106 



THE PHYSIOLOGY OF MUSCLE AND NERVE. 



by Bernstein to precede the wave of contraction in muscle; that 

 is, in a stimulated muscle fiber the electrical change at any point 

 precedes the mechanical process of shortening. This relation- 

 ship is shown in the accompanying illustration (Fig. 48), in which 

 the mechanical contraction (movement of the lever) is photo- 

 graphed simultaneously with the movement of the string of the 

 string-galvanometer which indicates the electrical change. As 

 the figure shows the electrical change is diphasic, owing to the op- 

 posite effects on the galvanometer of the change of potential at 







Fig. 48. Simultaneous record of the mechanical and electrical change in a contracting 

 muscle: 1, Mechanical curve of contraction, photograph of the lever; 2, movement of the 

 string of the string-galvanometer (owing to its faintness it was necessary to retouch this 

 curve) ; movement upward indicates an increase of negative potential at the upper end of the 

 muscle; 3, time record in hundredths of a second; 4, the stimulating lever; the break in the 

 line indicates the moment of stimulation; on the curve of contraction (1) this moment is 

 indicated by x; on the curve showing the movement of the string (2) the same instant is 

 marked by the small nick in the curve preceding the large wave caused by the electrical 

 change. The curve was obtained from the gastrocnemius muscle of a frog, stimulated 

 through its nerve by a single induction shock, contraction isotonic. The leading-off electrodes 

 were placed at the ends of the muscle; galvanometer string under tension. The electric curve 

 is diphasic, and both phases are completed within the latent period of contraction (Snyder). 



the two points lead off to the galvanometer, but the first phase, 

 which begins almost immediately on stimulation, is completed 

 before the muscle begins to shorten. We may suppose that 

 the electrical change is an indication of the excitation, or pos- 

 sibly constitutes the excitation that sets up the chemical change 

 of contraction, or else that the change in electrical potential 

 is caused by the chemical change of contraction and precedes 

 the mechanical result of shortening, since the latter process 

 will have a certain latent period. It has been shown, indeed, 

 by Demoor that a completely fatigued muscle may still con- 

 duct an excitation (muscle impulse), although unable to con- 

 tract, and the same fact has been demonstrated by Engelmann 



