98 SPECIAL PHYSIOLOGY 



Stimulation of the cardiac sympathetic distinctly increases the 

 pulse rate. 



Find the corresponding nerve of the opposite side, verifying your 

 choice by observing the effect of stimulation. 



Cut both cardiac sympathetic nerves and observe the rate of the 

 heart beat at intervals of five minutes through a period of thirty 

 minutes. 



XI. THE INFLUENCE OF THE VAGUS AND THE CARDIAC 

 SYMPATHETIC UPON THE ARTERIAL BLOOD PRESSURE. 



1. Appliances. Dog or large rabbit; animal holder; mercury 

 manometer, with float or tambour and with flushing flask of non- 

 coagulant; with tubing and cannulse, as described in Appendix A, 

 12; a kymograph, inductorium ; Daniell cell; two Du Bois-Reymond 

 keys; operating case;, chloroform, ether, morphine; hypodermic 

 syringe. 



2. Preparation. Let eight students in four groups of two each 

 have charge of (a) anaesthesia, (6) operations, (c) electric apparatus 

 and stimulation, (d) pressure tracings. 



3. Operations, (a) Anesthetize the animal in accordance with 

 directions given in previous exercises for the dog and rabbit, respec- 

 tively. 



(6) Remove the hair from the throat; make a cutaneous incision 

 in the median ventral line from the anterior end of the sternum to 

 the anterior end of the larynx. Remove the subcutaneous tissue 

 and expose the sternomastoid and sternothyroid muscles. Let one 

 operator expose the carotid artery of one side while the other operator 

 exposes the vagus and sympathetic of the other side. 



(c) Adjust the shielded electrode for stimulation. Insert the 

 cannula into the artery. 



(d) Make the tracing of arterial blood pressure in accordance with 

 directions given in a previous exercise. 



While the tracing is in progress stimulate the vagus with a moderate 

 tetanizing current for a period of two to five seconds. Repeat the 

 stimulation at intervals of ten to twenty seconds for ten minutes. 



Adjust the electrode for stimulation of the cardiac sympathetic. 

 Stimulate. 



4. Observations. (1) What is the average blood pressure meas- 

 ured in centimetres of mercury in the animal under observation 

 before stimulation of a nerve? 



(2) What influence does stimulation of a vagus nerve have upon 

 the arterial blood pressure? 



(3) Is the effect clearly marked on the pressure tracing? 



(4) What influence does stimulation of the cardiac sympathetic 

 have upon arterial blood pressure? 



