478 C. R. BARDEEN 



height of systole, one in diastole and the outlines of the two 

 superimposed shadows are compared. The pictures are taken at 

 the usual distance of two meters. Two intensifying screens are 

 used, one on each side of a photographic film. Drum tracings 

 of the respiration, carotid pulse and of the period of exposure 

 are made while the pictures are taken. The estimates of change 

 of heart volume from diastole to systole based on these plates 

 correspond well with the data given above as the following 

 table w^ill show (table 20). 



In the sitting position observations were made on sixteen in- 

 dividuals. For one individual two» sets of observations are 

 recorded in the table. During the change in heart volume from 

 diastole to systole blood from the ventricles is forced into the 

 pulmonary artery and aorta. Since the systolic picture was 

 taken as nearly as possible at the height of ventricular systole 

 it is possible that in most cases diastole had already begun in 

 the atria and some new blood had entered these chambers. 

 The actual output of the heart may therefore have been some- 

 what greater than that estimated from the change in the size of 

 the silhouette area fron diastole to systole. We have however 

 shown above from studies on cadavers that there is a tendency 

 to underestimate volume from silhouette area when the heart is 

 contracted so that to some extent the error due to diastole filling of 

 the atria is offset by the error due to underestimation of volume 

 from silhouette area. 



The average output per beat in the sitting position was esti- 

 mated as 37.8 per cent of the cardiac contents or 18.9 per cent 

 from^ each ventricle. This corresponds closely with the 20 per 

 cent estimate based on the work of Lindhard, as outlined above. 

 The lowest output was 27.4 per cent of the cardiac content or 

 13.7 per cent from each ventricle. The largest was 58.2 per cent 

 or 29.1 per cent frorn each ventricle. If we estimate the ventric- 

 ular content as 33^ per cent of the blood in the heart in the lat- 

 ter case the ventricle was nearly completely emptied at each 

 contraction while in the former case it was less than half emp- 

 tied. In eight out of the sixteen cases the per cent of cardiac 

 blood expelled varied from 39.2 per cent to 41.8 per cent or close 



