THE ACTION OF THE VALVES. 229 



impulse from the auricles to the ventricle is " blocked" to a 

 greater or less extent, when the auricles will contract more 

 frequently than the ventricle. 



LESSON LI I. 



THE VALVES OF THE HEART-STETHO- 

 SCOPE-CARDIOGRAPH MEIOCARDIA 

 AND AUXOCARDIA REFLEX INHI- 

 BITION OF THE HEART. 



1. The Action of the Valves in the Dead Mammalian Heart. 

 This is of value in order that the student may obtain a know- 

 ledge of the mechanical action of the valves. The heart and 

 lungs of a sheep with the pericardium still unopened must be 

 procured from the butcher. 



(a.) Open the pericardium, observe its reflection round 

 the blood-vessels at the base of the heart. Cut off the lungs 

 moderately wide from the heart. Under a tap wash out any 

 clots in the heart by a stream of water entering through 

 both auricles. Prepare from a piece of glass tubing, 15 mm. 

 in diameter, a short tube, 8 cm. in length, with a flange on 

 one end of it, and another about 60 cm. long. Fix a ring to 

 hold a large funnel on a retort stand. 



(6.) Tie the short tube into the superior vena cava, the 

 flanged end being inserted into the vessel. It must be tied 

 in with well-waxed stout twine. In the pulmonary artery 

 (P. A. ) separated from its connections with the aorta which lies 

 behind it tie the long tube, the flange securing it completely. 

 Ligature the inferior vena cava, and the left azygos vein 

 opening into the right auricle. Connect the short tube by 

 means of india-rubber tubing with the reservoir or funnel in 

 the retort stand. Keep the level of the water in the funnel 

 below the upper surface of the P. A. tube. Fill the funnel 



