MUSCLE AND NERVE 37 



lever may record down-strokes. Record the zero line or abscissa. Put 

 ten weights of 10 grams each successively into the scale pan, recording 

 each time the extension which the muscle suffers. Carefully remove the 

 weights one by one, allowing the muscle to register its curve of deten- 

 tion. Does the lever return to the abscissa? 



Obtain a curve of elasticity from a rubber band under similar con- 

 ditions. Compare the results. Adjust the stimulating electrodes upon 

 the upper part of the muscle. Obtain a curve of elasticity from this 

 muscle while it is being stimulated with a tetanic current of moderate 

 strength. What differences do you detect between this curve and that 

 obtained under ordinary conditions? Explain. 



FIG. 15. EXTENSIBILITY AND ELASTICITY. 



A, Rubber band, and B, gastrocnemius muscle of frog successively loaded with 10- 

 gram weights. The second curve shows a decreasing extension for equal increments, 

 hence, the line joining the ends of the ordinates is curved. 



Annotation. A rubber band is perfectly elastic, i. e., it recoils until its abscissa 

 has been reached, provided it has not been extended unduly. The same holds true 

 of muscles in situ; in fact, they are well protected against all excessive degrees of 

 extension. Outside the body muscles are imperfectly elastic. After their con- 

 stituent fibers have been stretched they cannot resume their original shape. A 

 fatigued muscle (tetanized) can be extended much more easily and recoils with much 

 greater difficulty. 



4. Measurement of Muscular Power. Prepare a gastrocnemius 

 muscle of a recently killed frog and fasten the femur in the clamp. 

 Connect its tendon with the writing lever. Adjust the after-loading 

 mechanism so that the lever remains horizontal. Attach weights of 

 100 grams each to the lever until the muscle is no longer able to lift 

 them when stimulated with a tetanic current of moderate strength and 

 brief duration. Determine the maximal load lifted and also the weight 

 of the muscle. Compute the power per gram of muscle substance. 



5. Comparison Between Compact and Long Muscles. Prepare the 

 sartorius muscle of the opposite leg of the same frog. It is situated upon 

 the inner aspect of the thigh and extends between the ilium and the 

 tibia. Raise its tendon at the tibia and tie a fine silk thread around it. 

 Separate the entire muscle from the fascia connecting it with other 

 muscles and cut its other end, leaving the ilium attached. Determine 

 the maximal load which this muscle is capable of lifting under condi- 

 tions identical with those just described. Which muscle develops 



