434 ELECTRO- PHYSIOLOGY 



galvanometer circuit is accordingly longer than the latent period 

 of the shock. This may be calculated on du Bois-Eeymond's 



formula for the a-periodic magnet T = ^ ax . x, F being the 

 deflection from the constant current ; e, the basis of the natural 

 logarithms ; x, the effect due to current impact ; t m a x, the 

 duration of this or any other effect under the same conditions. 



Sachs accordingly gives a value of 0*00350", which ap- 

 proximately coincides with the latency of the muscle element 

 as given by Gad. Gotch determines it for Torpedo at 5 C., 

 as 0*012"-0*014"; at 20 C., on the other hand, it is only 0*005". 

 He invariably finds the latent period less in large specimens 

 than in small, and this cannot be altogether referred to the 

 greater intensity of discharge in the first case. Schdnlein, on 

 exciting Torpedo indirectly with descending constant currents, 

 found, with Bernstein's rheotome, a latent period of only 0*0002- 

 0*00025 sees. Since (as was said above) it cannot be sup- 

 posed that any appreciable time elapses in a plate of the electrical 

 organ, between the impact of a stimulus and the initiation of the 

 chemical process that underlies the electromotive action, the 

 apparent latency of the discharge in electrical organs must be 

 referred solely to the imperfection of experimental technique. 



The duration of discharge from the electrical organ seems, like 

 its latency, to be, generally speaking, of the same order of magni- 

 tude as that of the muscle twitch. Du Bois-Keymond pointed 

 this out as early as 1857 with the frog-interrupter. He led a 

 branch of the current discharged by Gymnotus into the nerve of 

 the frog's gastrocnemius muscle, which in twitching opened the 

 galvanometer circuit. With increased after-loading of the muscle 

 the initial deflections became steadily larger, while if the twitch did 

 away with a shunt to the galvanometer circuit the terminal de- 

 flections became smaller and smaller. " With sufficient loading a 

 point is reached at which in the first case the deflection of 

 the mirror due to the discharge shows no further increase, while in 

 the second, with unpolarisable (leading-off) saddles, there is only a 

 weak and inconstant remainder of the discharge." Marey sub- 

 sequently determined the period of the discharge of Torpedo (supra) 

 with the pendulum-myograph at about ^" . Sachs experimented 

 on Gymnotus by du Bois-Eeymond's method. His apparatus is 

 given in Fig. 274. 



. Leading-off saddles are applied to the fish in water, the current 



