DETERMINATION OF SIZE OF HEART BY X-RAYS 477 



amount of blood discharged from the heart at each systole. 

 While the results have been far from uniform the results of the 

 more recent work including that of Krogh and Lindhard ('12) and 

 Lindhard ('15) appear to indicate that the output of the human 

 adult heart at rest is not far from 1 cc. per kilo of body weight 

 per beat. Since the weight of the heart substance may be esti- 

 mated at 5.5 gr. per kilo, its specific gravity as 1050 and its vol- 

 ume at about 49.4 per cent of the volume of the heart in diastole 

 the volume of heart content in diastole may be estimated as 

 5.365 cc. per kilo. About 20 per cent of the blood in the heart 

 in diastole is thus sent into the aorta at each systole during 

 rest. If we estimate one-third of the blood in the heart during 

 diastole to be contained in each ventricle and one-third in the 

 two atria we have 60 per cent of the contents of the left ventri- 

 cle sent into the aorta at each systole during bodily rest. 



In the upright position the diastolic heart is smaller than in 

 the sitting position and in the sitting position than in the prone 

 position. It appears that to the lessened hydrostatic pressure 

 in the inferior vena cava and to the moderate exertion accom- 

 panying sitting and standing the heart accommodates itself by 

 beating faster, contracting more completely during systole, and 

 expanding less during diastole. Nicolai and Zuntz have shown, 

 however, ('14) that during severe exercise the heart expands 

 more during diastole than when at rest. Muscular action acts 

 as a pump to force blood toward the heart. In all probability 

 the heart also contracts more completely so that the output of 

 the heart is increased by pulse volume as well as by pulse rate. 

 The experimental work of Henderson and Barringer on the dog 

 which has led these investigators to opposite deductions does 

 not seem to me at all conclusive. 



In order to test the estimate of heart content in diastole 

 given above and to estimate the reduction in size of the heart 

 during systole we have devised with the collaboration of Dr. J. 

 A. E. Eyster, an apparatus for taking 'instantaneous' radiographs 

 of the heart at any desired period of the cardiac cycle. The 

 mechanism is adjusted to the carotid pulse. As a rule two 

 successive radiographs are taken on the same plate, one at the 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 23. NO 2 



