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XII. — On the Action of the Valves of the Mammalian Heart. By D. Noel Paton, 

 M.D., F.R.C.P.E., Superintendent of the Research Laboratory of the Royal 

 College of Physicians. (With Two Plates.) 



From the Research Laboratory of the Royal College of Physicians. 

 (Read 4th January 1892.) 



Few subjects are of greater practical importance than the mode of action of the 

 valves of the heart, inasmuch as these structures are so frequently the seat of patho- 

 logical changes which produce serious disturbances throughout the whole circulatory 

 system. 



On the general principles of the mode of action of the aortic and pulmonary valves 

 all investigators seem to be agreed. When we turn to the auriculo-ventricular valves 

 we find that, while in some of the best known text-books their action is considered as 

 so thoroughly investigated and completely understood as to merit no discussion, and to 

 require only the briefest description, in others the mechanism is admitted to be 

 imperfectly comprehended, and is described in the most obscure and indefinite manner. 



In all, however, it is stated that the valves are raised at the commencement of 

 ventricular systole to form a horizontal membranous septum between auricle and 

 ventricle, and to prevent the regurgitation of blood from the latter cavity. 



Foster alone alludes to the possibility of the valves acting without being raised in 

 this manner. 



This view was originated by Dr Richard Lower (Tractatus de Corde) in 1669. 

 Its general acceptance seems to be due to the following causes : — 



First. The anatomy of the heart has almost universally been studied in the relaxed 

 condition and by the ordinary methods of dissection. The sectional method has been 

 employed only by one or two investigators, and in each case with a special purpose 

 unconnected with the mode of action of the valves. 



Second. Various experiments on the dead heart have been accepted as illustrating 

 the action of the valves in the living condition. Lower describes the now well-known 

 experiment of cutting away the auricles and filling the ventricles with water through 

 tubes placed in the aorta and pulmonary artery, and in this way causing the cusps of 

 the auriculo-ventricular valves to be raised and applied to one another, so as to form a 

 horizontal membranous partition between the auricles and ventricles — the chordae 

 tendinese and papillary muscles playing a purely passive part in preventing the 

 forcing of the valves into the auricles. 



An experiment which in so many important points fails to imitate the actual 

 ventricular systole of the living heart cannot be deemed of much value. Yet probably 

 no experiment has had so powerful an influence in establishing the present conception 



VOL. XXXVII. PART I. (NO. 12). • 2 E 



