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



and force of the streams issuing from the two ventricles, the quantities of 

 blood expelled by the synchronous contraction of the two chambers must 

 be exactly the same, or else accumulation in the pulmonic or systemic sys- 

 tems would ensue, and the machine be brought to a standstill. 



As, therefore, the two ventricles contracting with unequal forces have to 

 expel equal quantities of blood in equal and the same time to unequal dis- 

 tances and to overcome unequal resistances, the perfect synchronism of 

 the ventricular contractions can be only obtained by an exact graduation of 

 the areas of the orifices of the aortic and pulmonary artery to the muscular 

 forces respectively impressed upon the contents of the two ventricles in 

 systole, and consequently to the velocities of the streams issuing from those 

 chambers. The area of the aortic must be therefore smaller than the area 

 of the pulmonic, and in such proportion that the normal average contents 

 (say, three ounces) of the left ventricle shall occupy exactly the same time 

 in passing through the aortic as is required by the three ounces of the 

 right ventricle in passing through the pulmonic opening. The greater 

 muscular power of the left, as compared with that of the right ventricle, 

 causes a corresponding greater velocity and force of the column of blood 

 issuing from its outlet, while the smaller area of the aortic, as compared 

 with that of the pulmonic opening, exactly equalizes the times occupied by 

 the contractions of the two chambers. Without such an arrangement in 

 the comparative areas of the two outlets, it is clear that the stronger left 

 would completely empty itself before the right ventricle had accomplished 

 the same function, and the synchronous action of the two hearts would 

 be thus rendered impossible. Equal quantities of blood are, however, in 

 the way described, made to pass exactly synchronously through the aortic 

 and pulmonic openings, but with, of course, unequal velocities, the blood- 

 particles which traverse the narrow aortic travelling with greater speed than 

 those which pass through the larger pulmonic orifice. Mathematically 

 expressed, the velocities of the streams through the orifices are inversely as 

 the areas of those orifices, or 



velocity through aortic opening _area of pulmonic opening 

 velocity through pulmonic opening area of aortic opening 



And if we assume the mean measurements of the orifices found in the 

 former part of this paper to be correct, 



the velocity through 1 1 sq. inch _ . . _ _ 



... \ = ~r — = — r X velocity through pulmonic opening 

 aortic opening J '75 sq. men J ° r 1 ° 



f= 1*3 time the velocity through pulmonic opening 



sl| time the velocity through pulmonic opening, 



or, in other words, the velocities of the currents through the aortic and 



pulmonic orifices are in the ratio of 4 to 3. 



The arguments which I have advanced respecting the aortic and pulmonic 



will be equally applicable to the tricuspid and mitral openings ; for : — 



1st. The two ventricles are exactly synchronous in their diastole, re- 



