432 



ELECTRO-PHYSIOLOGY 



CHAP. 



proximal point ; this gives a rate of propagation of 6 '5 m. per 

 sec. (at 12 C.), or in another case 7'3 m. Schonlein has 

 recently given much higher values (1227 m.), and reckons 

 them in the same order as those of frogs' nerves. 



Marey's experiments seem to give a latent period of O'Ol" for 

 the discharge of Torpedo, i.e. the value originally given by von 

 Helmholtz for twitch in the frog's muscle. But as here, so in 

 the electrical organ it was subsequently found that if there is 

 any latent period of discharge in the sense that the causative 

 alterations in the substance of the plates are initiated later than 



Fir:. 272. p = twitch from the muscle, as marking moment of stimulation; c<7 = latent period of 

 muscle twitch discharged directly by an induction shock';~ef = latent period of twitch from the 

 organ discharge; t;< = latent period of electrical organ. 



the commencement of excitation (which from analogy with the 

 electrical phenomena of muscle is not very probable) such 

 latency must be much smaller than the original determination. 



Sachs, who experimented on Gymiwtus by a method corre- 

 sponding on the whole with Marey's, employed direct stimulation 

 with opening shocks, because it was found impossible to excite 

 organ-preparations from the nerve by single induction shocks. 

 He also adopted Pouillet's method of time-measurement. The 

 arrangement is according to Fig. 273. 



The strip of organ ( VH) lies between the clay shields of the 

 leading-in electrodes, from which wires lead to the double reverser 

 (D W). Other wires come from the uupolarisable electrodes 

 applied to the organ, that lead in the break shock from the 

 secondary coil (ft); the latter is discharged by Helmholtz's switch 



