PRACTICAL EXERCISES 



205 



(b) Take two wide glass tubes, drawn slightly into a neck at one end. 

 One of the tubes should be about 10 cm. long, and the other about 

 50 cm. Tie the short tube A firmly by its neck into the superior vena 

 cava, the long tube B into the pulmonary artery. Ligature the inferior 

 vena cava. Connect A by a small piece of rubber tubing with a funnel 

 supported in a ring on a stand. Pour water into the funnel till the 

 right side of the heart is full. It will escape from the left azygos vein, 

 which must be tied. Put on any additional ligatures that may be 

 needed to render the heart water-tight. Support B in the vertical 

 position by a clamp. Fill the funnel with water, and it will rise in B 

 to the same level as in the funnel. Now compress the right ventricle 

 with the hand, and the water will rise higher in B. Relax the pressure 

 and notice that the water remains at the higher level in B, being pre- 

 vented by the semilunar valves from flowing back into the ventricle. 

 By alternately compressing the ventricle and allowing it to relax, water 

 can be pumped into B till it escapes from its upper end, and if this is 

 so curved that the water falls into the funnel, a ' circulation ' which 

 imitates that of the blood can be established. Note that during the 

 pumping the sinuses of Valsalva, behind the semilunar valves at the 

 origin of the pulmonary artery, become prominent. 



(c) Take out B and tear out one of the segments of the semilunar 

 valve. Replace B, and notice that, while compression of the ventricle 

 has the same effect as before, the water no longer keeps its level on 

 relaxation, but regurgitates into the ventricle. This illustrates the 

 condition known as insufficiency or incompetence of the valves. But 

 if the injury is not too extensive, it is still possible, by more vigorously 

 and more rapidly compressing the heart, to pump water into the funnel. 

 This illustrates the establishment of compensation in cases of valvular 

 lesion. 



(d) Now remove both tubes. Tie the pulmonary artery. Cut away 

 the greater part of the right auricle. Pour water into the auriculo- 

 ventricular orifice, and notice that the segments of the tricuspid valve 

 are floated up so as to close the orifice. Invert the heart, and the 

 ventricle will remain full of water. Open the right ventricle carefully, 

 and study the papillary muscles and the chordae tendineae, noting that 

 the latter are inserted into the lower surface of the segments of the 

 tricuspid valve, as well as into their free edges. 



(e) Repeat (b), (c), and (d) on the left side of the heart, tying tube B 

 into the aorta as far from the heart as possible, and A into the left auricle. 



(/) Separate the aorta from the left ventricle, cutting wide of its 

 origin so as not to injure the semilunar valves, and tie a short wide 

 tube into its distal end. Fill the tube with water, and notice that the 

 valves support it. Cut open the aorta just between two adjacent segments 

 of the valve, and notice the pockets behind the segments, and how they 

 are related to each other, and connected to the wall of the vessel. 



1 6. Sounds of the Heart. (a) In a fellow-student notice the position 

 of the cardiac impulse, the chest being well exposed. Use both a 

 binaural and a single-tube stethoscope. Place the chest-piece of the 

 stethoscope over the impulse, and make out the two sounds and the 

 pause, (b) With the hand over the radial or brachial artery, try to 

 determine whether the beat of the pulse is felt in the period of the 

 sounds or of the pause, (c) Listen with the stethoscope over the 

 junction of the second right costal cartilage with the sternum, and 

 compare the relative intensity of the two sounds as heard here with 

 their relative intensity as heard over the cardiac impulse. 



17. Cardiogram. Smoke a drum, and arrange a recording tambour 

 and a time-marker beating half or quarter seconds to write on it (Fig. 88, 



