DETERMINATION OF SIZE OF HEART BY X-RAYS 471 



would indicate that there is a tendency to underestimate volume 

 from silhouette area when the heart is contracted. On the other 

 hand of the 22 bodies in which the volume was overestimated from 

 the shadow area, the weight was overestimated in 16 and under- 

 estimated in 3 indicating that these hearts were more dilated 

 than is normal for diastole at rest. This same condition is, 

 however, also true of the hearts in which the observed volume 

 fairly closely corresponded with the estimated volume. Of the 

 fourteen hearts in this group in 10 the weight was overestimated, 

 in 2 underestimated. 



Of the total of 53 hearts studied in 15 the weight was under- 

 estimated from the silhouette area, in 30 overestimated. We 

 may therefore assume that the method used in preparing the 

 bodies tended in the main to cause a somewhat greater disten- 

 tion than is normal in diastole in the living under the conditions 

 described above. 



We may likewise estimate heart volume from heart-weight, 

 which we have assumed to be 0.55 per cent of the body weight. 

 To determine a formula to express the relation of heart weight 

 to diastolic heart volume we need to know the relation of heart 

 w^eight to heart tissue volume and the relation of the volume of 

 heart tissue to the volume of the heart and its contents in diastole. 



In order to estimate tissue volume from heart weight we have 

 to determine the specific gravity of the heart. Vierordt, quot- 

 ing Davy, gives 1049 as the specific gravity of the left ventricle. 

 I have estimated the specific gravity of a considerable number 

 of fresh dog hearts, of one unembalmed human heart and of 

 numerous embalmed human hearts. The method used was to 

 measure the displacement of the heart in oil and to estimate the 

 specific gravity from this. The heart was in each case freed 

 from extraneous substances but the subepicardial fat was left 

 in place. The chief difficulty met with was to get rid of air 

 bubbles. To aid in this the heart was cut into sections. For 

 exact work the displacement should be measured in a vacuum 

 but this was deemed unnecessary for the purpose in view. While 

 there were individual variations, due chiefly to differences in the 

 amount of subepicardial fact, the figure 1050 was selected as a 



