experiment relating to change of excitability under the in- 

 fluence of the current, was preceded and followed by an experiment 

 in which the mechanical excitation acted alone. 



Throughout each experiment the mechanical excitation continued 

 to act in the order given to it. By this arrangement I could 

 study the course of the changes of excitability more closely 

 than in any other way at my disposal, as well while the current 

 was closed as when it was open. The metronome interrupted the 

 current to the electromagnet three times in two seconds on the 

 average. I was unable to determine more minutely the relations of 

 excitability during the first moments after the opening and closing 

 of the current. This, however, lay outside my purpose, which 

 was to investigate the persistent - changes of excitability during 

 closure of the current and after its discontinuance. 



To show that the nerve completely tolerates mechanical ex- 

 citation when thus conducted, I made a number of experiments 

 with mechanical stimulation alone. These proved that the nerve 

 possesses a much greater toleration of mechanical stimulation than 

 has hitherto been supposed, and greater than my own earlier ex- 

 periments had shown 1 . Besides, they showed that the contractions 



1 Tigerstedt, Studien iiber mechanische Nervenreizung, i, Helsingfors, 1880, p. 34. 



C 2 



