1870.] 



four Orifices of the Heart, 



279 



ceiving their respective charges of blood from the auricles in exactly equal 

 and the same times. 



2nd. Equal volumes of blood enter the two ventricles during their dia- 

 stole, or else accumulation and stagnation would ensue : I am speaking 

 here of healthy ventricles. 



3rd. The ventricles are of equal capacities ; but 



4th. As the currents which traverse the tricuspid and mitral orifices are 

 of unequal velocities, the areas of those openings must be of such magni- 

 tudes that equal volumes of blood must pass through them in exactly equal 

 and the same times. The tricuspid having a slower velocity than the 

 mitral current, will necessitate the area of the tricuspid being proportion- 

 ally larger than the area of the mitral orifice. In a word, the synchronous 

 dilatation of chambers] admitting equal volumes of blood must entail such 

 a relation of area between the two inlets that 



the velocity through tricuspid _ area of mitral 

 the velocity through mitral area of tricuspid ' 



And if we assume the measurements previously found to be correct, 



1-25 



the velocity through tricuspid == Y 7 j5 ve ^ oc ^y through mitral, 

 =4 velocity through mitral, 

 i. e. the velocities of the currents of blood in diastole through the tri- 

 cuspid and mitral orifices are in the ratio of 5 to 7. 



It may be fairly asked what proofs can be given that the velocities of 

 the currents of blood which traverse the tricuspid and mitral orifices are 

 unequal, and that the mitral incoming stream possesses a stronger ventri- 

 cular dilating power than the current which enters the tricuspid to expand 

 and fill the right ventricle. I shall refer to this point shortly ; bat what- 

 ever may be the value of the reasons which will be adduced in support of 

 the above view, there can be no doubt, in fact, that the two orifices in 

 healthy hearts always differ in size, and the synchronous expansion of ven- 

 tricles with unequal inlets must inevitably lead to this result — that the 

 larger must admit a current of correspondingly smaller velocity than that 

 which traverses the smaller opening ; or, mathematically expressed, the 

 velocities of the incoming tricuspid and mitral streams must be inversely as 

 the areas of the orifices. 



From the data at which we have arrived, and estimating the mean 

 amount of the ventricular contents at three ounces (or five cubic inches, 

 nearly), although it must be confessed that this is an uncertain esti- 

 mate, we may readily calculate the average velocities of the currents 

 which traverse the four orifices. We shall consider the pulse to beat at 

 the rate of 70 per minute, and the periods of ventricular contraction and 

 dilatation to be in the ratio of 1 to 2, i. e. the ventricular contraction oc- 

 cupying one-third of the time between two pulses ; i. e. 



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