200 PRACTICAL PHYSIOLOGY. [XXXV. 



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

 curve (fig. i2i). 



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. ii8). 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 imder each 

 (Lesson XXXV.). 



D. Remove the trac- 

 ■„ , o . • c- , . V o- , ^gs and varnish them. 



Fig 1 1 3— Fro? s Gastrocnemius Stimulated by a Single ° 

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



the primary and secondary coil being the same for both n Ttelatlon of 



shocks. In the lower figure the muscle was somewhat * « , / 



fatigued. Slow rate of speed. *' Lilt tO Strength 01 



Stimulus. — Suppose 

 one uses only break shocks, and, beginning with the first efi'ective 

 stimulus (" Minimal Contraction ") and gradually increasing the 

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

 of the " Hft " 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 appUed to the muscle 

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

 and the first eSective maximal stimulus is considerably greater than 

 by indirect stimulation {i.e., when the stimulus is apphed through 

 the nerve). 



LESSON XXXV. 



CRANK-MYOGRAPH— AUTOMATIC BREAK. 



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

 crank-myograph is used (fig. 1 1 9). The muscle placed on it can 

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

 saline. 



1. The Crank-Myogi'aph (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 tlie bell-crank rests (fig. 119, 



