80 LABORATORY MANUAL OF GENERAL PHYSIOLOGY 



Ligature." Moisten with Ringer a ligature thread and pass it under the 

 two aortae. Lift up the ventricle (turn it back) and tie the thread exactly 

 over the line marking the junction of the sinus and auricle. If the liga- 

 ture is not exactly placed, no change may occur. In that case tie another 

 thread at the same junction. Sometimes it takes 5 ligatures. What is 

 the change produced by the tying? (cf. Mitchell, "Gen. Physiol.," 1932, 

 p. 579). Compare with mammalian heart (cf. Wiggers, "Physiology in 

 Health and Disease," 1934, p. 445). This preparation is to be used in 

 Ex. 3. For a recent discussion of heart block cf. Gilson, Am. J. Physiol., 

 110: 376, 1935. Text 432, 434. 



3. The AU-or-None Effect in the Heart (Use a stationary drum). — 

 The beat of the auricle and ventricle are inhibited by a ligature (Ex. 2). 

 Fasten a straight fine wire (1 ft.) to one post of the secondary coil of the 

 inductorium. Make sure that it springs freely in a vertical direction. 

 Bend down about 3 ins. of the free end directly over the heart and bend a 

 fine hook at the tip which is to be inserted into the tip of the ventricle. 

 Now tie a thread on the wire at the bend and fasten the other end of the 

 thread to the heart lever. 



The following points must all be in the same vertical line directly 

 above the heart: attachment of thread on lever; attachment of thread on 

 wire; vertical arm of wire; attachment of hook to ventricle. Make 

 careful adjustments so that the heart has full mechanical advantage. 



THE HEART MUST BE DIRECTLY BENEATH ITS ATTACHMENT 

 TO LEVER. Tie another inductorium wire at ligature. 



Find a break shock that will cause the heart to contract. Record the 

 contraction. Turn the drum 2 mm., slide out the secondary coil 1 mm., 

 and after waiting 15 sees, stimulate again. Continue thus until the 

 heart fails to respond. 



Does the height of the contraction under these conditions vary with 

 the strength of the stimulus? Cf. Bowditch, Ber. d. k. sachs. Gessell. d. 

 Wiss., Leipzig, 1871, p. 682; Bayliss, p. 453; Barcroft, "Features in the 

 Architecture of Physiological Function," 1934, p. 250. Text p. 426. 



4. Treppe. — On a stationary drum record a series of contractions, at 

 2 sec. intervals, of a heart arranged as in Ex. 3, using break shocks of 

 constant strength (cf. Bayliss, p. 453; Mines, Jl. Physiol., 46: 1, 1913)- 

 Compare with treppe in a nerve net (cf. Pantin, Jl. Exp. Biol., 12: 389, 

 1935). Text p. 342. 



5. Changes of Irritability during a Single Cycle. — Arrange the heart 

 of a fresh frog as in Ex. 3 but without the ligature. Introduce the wires 

 only into, not through, the muscular wall of the heart; be careful to avoid 

 loss of blood. Let a signal, set as close as possible beneath the heart 

 lever, record the moment of stimulation. Start the drum at a rate which 

 results in a widely separated record of systole and diastole. Study the 



