THE HEART BEAT. 



547 



chamber with a circular opening at one point. Over this opening is 

 placed a membrane of rubber dam with a central opening through 

 which the heart is introduced, as shown in the diagram. The rubber 



Fig. 233. — Diagram to show the arrangement of the Henderson cardiometer. The 

 recording tambour is inverted, so that the systole will give an up-stroke on the curve. 

 (After Hirschf elder.) 



membrane lies snugly in the auriculoventricular groove, making 

 an air-tight joint. The interior of the ball is connected by 

 stiff tubing with a recording tambour. By an arrangement 

 of this kind the ventricles are kept within an air-chamber closed 

 everywhere except at the outlet to the recording tambour. 

 Every change in volume of the ventricles will be recorded accu- 

 rately provided there is no leak. Moreover, these volume changes 

 may be given absolute values in cubic centimeters if the appa- 

 ratus is calibrated beforehand. The cardiometer furnishes a 

 convenient method of estimating directly the amount of blood 

 entering and leaving the ventricles under varying conditions, 

 as well as the changes in heart-volume that may result from 

 variations in tonicity. When the heart is beating slowly the 

 volume curve has the form shown in Fig. 234. During systole 

 the ventricles shrink in size as the blood is discharged into the 

 aorta and pulmonary artery — the up-stroke of the curve. At 

 the end of the systole, after the closure of the semilunar and the 

 opening of the auriculoventricular valves, the ventricles are 

 dilated rapidly by the inflow of venous blood. Henderson has 

 emphasized the fact that the filling takes place nearly as rapidly 

 as the emptying, owing doubtless to the fact that at the end of 

 ventricular systole the auricles are dilated under some pressure, 

 so that their contents escape at once into the ventricles as soon 

 as the intervening valves are opened. The diastolic curve comes 

 back nearly to the base line and then forms a shoulder (4) from 

 which it approaches gradually to the base line up to the moment of 

 auricular contraction (5). The period of gradual dilation of the 

 nearly filled ventricles, which on the curve is shown from 4 to 5, is 

 called the period of diastasis by Henderson. The heart cycle, so far 



