200 PRACTICAL PHYSIOLOGY. [XXXV. 



(/;.) Study the muscle-curve obtained, a so-called " isotonic " 

 curve (fig. 121). . . 



C. Vary the velocity of the cylinder, and observe how the 

 form of the curve varies with the variation in velocity of the 

 cylinder (fig. 118). Use only the break shock, and record the 



contractions either (i.) 

 all on one abscissa, or 

 (ii.) record each con- 

 traction on a different 

 abscissa, recording a 

 time-curve under each 

 (Lesson XXXV.)- 



D. Remove the trac- 

 ings and varnish them. 



FlG. 118 Frogs Gastrocnemms Stimulated by a Single 

 Make (M.) and Break (B.) Shock, the distance between 



the primary and secondary coil being the same for both Q Relation of 

 shocks. In the lower figure the muscle was somewhat _ ' ,, 

 fatigued. Slow rate of speed. " Lift " to Strength Of 



Stimulus. Suppose 



one uses only break shocks, and, beginning with the first effective 

 stimulus ("Minimal Contraction") and gradually increasing the 

 strength of the stimulus, one obtains a gradual increase in the height 

 of the " lift " until a certain maximum of lift (" Maximal Con- 

 traction ") is reached, above which, even though the stimulus be in- 

 creased, there is no further shortening of the muscle. If a muscle 

 be stimulated directly (i.e., the electrodes applied to the muscle 

 direct), the difference between the first effective stimulus (minimal) 

 and the first effective maximal stimulus is considerably greater than 

 by indirect stimulation (i.e., when the stimulus is applied through 

 the nerve). 



LESSON XXXV. 

 CRANK-MYOGRAPH AUTOMATIC BREAK. 



Instead of the muscle-lever shown in fig. 1 16, very frequently the 

 crank- my ograph is used (fig. 119). The muscle placed on it can 

 be kept moist by a cover of blotting-paper moistened with normal 

 saline. 



1. The Crank-Myograph (fig. 119) is fixed on a suitable sup- 

 port, so that it can be adjusted to any height desired. 



After-Load. In the crank-myograph, under the lever, is a 

 screw on which the horizontal arm of the bell-crank rests (fig. 119, 



