HELMHOLTZ IN KONIGSBERG 



irritated, say at a distance of two inches from the 

 muscle, by an electric current, which also moment- 

 arily passed through the galvanometer, the move- 

 ment of the needle would indicate the instant when 

 the nerve was stimulated. Helmholtz, in the first 

 place, improved Pouillet's method by causing the 

 opening or closing shock from an induction coil to 

 irritate the nerve, either near to the muscle or far 

 from it, and he so arranged the experiment that 

 at the moment of opening the induction current, 

 the galvanometer circuit was closed, and was again 

 opened by the contraction of the muscle itself. The 

 interval, then, between the two swings of the needle 

 was that between the moment of irritating the nerve 

 and the moment of the muscular contraction. Ar- 

 rangements were then made for irritating the nerve 

 in two successive experiments first, close to the 

 muscle, and, second, at a distance of say two inches 

 from it. It was soon found that the muscle did not 

 respond at the instant the stimulus was applied to 

 the nerve, and that the further away the nerve was 

 irritated the later was the response. The first dis- 

 covery was that even when the nerve was irritated 

 close to the muscle, a period of something like the 

 y^j-th of a second always elapsed before the muscle 

 began to contract. In other words, the muscle did 

 not at once respond, but some time was occupied 

 in those molecular changes that precede contraction. 

 This period was termed by Helmholtz the period of 

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