CHAPTER XXX. 



EXPERIMENTS TO DEMONSTRATE THE PUMPING 



ACTION OF THE HEART AND THE ACTION OF 



THE VALVES. 



Demonstration 6. A wide glass cannula is tied into the 

 superior vena cava of the excised heart of a dog or sheep and the 

 cannula connected by rubber tubing with a funnel. A glass tube 

 is also tied into the pulmonary artery, the upper end of the tube, at 

 a distance of about 50 cm. from the heart end, being bent double 

 and arranged so that the opening lies over the funnel which is 

 connected with the vena cava. The inferior vena cava is tied and 

 the preparation and tube are held by suitable clamps in a vertical 

 position ; water is poured into the funnel so that it distends the right 

 auricle and ventricle. Some of the water escapes through cut 

 vessels (left azygos vein) which are now tied. When the ventricle 

 is rhythmically compressed by the hand the water, which has mean- 

 while risen in the pulmonary tube to the level of the water in the 

 funnel, rises higher and higher with each compression, and remains 

 up between them, until it reaches the bend and flows back into the 

 funnel. This illustrates the circulation of the blood through the 

 heart. 



It is interesting to study the effect produced by DAMAGING THE 

 SEMILUNAR VALVE. The fluid still rises in the tube with each 

 compression, but leaks back into the ventricle between the "beats". 

 To raise the fluid in the tube high enough so that it overflows into 

 the funnel it is now necessary to compress the ventricle much more 

 rapidly. This illustrates in a rough way how the heart may com- 

 pensate for a valvular inefficiency by more energetic action. 



The OPERATION OF THE TRicusPiD VALVES is also readily shown 

 by removing the tube and cutting away most of the right auricle. 

 When the ventricle is filled the water flaps are floated up into 

 position, a narrow chink, however, remaining in the centre. This 

 can be temporarily closed by allowing the water to drop in the 



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