the First Sound of the Heart is produced. 



333 



brought face to face into close apposition, and are so far closed by 

 the mere pressure of the blood from behind. As soon as the 

 ventricles are filled with blood the systole commences. The apex of 

 the heart approaches the base. At the same time the musculi 

 papillares contract, and by means of the chordae tendineae, attached 

 to the margin of the valves, prevent the laminae of the valves and 

 the blood from being pressed backwards into the auricles. In this 

 action — the simple apposition of the laminae of the valves, and the 

 closure of the orifices by means of the musculi papillares and chordae 

 tendineae — there is no such tensive force exercised as would be 

 sufficient to produce the loud and characteristic first sound of the 

 heart. 



Further evidence on this point ma}' be found in another direction 

 — namely, in the fact that the first sound can be heard independently 

 of the existence and action of mitral and tricuspid valves. Aware 

 of the fact that in some of the lower animals, more especially in the 

 reptile class, the auriculo- ventricular valves exist in but a very 

 rudimentary form, I obtained permission to examine some of these 

 creatures in the Zoological Gardens, and spent many hours on many 

 occasions in the investigation, assisted by my valued friend Dr. John 

 Sibbald, who was at that time my clinical assistant at the Brompton 

 Hospital, and who is now Senior Commissioner in Lunacy in 

 Scotland. Having examined many animals, we finally decided that 

 the python (Python solurus) afforded the best illustration of the 

 occurrence of the first and second sounds of the heart. In the heart 

 of that animal, of which I present two drawings, copied by permission 

 from a preparation in the Hunterian Museum, it will be seen 

 that the structures which represent the auriculo- ventricular valves 

 are formed by a continuation of the septum of the auricles ; they 

 are merely muscular flaps, destitute alike of musculi papillares and 

 chordae tendineae, and are without means of producing valvular 

 tension. I may here add that in an animal of a totally different 

 class, namely, the kangaroo, the sounds were distinctly recognised, 

 though the valves, as seen in the second drawing (copied also by 

 permission from a specimen in the Hunterian Museum), are very 

 rudimentary in character. 



Objections will no doubt suggest themselves to the view above 

 expressed. For example, the clinical physician will say, " I am in 

 the daily habit of hearing a distinct murmur accompanying the 

 systole in cases of diseased heart, and apparently replacing the first 

 sound. On examining the heart after death I find the auriculo- 

 ventricular valves diseased, a condition w T ith which I therefore connect 

 the murmur." It will at once be seen that we have here to deal with 

 morbid sounds totally different in character, and totally different 

 in the seat and mode of production, from the first sound of the 



