CAPACITY OF THE VENTRICLES. l6l 



the heart. The two valves open in the same direction. The entire apparatus 

 is moderately distended with water by means of a funnel. By compressing the 

 heart-piece the contents are made to flow through the arterial valve into the 

 arterial portion. When the compression ceases, the contents return from the 

 venous portion through the venous valve into the heart. By means of this 

 apparatus the blood-current becomes continuous when the heart is com- 

 pressed in rapid succession, and the movement of the pulse can be demon - 



Arterial Valve. 



Capillaries. 

 FIG. 64. Model of the Circulation by Ernst Heinrich Weber. 



strated. The latter does not extend beyond the capillary region because the 

 great resistance offered by the many pores of the sponge destroys the force 

 of the pulse-waves. 



More complicated models of the circulation, which, however, do not essentially 

 illustrate more than this primitive model by E. H. Weber, have been designed by 

 numerous investigators. 



CAPACITY OF THE VENTRICLES. 



As the heart creates the difference in pressure necessary for the 

 circulation of the blood by throwing a definite quantity of blood into 

 the roots of the two large arteries every time the ventricles are emptied 

 by systolic contraction, it is desirable to determine this quantity of 

 blood. 



As the right and left ventricles must contract simultaneously, and 

 as, in addition, the same quantity of blood must pass through the 

 lesser circulation as through the greater, it follows that the capacity 

 of the right ventricle must be equal to that of the left. It must be 

 remembered, however, that a moderate quantity of blood always remains 

 in the ventricle, as this does not empty itself completely, even at the height 

 of its contraction. 



Methods. i. The capacity of the ventricles is determined directly by filling the 

 chambers of the flaccid heart after death with a coagulable material and measuring 

 the coagulated mass. This is an uncertain method, because the pressure in the 

 living ventricles during their diastole, following the contraction of the auricles,* 

 is not known. 



2. Indirect Estimation. A. W. Volkmann, in 1850, estimated the capacity of 

 the left ventricle in the following manner. The cross-section of the aorta and 

 the velocity of the blood-current in the vessel are determined. From these 

 data the quantity of blood that passes through the aorta in a unit of time is cal- 

 culated. As the total quantity of blood in the body (jV f the body-weight) is 

 known, the time required for the passage of this quantity through the aorta can 

 easily be calculated. Finally, if the number of systoles that occur during the 

 time of circulation be known, the quantity of blood for each systole will correspond 

 to the capacity of the ventricle. On the basis of numerous animal experiments 

 Volkmann estimated the ventricular capacity to be equal to ^ of the body- 

 weight; or 187.5 grams f r a rnan weighing 75 kilograms. The accuracy of this 

 method also leaves much to be desired, because the velocity of the current in 

 the aorta, which according to C. Ludwig and Dogiel is subject to considerable 

 ii 



