88 LABORATORY MANUAL OF GENERAL PHYSIOLOGY 



draw off fluid in pericardium and determine volume. What is the func- 

 tion of pericardium? (cf. Howell, 12th Ed., p. 575; Skramlik, Zeit. 

 vergl. Physiol., 15: 550, 1931). 



14. Inhibition by Vagus Stimulation. — Expose the vagus nerves at the 

 base of the neck and place silk ligatures loosely about them. The liga- 

 tures will be tied later. Arrange an induction coil for tetanizing currents 

 of moderate strength, and, using the briefest possible periods of stimula- 

 tion, make sure by physiological test that the nerves isolated are the 

 vagi. 



(a) Describe the appearance of the heart during vagal stimulation. 

 Attach one heart lever by a thread to tips of the auricles (thread with 



needle). Attach a second lever to the tip of ventricle. Arrange two heart 

 levers to write on a smoked drum; set the writing points in the same verti- 

 cal line, and directly beneath them place an electro-magnetic signal. 

 Counter weight levers with plasticine so that the chambers hang 

 vertically. 



(b) While recording simultaneously the contractions of the auricles 

 and ventricle, carry out the following procedures. Be sure to leave a 

 sufficient interval of time after each step to permit a return to the former 

 state. 



Stimulate the left vagus. 



Stimulate the right vagus. 



Tie the ligature on the left vagus. 



Tie the ligature on the right vagus. 



Apply prolonged stimulation to the right vagus peripheral to the 

 ligature. 



Describe the results in detail (cf. Bayliss, p. 683). 



Distinguish between inotropic and chronotropic effects. 



Allow the heart to trace its recovery after inhibition. 



The action of the vagus was discovered by Lower, 1669, Tractatus de 

 Corde, London. He ligated the nerve and thought that he had blocked 

 the flow of "spirits" to the heart (cf. Haldane and Priestly, "Respira- 

 tion," p. 2). The effect of stimulating the vagus was studied by the 

 Weber brothers in 1845 (cf. Bayliss, p. 683). Text p. 437. 



15. Cardiac Tonus and Salt Effects. — While the heart is still in place, 

 cut the two auricles, with the sinus attached, away from the ventricle. 

 Leave in place the ligatures about the tips of the auricles, attaching one to 

 an L-shaped glass rod, the other to a heart lever. Slit open the auricles 

 with scissors to permit diffusion of salts. Set the glass rod and the 

 auricular muscle in a beaker containing 250 cc. of Ringer with oxygen. 

 Let the drum turn at a speed which just fails to cause a fusion of the records 

 of the contractions. Replace the Ringer with 0.75% NaCl plus 0.01% 

 NaHCOs (buffer) and make a continuous record. Note that after a time 



