CAPACITY OF THE HEART. 651 



ment of the next beat, fths of the whole period. According to Cheveau, 

 however, the ventricular systole in the horse occupies only a little 

 more than ith of the entire beat; Sanderson's researches coincide with 

 this statement as to the great rapidity of that event. 



At each beat of the heart, the ventricles are supposed to be almost 

 completely, if not entirely, emptied ; the left ventricle is often found 

 in that state after death, especially if examined during the period of 

 the rigor mortis. On a section, the walls of that ventricle are then 

 seen to be so thick, from their contraction, as to have been frequently 

 described as being hypertrophied. Although the right ventricle, as 

 already mentioned, allows a little blood to escape back into its corre- 

 sponding auricle, yet both ventricles are supposed to throw practically, 

 equal quantities of blood ; for, unless this were so, the left ventricle 

 would receive either too little or too much blood from the synchronous 

 action of the right ventricle, the quantity of water lost, as vapor, from 

 blood, in its course from one ventricle to the other, through the lungs, 

 being insignificant, amounting to less than Jth of a grain, during each 

 beat of the heart. The quantity of blood thrown at each systole, by 

 the ventricles, was formerly said to be, in the adult, about 4 oz., which 

 was described as the normal capacity of each of those cavities; but the 

 most r*ecent researches have led to higher estimates, viz. ,.5.3 oz. (Val- 

 entin), 6.2 oz. (Volkmann), and even 6.3 oz. (Vierordt). Positive 

 measurements are impossible ; the results obtained rest on various cal- 

 culations in hsemadynamics, to be hereafter mentioned. The capacity 

 of the auricles is said to be rather less than that of the ventricles, but 

 the quantity of blood which they contain is sufficient to distend the 

 ventricles, as these are partly filled by blood flowing through the 

 auricles into them, before the occurrence of the auricular systole. 



The force of the auricular contractions cannot be measured. From 

 observations on the blood-pressure in the arteries, the force of the left 

 ventricle is estimated to be equal to about fath part of the weight of 

 the entire body ; whilst that of the right ventricle, is supposed to be 

 less than half that force. The difference in the average thickness of 

 the walls of the two ventricles, which is about as 3 to 1, affords one 

 ground for estimating the difference in their power. 



The dilatation of all the cavities of the heart is, at least chiefly, an 

 intrinsic or spontaneous act, and not simply a passive distension, caused 

 by the blood flowing from the veins into the auricles, or by that forced 

 by the auricles into the ventricles; for when the heart of an animal is 

 removed from the body, or even when its auricles are separated from 

 the ventricles, both sets of cavities not only contract, but dilate. In 

 neither of these conditions, however, does any internal pressure, or 

 dilating force, act upon their interior, like the blood in the living state; 

 the cavities of the heart must therefore dilate spontaneously, owing, 

 as already mentioned, to the relaxation of their previously contracted 

 muscular walls. This dilatation assists the entrance of blood into 

 them, by diminishing the resistance to the passage of that fluid; it 

 thus saves the waste which would occur in the employment of a special 

 dilating force. 



The heart in Man, as observed in the case of beheaded criminals, 



