PHARMACOLOGY. 291 



(-) Can you devise an experiment that would positively 

 answer question " g." ? 



(2) Expose the vagus of dog "b" (see pp. 110-111). 

 Stimulate it with weak induced current, using shielded 

 electrodes. 



(0) What is the function of the cardiac fibers of the 



vagus? 

 (^) How, therefore, would you expect stimulation of 



the vagus to affect rate and rhythm of the heart 



beats ? 

 (<r) How would you expect severing of the vagus to 



affect the rate and rhythm of the heart beat ? 

 (//) How do you actually find the rate and rhythm of 



the heart beats affected by stimulation of the vagus? 



(3) Count the pulse, then give 5 mgrm. atropin hypo- 

 dermically. 



(a} Count the pulse at short intervals after the injec- 

 tion of atropin for at least 30 minutes, or until its 

 rate is markedly affected. 



(<) What is the effect of atropin on the rate of the 

 pulse ? 



(/) Could atropin produce this effect by acting on the 

 vagus center? On the vagus fibers ? On the vagus 

 terminations in the heart? On the heart muscle 

 direct ? 



(4) After the pulse rate has been markedly affected by 

 atropin stimulate vagus as before, using shielded 

 electrodes. 



(0) What is the effect on the rate of heart's action? 



() Compare this result with that obtained in experi- 

 ment (2). 



(<:} Had atropin acted solely by depressing the vagus 

 center would we have found a difference in results 



