THE PHENOMENA NOTED DURING EACH CARDIAC CYCLE 303 



While the direct determination of the capacity of the ventricles of 

 the excised heart presents no unusual difficulty, it cannot possibly 

 yield exact results, owing to the changes in the tonus and elasticity 

 of the musculature subsequent to the removal of the organ and our 

 inabihty to reproduce the rhythmic changes in pressure under which 

 the heart ordinarily works. The attempt has also been made to 

 measure the cardiac output by determining the difference in the volume 

 of the heart during its systolic and diastolic periods. Experiments 

 of this kind have been performed by Stefani,^ Knoll, ^ Johannson and 



Fig. 155. — Diagram op Roy's Cardiometeb. 



Tigerstedt,^ and others. They consisted in inserting a cannula into 

 the pericardial sac, and in registering the volumetric changes by 

 means of a suitable piston-recorder. But naturally, as even the 

 slightest increase in the pressure in this pouch tends to hinder the 

 relaxation of the heart, the resulting values cannot be said to be exact. 

 Moreover, as the pericardial membrane also envelops the auricles, it 

 cannot be avoided that the volumetric changes of this portion of the 

 heart are transferred to the recorder together with those of the ven- 

 tricles. Roy and Adami^ have employed round metal capsules, or 

 cardiometers, consisting of two hemispherical shells, and large enough 

 to contain the heart in its entirety. The space intervening between 



1 Archiv de le scienze med., iii, 1879, 7, and Arch. ital. de bioL, xviii, 1892, 119. 



2 Sitzungsb. der Wiener Akad. d. Wissensch., 1881, 82. 



3 Skand. Archiv fiir Physiol., i, 1889, 345. 



* British Med. Jour., ii, 1889, and Phil. Transactions, clxxxiii, 1892, 199. 



