ELEMENTARY EXPERIMENTAL PHYSIOLOGY 43 



Lesson IX. To be provided for each pair of Students. 

 1. Induction coil, keys, wires and pair of electrodes. 2. Bottle of 0'75 

 NaCl solution. 3. Strips of blotting paper. 4. Myograph stand and lever. 

 5. Drum. 6. Tuning fork beating 100 times per second with marking wire 

 attached. 7. Frog. 



FIG. 38. Single contraction of gastrocnemius in response to a maximal 

 make shock. 



Muscle loaded with lever and 30 grms. at axis of lever ; actual load on muscle, 6 grms. 

 Magnification, 5. Temp., 15 C. Time marker, 100 per sec. (A.P.B.) 



LESSON X 



G. INFLUENCE OF VARIOUS FACTORS UPON MUSCULAR 

 CONTRACTION 



Arrange an experiment in the same way as the last, and then 

 proceed as described in 1, 2, 3, 4 and 5. In each experiment mark 

 the point of stimulation. 



Each pair of students does one or more of the following experiments, 

 and then compares their tracings with those of others doing the other 

 experiments. 



1. The Effect of the Length of the Muscle on the Contraction and Work 

 Done. 



A. With the screw-pin below the lever well depressed, attach a 

 weight to the lever such that the muscle in contracting raises it to 

 near the maximum (about 10 grms.), and with the muscle thus 

 lengthened by the weight record a contraction. 



B. Now screw up the pin below the lever so as just to prevent the 

 weight stretching the muscle. Adjust the level of the drum so 

 that the lever marks on the same base line as before, and again 

 take a trace over the last on the drum. 



Mark the moment of stimulation, etc., as before. Fix and 

 compare the two traces, and work out the extent of contraction 

 and the work done in each. 



2. Influence of Load. 



1. On the course of Contraction. METHOD. (1) Take a trace of a 

 muscle twitch in the usual way but with no weight on the lever. 



