48 LABORATORY MANUAL OF GENERAL PHYSIOLOGY 



8. Sununation of Stimuli. — Send in two shocks in rapid succession by 

 making and quickly breaking, so as to obtain a curve showing what 

 happens when a muscle is stimulated at the height of contraction. If 

 you fail in obtaining the correct time interval between shocks the first 

 time, try again. No time record is required. Text p. 295. 



9. Incomplete Tetanus. — Repeat, making and breaking by hand in 

 rapid succession. Summation of several shocks should be obtained, 

 giving an incomplete tetanus. No tuning fork. 



10. Complete Tetanus. — Describe a curve of contraction with tetaniz- 

 ing current, i.e., with interrupted faradic or induced current. Do not 

 stimulate for longer than 3 seconds. No tuning fork. Cf. Nicolai, 

 Pfliiger's Arch. 237: 399, 1936. Text p. 295. 



11. Isometric Contraction. — Record twitch (weak shock) with the 

 isometric lever (supplied by instructor). Superimpose the curve on a 

 calibration line made when a ten gram weight is placed at the point of 

 attachment on the lever. No tuning fork. Cf. Wiggers, "Physiology," 

 1st Ed., p. 8, 1934. 



12. Fatigue Curve. — With very slow speed of drum, fatigue the muscle 

 by prolonged tetanus. Note the gradual relaxation in spite of continued 

 stimulation. When completely fatigued, allow to rest. Wash with 

 Ringer solution. Then take curves of single twitches with maximal break 

 shocks. Compare with the curves from the fresh muscle. No tuning 

 fork. Cf. Simonson, Ergebnisse Physiol., 37: 299, 1935. 



13. Influence of Circulation on Fatigue. — Anaesthetize a frog with 

 urethane (1 cc. of 10% sol. to 50 grams of frog injected into dorsal lymph 

 sac), and place dorsum down on frog board. Make small incisions in 

 the skin of the ankle and free the Achilles' tendons. Avoid hemorrhage. 

 Tie threads to tendons and attach one to a muscle lever weighted with 

 20 grams. Insert fine wire electrodes through skin into gastrocnemius 

 by means of needles threaded on the fine wire. Pass a linen ligature 

 about the thigh and tie off circulation. For connection to lever, pass 

 thread over a pulley consisting of a spool rotating on a rod. Stimulate 

 at once with a maximal tetanizing current to obtain a fatigue curve. 

 Now obtain a curve from the other leg. Study the effect of rest in each 

 case. 



14. Fatigue of Himian Muscle. — Clamp the L-shaped ergograph to 

 the table. Allow the adjustable rod to rest on the index finger and 

 record a fatigue curve on the kymograph. 



15. Artificial Tetanus of Human Muscle. — With hand in ergograph as 

 above place on the forearm a flat metal electrode covered with cotton wet 

 with salt solution (indifferent electrode). With a metal rod electrode 

 similarly covered with moist cotton touch the skin over the abductor of 

 the index finger near the angle between the first and second metacarpals. 



