1 84 A MANUAL OF PHYSIOLOGY 



way described under 2 (p. 177). Ligature the frsenum with a fine silk 

 thread, and use the thread to manipulate the heart. With a curved 

 needle pass a moistened silk thread between the aorta and the 

 superior vena cava, and tie it round the junction of the sinus and 

 right auricle (Fig. 74,). The auricles and ventricle stop beating as 

 soon as the ligature is tightened. The sinus venosus goes on beating. 

 Now separate the ventricle from the rest of the heart by an incision 

 through the auriculo-ventricular groove, or tie a second ligature in 

 the groove. The ventricle begins to beat again, the auricle remaining 

 quiescent in diastole (p. 151). Occasionally both auricle and 

 ventricle, or only the auricle, may begin to beat. 



u. Stimulation of Cardiac Sympathetic Fibres in the Frog. 

 (i) In the vago-sympathetic after the inhibitory fibres have been cut out 

 by atropine. -Arrange everything as in 7 (p. 182). Assure yourself, 

 by stimulating the vagus, that it inhibits the heart, and take a 



G 

 FIG. 8 1. ARRANGEMENT OF INDUCTION MACHINE FOR TETANUS. 



B, battery ; K, simple key ; P, primary coil ; S, secondary coil ; A, C, binding 

 screws to be connected with battery for single shocks ; F, G, binding screws for 

 tetanizing current ; N, Neef's hammer ; D, short-circuiting key in secondary ; 

 E, electrodes. D and E are drawn to a much larger scale than the rest of the 

 figure. 



tracing during stimulation. Then paint a dilute solution of atropine 

 on the sinus. Stimulation of the vagus, which is really the vago- 

 sympathetic (see Fig. 80), will now cause, not inhibition, but aug- 

 mentation (increase in rate or force, or both), since the endings of 

 the inhibitory fibres have been paralyzed by atropine. The strength 

 of the stimulating current required to bring out a typical augmentor 

 effect is greater than that needed to stimulate the inhibitory fibres. 

 Take a tracing to show augmentation produced by stimulating the 

 nerve. 



(2) By direct stimulation of the cervical sympathetic. Make the 

 same arrangements as in n (i), but, instead of isolating the vagus, 

 dissect out the sympathetic on one side in the manner described in 

 6 (2) (p. 181), and do not apply atropine to the heart. Lay the upper 

 (cephalic) end of the sympathetic on very fine and well-insulated 

 electrodes, and stimulate (Fig. 64, p. 151). (To insulate electrodes 

 the points may be covered with melted paraffin. When the paraffin 



