HYDRASTINE AND CAFFK1NK 241 



What do you observe ? How do you account for this ? 

 Drop on some more of the drug and again stimulate the 

 nerve. Is there any change? Now take up the electrodes 

 and (while the drum is going) turn on a strong (tetaniz- 

 ing) current. With the extreme tips of the electrodes just 

 touch for a moment the tissues at the base of the heart 

 just where the sinus venosus joins the right auricle. 

 This is about the point where the inferior vena cava pass- 

 ing forward would bend up toward the right auricle. The 

 inferior (caudal) border of the tissue which forms the 

 connecting tube between the sinus venosus and the right 

 auricle is called the crescent. What result do you ob- 

 serve following a brief stimulation of this area? (Examine 

 Fig. 222.) 



EXPERIMENT XLI. 

 Hydrastine. (Turtle: Heart and Vagus Nerve.) 



1. Pith a turtle (brain and cord) and take a normal 

 heart tracing showing vagus inhibition in two or three 

 places. Lower the drum and start a second round of the 

 tracing. Drop some hydrastine solution (one cubic centi- 

 meter equals five milligrams) on the heart. Record the re- 

 sults and then stimulate the vagus nerve again. What do 

 you observe ? Apply more drug and stimulate again. Now 

 stimulate the crescent and note the results. What do you 

 observe? Can you explain this? 



EXPERIMENT XLIL 

 Caffeine. (Frog: Central Nervous System, Muscles.) 



1. Cut off the front part of the head of a frog (Fig. 

 220) and inject two cubic centimeters of caffeine solution 

 (the free drug, not a salt, is preferable use a saturated 

 solution in warm water) into the anterior lymph sac (Fig. 



