174 



A MANUAL OF PHYSIOLOGY 



a bichromate, or a Leclanche cell in the primary circuit, which 

 should also include a simple key. Insert a short-circuiting key 

 in the secondary circuit. Attach the electrodes to the short-cir- 

 cuiting key, push the secondary coil up towards the primary until the 

 shocks are distinctly felt on the tongue when the Neef s hammer is 

 set going and the short-circuiting key opened. Pith the brain of a 

 frog, expose the heart, dissect out the vagus on one side, ligature it 

 as high up as possible, and divide above the ligature. Fasten the 

 electrodes on the cork plate by means of an indiarubber band, and 



lay the vagus on them. 

 Set the drum off (at slow 

 speed). After a dozen 

 heart-beats have been re- 

 corded, stimulate the vagus 

 for two or three seconds by 

 opening the short-circuiting 

 key. If the nerve is active, 

 the heart will be slowed, 

 weakened, or stopped. In 

 the last case the lever will 

 trace an unbroken straight 

 line ; but even if the stimu- 

 lation is continued the 

 beats will again begin. 



8. Stimulation of the 

 Junction of the Sinus and 

 Auricles. After a suf- 

 ficient number of the obser- 

 vations described in 7 have 

 been taken with varying 

 time and strength of stimu- 

 lation, take the writing- 

 points off the drum, apply 

 the electrodes directly to 

 the crescent at the junction 

 of the sinus venosus with 

 the right auricle, and 

 stimulate. The heart will 



FIG. 64. RELATION OF THE SYMPATHETIC 

 TO THE VAGUS IN THE FkOG. 



i, 2, 3, 4 are spinal nerves. be a ff ec ted very much in 



the same way as by stimula- 

 tion of the vagus, except that during the actual stimulation its beats 

 may be quickened and the inhibition may only begin after the 

 electrodes have been removed (Fig. 46, p. 13;,). 



9. Effect of Muscarine and Atropia. Paint on the sinus venosus 

 with a small camel's-hair brush a very dilute solution of muscarine. 

 The heart will soon be seen to beat more slowly, and will ultimately 

 stop in diastole. Now apply a dilute solution of sulphate of atropia 

 to the sinus. The heart will again begin to beat. Stimulation of 

 the vagus will now cause no inhibition of the heart, because its 

 endings have been paralyzed by atropia. (Muscarine has also been 



