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Sir R. Quaiii. On the Mechanism by which 



G. The first sound of the heart is caused by the impact of the blood 

 driven by the action of the muscular walls of the ventricles against 

 the block produced by the columns of blood in the pulmonary artery 

 and aorta which press upon the semi-lunar valves. 



I would adopt the explanation suggested by my valued friend, the 

 late Dr. C. J. B. Williams, that " sound is a phenomenon resulting 

 from resisted motion." We hear it in the whistling of the wind in 

 the rigging of a ship ; we hear it when the waves break upon the 

 shore ; we hear it when the blacksmith strikes the anvil with his 

 sledgehammer ; we hear it in the gentle sounds of the ^olian 

 harp, and in the whispers emitted by the vocal chords when the air 

 passes over them from the trachea. Let us examine the condition of 

 the circulation with regard to this particular point, namely, resisted 

 motion. 



In this inquiry I have derived most important assistance from the 

 admirable and elaborate researches of Professor Bell Pettigrew, F.R.S., 

 first, on " The Arrangement of the Muscular Fibres in the Ventricles 

 of the Vertebrate Heart," published in the ' Philosophical Transac- 

 tions ' of the Royal Society, 1864, and, secondly, on " The Relations, 

 Structure, aud Functions of the Valves of the Vascular System," 

 published in the ' Transactions ' of the Royal Society of Edinburgh, 

 1864. These refer especially to the left ventricle, but, at the same time, 

 it is to be observed that what applies to this ventricle applies, only in 

 a lesser degree, to the right ventricle. Dr. PettigTew explains the 

 manner in which the column of blood, projected from the heart into the 

 aorta, is formed by the union of three columns, an arrangement which 

 results from the mechanism of the heart as fully described by him. 

 These columns ultimately unite into one before reaching the orifice 

 of the aorta. The columns have a spiral motion, which is the result 

 of the spiral arrangement of the musculi papillares, of the spiral 

 arrangement of the fibres composing the walls of the ventricle, as 

 well as of the spiral shape of the left ventricular cavity itself. These 

 points, illustrating the character of the flow of the current, are 

 shown in the blood-cast from the interior of the left ventricle of a 

 horse which, by permission of the President of the Royal College of 

 Surgeons, I am able to submit to your examination. 



By this spiral, or what might be called "rifle," motion, the 

 blood is seen to be directed against the segments of the semi-lunar 

 valves, which are thereby hastily thrown apart, the spiral current 

 being continued for some distance within the aorta. The beautiful 

 rifle mechanism here described is constructed with the definite objects 

 of giving precision to the direction of the moving bod}* against a 

 given point, and of securing greater velocity and force in that body — 

 the moving column of blood. We have, in fact, here represented in 



