430 C. R. BARDEEN 



At the base of the heart a purely arbitrary Hne must be drawn 

 since there is no simple line of demarcation between the heart 

 and the great vessels. If, however, the right and left margins 

 of the heart silhouette be connected by a line which curves 

 gracefully from the curve of the right margin into that of the 

 left we have a line which will include within the territory of the 

 heart the right and left atria and the cardiac extremity of the 

 pulmonary artery and of the aorta. A small portion of the left 

 auricle may be cut off by the line that curves toward the right 

 from the left border but as a rule this is insignificant (fig. 1). 



By practice in employing this method of outlining the heart 

 silhouette, which is essentially that of Mortiz and Dietlen, one 

 may acquire sufficient skill to make practically identical esti- 

 mates of the heart silhouette area when plates are studied at 

 widely different intervals. This is perhaps the best test of one's 

 own consistency with the method. Different observers may 

 establish slightly different methods of completing the outline of 

 the heart silhouette which will lead to slightly different estimates 

 of the heart silhouette area but these differences should not be 

 serious when careful studies are made of the anatomy of the 

 heart in the dead body in conjunction with the heart shadow in 

 the living. The extent of the area included within the outline 

 of the heart shadow may be quickly estimated with a planimeter. 

 If the outline is that of a teleroentgenograph the appropriate 

 reduction for ray divergence should then be made. 



The chief objection to the method of estimating the size of the 

 heart from the heart silhouette area as outlined above is that it 

 is not sufficiently objective. For this reason it has not been used 

 by a number of foreign and American investigators who have 

 made x-ray studies of the heart. Among these may be mentioned 

 Otten ('12), Groedel ('08), Claytor and Merrill ('09), Williamson 

 ('15) and Shattuck ('16). 



The most objective measurement that can be made of the 

 heart silhouette is that of the greatest transverse diameter. This 

 is probably the measurement most frequently' made. For 

 the study of comparative size the transverse diameter of the 

 heart shadow is compared with the transverse diameter of the 



