334 Sir R. Quain. On the Mechanism by which 



heart. To make the explanation more simple, I will confine my 

 observations to two principal forms of mitral disease associated with 

 systolic murmnr, namely, first, imperfection in structure with 

 distinct regurgitation, and, secondly, induration, roughness, and 

 irregularities on the mitral valve. 



(a) In mitral regurgitation consequent on disease affecting the 

 margins of the valves, the auriculo- ventricular orifice remains im- 

 perfectly closed ; and when systole of the ventricle takes place, a 

 portion of the blood is driven backwards towards the auricle, the 

 remaining portion being sent forwards in its normal course towards 

 the orifice of the aorta. The murmur which is produced by the retro- 

 grade flow of blood, permitted by the diseased valve, is heard at the 

 apex of the heart ; but at the same time the healthy first sound may 

 almost always be recognised at the base of the heart, over the aortic 

 valves. 



(6) In a second form of disease of the mitral valve, there may be 

 roughness, induration, or other irregularities from the presence of 

 deposits on the external surface of the laminae which meet the cur- 

 rent of blood going towards the aorta and flowing parallel with the 

 surface of the valves. A murmur is there produced audible at the 

 apex, but also accompanying the current of blood towards the base, 

 where it can be heard, often masking by its loudness the first sound. 

 It is quite remarkable how slight the roughness or irregularity may 

 be on the laminae of the valves which produces a loud and definite 

 murmur. These murmurs, striking and characteristic as they are, 

 are merely accidental complications which occur at the moment of 

 the systole of the heart ; but they are unconnected with, and have 

 no relation except in point of time to, the healthy first sound, which 

 may be heard apart from, and independently of, them. 



The weight of evidence, then, is clearly against the possibility of 

 the structure or the functions of the auriculo -ventricular valves being 

 the source from whence proceeds the first sound of the heart. 



Two other phenomena occur synchronously with the systole of the 

 heart, and consequently with the occurrence of the first sound. 

 They are — (a) the contraction of the muscular walls of the ventricles, 

 and (b) the propulsion and movement of the blood from the ventricles 

 into the arteries. I shall first consider the supposed share which 

 muscular contraction has in the formation of the sound. 



B. The muscular contraction of the walls of the heart during systole is 

 not the source of the first sound of the heart. 



The sound produced by muscle during its contraction was first 

 described by Dr. Wollastou.* He compared it to " a sound which 



* ' Philosophical Transactions,' 1810. 



