DETERMINATION OF SIZE OF HEART BY X-RAYS 



473 



included. It is of interest to note that the heart of the dog 

 weighs more in relation to body weight than the human heart 

 does and is subject to wider variations. This is in accord with 

 the observations of Joseph ('08). 



In the human heart the percentage of the diastolic heart vol- 

 ume occupied by the blood in the .cavities appears to be greater 

 than in the dog, the percentage occupied by the heart muscle 

 less. In the study of embalmed cadavers the empty heart vol- 

 ume was found to vary from 33.8 per cent to 80 per cent of the 

 volume of the heart as a whole. The hearts, the outline of which 

 seemed most closely to correspond with radiographic outlines of 



TABLE 18 

 Relation of diastolic volume to the volume of the empty heart in the dog 



the living diastolic heart, showed an average percentage of about 

 49.4 per cent heart tissue, 50.6 per cent heart chamber space. 

 If the specific gravity of the heart be taken as 1050 and the per- 

 centage of diastolic heart volume occupied by heart tissue be 

 taken as 49.4 per cent we may estimate diastolic heart volume 

 from heart weight by dividing the latter by 1.050 X 49.4 or 

 0.5187. The results thus obtained may be compared with the 

 estimates given in tables A and B, in which the heart weight is 

 estimated from the body weight and this in turn from the sil- 

 houette area while the volume is estimated directly from the 

 silhouette area. The use of round numbers in the tables gives 

 rise to slight divergencies but otherwise the estimates of heart 

 volume based on silhouette area and those based on heart 

 w^eight correspond. 



