LABORATORY MANUAL OF PHYSIOLOGY. 



Explain the difference in the effect of strong and weak stimu- 

 lation. 



(d) Effect of Stimulating Vagus Terminals. Using the same 

 heart, stimulate behind, between the auricles and the sinus veno- 

 sus. Compare these results with those of (a), (6), and (c). 



VII. REFLEX INHIBITION OF THE FROG'S HEART. 



Prepare a fresh frog. Do not pith, but anaesthetize, lightly, with 

 ether. Expose one sciatic nerve as well as the heart. No tracing 

 need be made. The beat may be studied by direct observation. 



(a) Count the number of beats in ten seconds; in one minute. 

 With a scalpel handle, gently tap the abdomen in the stomach re- 

 gion for five seconds. During and after the tapping, observe and 

 count the number of heart-beats. What is the effect of the tapping 

 upon the beat of the heart ? Is it accelerated or inhibited ? 



(ft) Introduce into the stomach, by way of the mouth and 

 oesophagus, a pair of shielded electrodes. In this way stimulate 

 the stomach with a medium strong current and note results in rela- 

 tion to the heart-beat. 



(c) Cut the sciatic nerve. Is there any effect upon the heart- 

 beat ? Stimulate its central end with a medium strong current. 

 What is the effect upon the heart-beat ? 



(d) Cut both vagus nerves. Can reflex inhibition now be ob- 

 tained ? 



VIII. EFFECT OF DRUGS. 



^ 1. Atropine. Pith a frog. Expose the heart and vago-sym- 

 pathetic nerve. Place a pair of small electrodes under the nerve 

 and connect these with the inductorium arranged for medium 

 strong tetanizing current. Connect the ventricle with the heart 

 lever for recording on a medium fast drum. Take a normal trac- 

 ing, before and after bathing the heart with physiological salt so- 

 lution. Take a time tracing for comparison. Stimulate the nerve 

 with the tetanizing current for several seconds. There should be 

 inhibition of the heart-beat. 



Wait until the after-effects of the nerve stimulation have disap- 



