the First Sound of the Heart is produced. 



337 



ring surrounding the base of the heart, with which also the muscular 

 walls are continuous, the sounds are conducted to the apex. 



Pathology confirms this view. It was observed by Dr. Stokes that 

 in the course of typhus fever the first sound of the heart gradually 

 disappears. After death it is found that the walls of the heart are 

 softened ; and this morbid state has been accepted as a proof that 

 muscular contraction is the cause of the first sound. The real 

 explanation is that the impulse of the heart is so feeble that it is 

 unable to produce the sound at the valves. The correctness of this 

 view is confirmed by the fact, recorded by Dr. Sfcokes, that the last 

 point at which the sound disappears is over these valves, and that it 

 is at the same point that the returning sound is first heard. 



With the object in view of further investigating this subject, I 

 requested my friend, Dr. Alexander Morison, to study the heart of a 

 turtle recently killed by holding it close to the ear as one holds a 

 watch when testing for deafness, and also by pressing it gently 

 against the ear. With this intention, I gave him an introduction to 

 the proprietors of the " Ship and Turtle " tavern, where he had the 

 fullest opportunity of carrying out the investigation. 



Dr. Morison writes to me : — " An opportunity was afforded me of 

 examining the hearts of two large turtles immediately after they 

 were killed. The heart removed from the body was easily provoked 

 into active contraction by a gentle tap with the finger, the contrac- 

 tion being sufficient to expel blood from the cardiac cavity. On 

 placing the ear close to the heart whilst thus contracting, no sound 

 could be heard ; on placing the ear lightly on the heart whilst con- 

 tracting, no sound could be heard. So far, therefore, as a turtle's 

 heart is concerned — no other that I know of has more vigour of 

 contraction after removal from the body — muscular contraction, as a 

 cause of cardiac sound, must be excluded." 



These facts and observations are, in my opinion, sufficient to prove 

 that the contractile action of the muscles of the heart is not capable 

 of producing the first sound of the heart. 



Having thus endeavoured to show that the cause of the first sound 

 is independent alike of auriculo- ventricular action and of muscular 

 contraction of the walls of the heart, I proceed to consider a third 

 event, the most striking and important of all those which occur during 

 the systole of the heart, that is, the propulsion of the blood contained 

 in the ventricles into the pulmonary artery and the aorta, and 

 herein to indicate what seems to me to be the agency by which the 

 sound is produced. 



