274 



Dr. Herbert Davies on the Areas of the [Mar. 17, 



this the result of the small supply of blood which the left ventricle received 

 and impelled into the general system ? In any case a knowledge of the 

 existence of this law enables us to read the measurements of the orifices 

 and their respective ratios with increased interest. 



It would be interesting to pursue the application of this law in the study 

 of the various forms of valvular disease. I purpose, however, to return to 

 this subject at the end of this paper, and shall seek now to trace out the 

 reasons why the four orifices present such differences in the magnitude of 

 their areas. 



And as the foundations of our arguments we must admit the truth of the 

 two following propositions : — 



1st. That the ventricles and auricles act exactly synchronously respec- 

 tively; and 2ndly, that equal volumes of blood pass in exactly equal and 

 the same times respectively through any two corresponding orifices of the 

 healthy heart. 



1. "If we examine," says M. Marey " the lines traced by the right and 

 left ventricles, we find a most perfect synchronism in the respective com- 

 mencements and terminations of their contraction." 



" The examination also of a heart exposed during life confirms the 

 deduction ; for if we grasp the auricles or the ventricles, we cannot detect 

 the smallest interval between the contractions of parallel cavities." 



Again. Stethoscopic examination of the heart demonstrates the existence 

 of only one first sound and of only one second sound, although the causes 

 producing each of those sounds are twofold, inasmuch as they really reside 

 in two (right and left hearts), placed in close and intimate apposition to 

 one another. Under rare circumstances the sound which results from the 

 closure of the semilunar valves has been found reduplicated ; but although 

 such an event may occur from the non-synchronous fall of the valves, it is 

 clear that an unimpeded and uninterrupted circulation could not be main- 

 tained unless the two sides of the heart, or really the two hearts, contracted 

 and dilated exactly synchronously. Whether the organ acts violently or 

 feebly, with regularity or intermittently, the auscultator detects but two 

 sounds ; and even when its valves are diseased, its orifices irremediably 

 altered in diameter, and its muscular walls hypertrophied or atrophied, we 

 find the same law of synchronism presiding over the heart and its sounds, 

 normal or abnormal. 



Lastly. An examination by dissection of the fibres which compose the 

 walls of the ventricles, conclusively proves that these chambers must inevi- 

 tably act exactly synchronously. In Dr. Pettigrew's masterly account of 

 the arrangement of the muscular fibres in the ventricles of vertebrate ani- 

 mals, we find the following remarks made upon this point : — " The fibres 

 of the right and left ventricles anteriorly and septally are to a certain extent 

 independent of each other ; whereas posteriorly many of them are common 

 to both ventricles ; i. e. the fibres pass from the one ventricle to the other" 

 The drawings 49 and 50 in the memoir clearly prove how " the common 



