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



f Equal or almost equal volumes of blood received in diastole, 

 \ Equal or almost equal volumes of blood expelled in systole, 

 (3) Equal or almost equal capacities of ventricles, 

 are the main characteristics of a heart which is normal in structure and 

 perfect iu function. 



(1) In employing the words equal times with reference to the periods 

 respectively occupied by the contraction and dilatation of the ventricles, I 

 would wish to refer for a moment to the statements made by our leading 

 authorities as to the average duration of the systole and diastole of the 

 healthy heart. 



Dr. Carpenter states that the ventricular contraction occupies § and the 

 ventricular dilatation § of the time which elapses between two consecutive 

 beats of the pulse. Dr. Walshe informs us that the time from the commence- 

 ment of the first to the beginning of the second sound is, on an average, one 

 half of the time from pulse to pulse. Dr. Burdon Sanderson, in his Hand- 

 book of the Sphygmograph, says, " There are several facts not difficult of ob- 

 servation which show that the time occupied by the heart in contracting 

 is very much shorter than is commonly supposed. The first sound being 

 synchronous with the commencement of the contraction of the ventricles 

 and the closure of the mitral valve, and the second with the closure of the 

 aortic valves, it is clear that the interval between these two events expresses 

 the duration of the contraction of the heart. Xow the most unpractised 

 auscultator can readily satisfy himself, while listeniug to the sounds of a 

 heart contracting sixty times in a minute, that the time between the first 

 and second sounds is not equal to that which separates the second from 

 the first ; and that it cannot be admitted for a moment (as stated in our 

 leading physiological text books) that a heart occupies half of a second in 

 contracting." 



This statement is borne out in the last edition of Kirkes's c Physiology,' 

 edited by Morrant Baker, in which the periods of ventricular contraction 

 and dilatation are considered to be in the ratio of 4 to 7. Chauveau's ex- 

 periments on the living horse and the sphygmographic tracings of the 

 radial pulse in man, clearly indicate that the times of ventricular contraction 

 and dilatation are very different iu duration ; and the inferences which are 

 deducible from the study of the comparative areas of the four orifices will 

 fully substantiate the statement that the systole of the ventricles " is a 

 much shorter proceeding than is usually supposed." 



(2) And again, with regard to the words " equal volumes of blood " used 

 above, I need scarcely remark that the same volume (quantity, ounces, 

 cubic inches) of blood is not persistently and at all times received by and 

 thrown out of the heart at every complete revolution of the organ. The 

 reverse is, in fact, nearer the truth ; for the ventricles (though of course 

 always full from the impossibility of a vacuum existing in their interior) 

 vary considerably from time to time in their degree of fulness and expan- 

 sion. In profound sleep, or in the perfect rest and muscular relaxation of 



