HEART PREPARATION. 225 



centre of the chink; following each drop the flaps come accurately 

 together because the waves of pressure produced by each drop 

 are reflected onto the under surface of the flaps from the walls of the 

 ventricle. What significance may this observation have in con- 

 nection with the mechanism of the closure of the valves in the 

 normal heart? 



To illustrate the efficiency of the tricuspid valves, ligate the 

 pulmonary artery, fill the ventricle with water, and hold the ven- 

 tricle upside down; the water stays in. 



The operation of the valves can be very clearly shown by ob- 

 serving them through windows inserted in the right auricle and 

 pulmonary artery. This is known as GAD'S HEART PREPARA- 

 TION. 



Demonstration 7. The general arrangement, using an ox 

 heart, is shown in Fig. 66. A brass tube A (40 cm. diam.) 

 closed by a glass window at one end and with a narrow tube soldered 

 into its side is tied into the right auricle, and another similar, but 

 narrower tube B (25 cm. diam.) into the pulmonary artery. The 

 side tube of A is connected by rubber tubing with the outflow of 

 an irrigation bottle, to the mouth of which leads a tube from B. 

 Through a narrow cut in the apex of the ventricle a brass tube 

 C connected at its free end with a rubber bulb and having a side 

 tube closed by a small rubber stopper, which is pierced by water- 

 proofed insulated wires, is inserted and tied in. The wires are 

 connected with a small electric lamp D which projects into the 

 ventricle. By rhythmically compressing the bulb E, to simulate 

 the ventricular contractions, water is transferred from the auricle 

 to the pulmonary artery, and with each pulsation the tricuspid 

 and semilunar valves can be very distinctly seen to open and 

 close in obeyance to the pressure changes. 



