284 PRACTICAL PHYSIOLOGY. [LX. 



('O]. the cannula used being one fixed in the glass stopper of the bell-jar, and 

 attach the inlet tube of the cannula to the reservoir of nutrient fluid, while 

 the outlet tube is arranged so as to allow fluid which has passed through the 

 heart to drop into a suitable vessel. 



(c.) Introduce the cannula, with the heart attached, into the oil, and see 

 that the stopper is securely fixed. Open the stopcock (e), and allow some oil 

 to flow out of o, thus rendering the pressure within sub-atmospheric ; and as 

 soon as the pressure has fallen sufficiently, and the little piston is gradually 

 drawn up to the proper height, close the stopcock. Attach the needle of the 

 piston to the recording light lever, and take a tracing. 



LESSON LX. 



HEART-VALVES ILLUMINATED HEART STETHO- 

 SCOPE CARDIOGRAPH POLYGRAPH - MEIO- 

 CARDIA REFLEX INHIBITION OP THE 

 HEART. 



1. Action of Heart- Valves. This is of value in order that the 

 student may obtain a knowledge 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 : reflexion 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. 



(b.) 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 with water ; it distends the right auricle, passes into 

 the right ventricle, and rises to the same height in the P.A. tube 

 as the level of the fluid in the funnel. Compress the right ventricle 

 with the hand ; the fluid rises in th$ P.A. tube ; arid observe on 

 relaxing the pressure that the fluid remains stationary in the P.A. 

 tube as it is supported by the closed semilunar valves. If the right 



