214 



ELECTRO-PHYSIOLOGY 



CHAP. 



with non-polarisable, movable electrodes, stood in front of a ver- 

 tical cylinder, which turned upon a crank, and the contractions of 

 both halves of the muscle were recorded on its smoked surface, 

 so that the point of the tuning-fork lever lay vertical to the two 

 muscle levers, which move (up and down) in opposite directions ; 

 in this way it is possible, independent of the rate at which the 

 cylinder rotates, to measure the difference in time between 

 the beginning of the two twitches as well as the period of 

 latent excitation, if the experiment is arranged so that the tuning- 

 fork begins to vibrate at the precise moment of closure or opening 

 of the current, as may easily- be effected by withdrawing a con- 

 ducting wedge introduced 

 between the limbs of the 

 fork (Fig. 86). 



By this method two 

 curves of twitch are ob- 

 tained with the closure 

 of a battery current of 

 sufficient intensity, one 

 traced upwards and the 

 other downwards, which 

 are always in such rela- 

 tions with each other that 

 the curve corresponding 

 with the kathodic half 

 of the muscle rises per- 

 ceptibly earlier from 

 the abscissa than the other (Fig. 87, a, b). 



If a perpendicular is drawn from each abscissa at the point at 

 which the curve commences, the number of tuning-fork vibrations 

 enclosed between the two perpendiculars gives the rapidity at 

 which the wave of contraction, measured from its point of origin 

 at the kathode to the first muscle section beyond the fixed spot, 

 is transmitted. The length of this tract is 20-27 mm. according 

 to the size of the frog; this corresponds with 46 vibrations 

 of the tuning-fork, and the velocity of the make excitation is 

 therefore 12 m. per sec. 



The same method may be employed to investigate the 

 time -relations of the break excitation. Since the denervated 

 muscle reacts more slowly to the break stimulus, the intensity of 



FIG. 86. Registering tuning-fork, for interruption 

 or closure of current. (Bering.) 



