THE MECHANISM OF THE CIRCULATION. 



Fig. 2. — Diagram showing 

 the resultant pull of 

 the papillary muscles. — 

 Ludwig. 



The Valves of the Heart and the Action of the 

 Papillary Muscles. 



The auriculo-ventricular valves. — If the auricles be removed from 

 the freshly excised heart of a mammal, and the rest of the organ be 

 gently placed under water, these valves immediately float upwards and 

 almost close the auriculo-ventricular orifices. This is not due to the 



specific gravity of the valves, for an excised valve 

 placed in water slowly sinks. The closure of the 

 valves is caused by eddies. In its expanded state 

 the thin and light valve offers a large surface to 

 the action of such eddies. 



On pouring a stream of water from the height 

 of a few inches through the auriculo-ventricular 

 opening into either ventricle of an excised heart, 

 the valve takes the shape of a funnel. The point 

 of this funnel projects into the middle of the cavity 

 of the ventricle. 



The segments of the valves cannot be driven 

 against the wall of the ventricles by the entry of 

 blood from the auricle. This is rendered impossible 

 by the central position of the papillary muscles, 

 as well as by the shortness of the chordae tendinees. In diastole 

 the papillary muscles are wide apart, and their tips diverge from one 

 another and point towards the base of the ventricle. Consequently the 

 flaps of the valves are 



1'Stf 



7,1/ f* m 



■: ft 



drawn by the cords out- 

 wards and downwards, 

 so that the tricuspid >m 

 orifice is thrown widely W*. 

 open. As the blood flows m 

 in from the auricle, the fej 

 eddies cause the valves 

 to float up and their 

 edges to approach each 

 other. At the end of 

 the auricular systole 

 the flaps are in such a 

 position that complete 

 closure immediately fol- 

 lows, so soon as the ven- 

 tricular pressure rises 

 to the slightest degree 

 above the auricular pres- 

 sure. Thus, on systole of the ventricles, the thin edges of the valves 

 are already in apposition, and the valves then shut with such rapidity 

 that in all probability no regurgitation takes place. 



From the results gained by manometric observations of the auricular 

 pressure, Krehl l concluded that there is no regurgitation into the auricle 

 so long as the conditions of the circulation are normal. 



Fig. 3. — Multiconvex upper surface of the closed 

 tricuspid valve.— Krehl. 



1 Arch./. Physiol., Leipzig, 1889, S. 289. 



