46 LABORATORY MANUAL OF GENERAL PHYSIOLOGY 



(b) Action of Distilled Water. — Remove a sartorius muscle (Fig. 3) 

 from a frog as follows. Seize the sartorius tendon (ventral aspect of leg) 

 at the tibial insertion (knee). Lift the free end and separate the muscle up 

 to the origin by snipping the fascia on each side. Sever at origin and 

 suspend half-immersed in distilled water. Observe for 10 mins: move- 

 ments; change in volume or color. Cf. Baldwin, "Comp. Biochem.," 

 1937, p. 17. 



(c) Hypertonic Saline. — Immerse another sartorius muscle in 20% 

 NaCl and observe for ten minutes. Note any effects. 



5. Galvani's Experiment. — Prepare a sciatic gastrocnemius preparation 

 for obtaining records (stationary or moving drum). Hold in contact a 

 short zinc strip and a short bent copper wire. Touch the free ends of the 

 metals to the nerve. Explain result. If possible obtain a record. Cf. 

 Fulton and Gushing, Annals of Science, 1: 239, 1936. Text p. 295. 



6. Electromotive Phenomena in Muscle (Rheoscopic Frog). — Make 

 two nerve-muscle preparations designated A and B. Lay nerve of A 

 lengthwise along muscle of B. Stimulate the nerve of B as far as possible 

 from the muscle, with a submaximal induction shock. Result? Stimulate 

 with interrupted current. Prove that the "secondary contraction" is not 

 due to escape of current. The nerve may be placed on a vigorously 

 beating heart. Cf. Lillie, Am. Joum. Physiol., 34: 414, 1914; Lillie, 

 "Protoplasmic Action," 1932, p. 392. 



7. The Curve of Muscle Contraction. — (Nerve not required for this 

 experiment.) 



Mount a gastrocnemius preparation without the nerve on the muscle 

 lever and load it with a ten-gram weight. Connect the ends of the muscle 

 to the poles of the secondary coil of an inductorium by fine copper wires. 

 Put a signal magnet and a simple key in the primary circuit. Arrange a 

 writing point on a tuning fork to record hundredths of a second. Bring 

 the three writing points into the same vertical line, and as close together 

 as possible. All levers should be tangents to the drum. It will be most 

 convenient to have the muscle lever above and the tuning fork and signal 

 below. Set tuning fork in vibration. Avoid superimposing time records. 



Spin the drum rapidly by hand, and record the curve obtained from a 

 maximal shock. Stop the drum, remove the tuning fork, but carefully 

 avoid disturbance of the relative position of the other two points. The 

 tuning fork must be allowed to mark only during the revolution in which 

 the curve is actually made. Turn the drum cautiously until the signal is 

 exactly at the point where the shock was given and mark the correspond- 

 ing position of the muscle lever (simultaneous coordinates). Calculate 

 in fractions of a second (1) the latent period, (2) the period of shortening, 

 (3) the period of relaxation. Make several determinations. The nature 

 of the latent period is described by Snyder, Am. J. Physiol., 115: 441, 1936. 

 Text p. 294. 



