1870.] 



four Orifices of the Heart. 



283 



interesting to observe that this interlacement is most dense near the apex, 

 where the incoming current impinges with greatest force, and where the 

 excess of momentum of the blood can be easier annihilated before it 

 changes its direction of motion to escape in systole from the chamber. The 

 remarks which belong to the right are equally applicable to the left ven- 

 tricle, and lead to the conclusion that the current entering through the 

 mitral orifice, as soon as the chamber is filled, loses its motion for a mo- 

 ment before the contractile force of the ventricle launches it forth in a 

 totally different direction through the aortic opening into the systemic cir- 

 culation. 



I will now return to the statement which I had left unproved, that the 

 velocities of the synchronous tricuspid and mitral currents are unequal, and 

 that the latter possesses a stronger ventricle- dilating power than the former. 



The argument to establish this point is very brief. 



The two ventricles being of unequal thickness and containing conse- 

 quently unequal quantities and weights of muscular fibre, will necessarily 

 require currents of blood of unequal momenta to overcome their respec- 

 tive inertia, fill their chambers, and complete their dilatation in exactly 

 equal and the same times. That is, 



the momentum of the mitral is greater than the momentum of the tri- 

 cuspid current ; 



or, in other words, 



the volume of the mitral column multiplied by its velocity is greater than 

 the volume of the tricuspid column multiplied by its velocity ; 

 but the volume of each current is the same ; hence, eliminating volume 

 from each side of the above, it is evident that 



the velocity of the mitral is greater than the velocity of the tricuspid 



current, the conclusion which was to be demonstrated*. 

 In concluding this paper, I would very briefly recapitulate the conclu- 

 sions at which I have arrived. I have proved, from the measurements 

 of the orifices made by Drs. Peacock and Reid, that the areas of the open- 

 ings in man are subject to a constant law, summarily expressed thus : — 



T _ P 

 M A* 



And the same result I have also obtained from my own measurements of 



* I have employed the word momentum as one in common use ; but the term vis viva 

 would have been more correct, inasmuch as the latter expression represents the mass of 

 a body in motion multiplied by the square of its velocity. In this case, therefore, while 

 the velocities of the tricuspid and mitral moving masses of blood are in the ratio of 5 

 to 7, the energy ot vis viva of the tricuspid is to the energy or vis viva of the mitral 

 current or mass as 25 to 49. This observation does not affect the reasoning employed 

 above, but shows the greatness of the disparity between the ventricle-dilating powers of 

 the two incoming currents. 



