ACTION OF THE VALYES. 201 



through the auriculo-ventricular opening, the valves are 

 floated up, and finally closed when the ventricle is completely 

 filled. This experiment we have repeated and found to be 

 correct ; but in this way we are far from fulfilling the natu- 

 ral conditions of the circulation. In the natural action of the 

 heart, the blood flows from the auricles in a large stream, 

 which opens the valves and applies them to the walls of the 

 ventricles. This is quite different from the action of a small 

 stream, which may insinuate itself between the lips of the 

 valves, and force them up by reacting from the ventricle. If 

 the semilunar valves be exposed, and the artery closed, a 

 stream of water poured from the ventricles will close the 

 valves ; and yet we could hardly say that in the natural course 

 of the circulation the valves at the arterial orifices are closed 

 by the ventricular systole. 



These experiments do not throw any doubt upon the fact 

 that the auriculo-ventricular valves are closed by the pressure 

 of blood against them during the ventricular systole. 



If a bullock's heart be prepared by cutting away the auri- 

 cles so as to expose the mitral and tricuspid valves, securing 

 the nozzles of a double syringe in the pulmonary artery and 

 aorta, after having destroyed the semilunar valves, and if 

 fluid be injected simultaneously into both ventricles, the play 

 of the valves will be exhibited. The mitral valve effectually 

 prevents the passage of the fluid, its edges being so accurately 

 approximated that not a drop passes between them ; but when 

 the pressure is considerable, a certain quantity of fluid passes 

 the tricuspid valve. There is, indeed, a certain amount of 

 insufficiency at the right auriculo-ventricular orifice, which 

 does not exist on the opposite side. 



This fact was first pointed out by Mr. T. King, 1 and is called 

 by him the " safety-valve function of the Tight ventricle" 

 The advantage of this slight insufficiency is apparent on a 

 little reflection. The right ventricle sends its blood to the 



1 KING, An Essay on the Safety-valve Functions of the Right Ventricle of the 

 Human Heart. Guy's Hospital Keports, 1837, vol. ii. p. 104. 



