424 C. R. BARDEEN 



diagraphy has the advantage of giving a graphic outhne which 

 theoretically at least, corresponds exactly in size to the contour 

 of the object casting the shadow and it is economical in material, 

 but it takes much time and skill to exercise and is subject to 

 errors when a moving organ like the heart is studied. Tele- 

 roentgenography with our modern machines is quick and accurate 

 but demands that a proper allowance be made for enlargement 

 of the heart silhouette due to divergence of rays. 



Fortunately this is relatively simple -when the distance from 

 the target to the plate is the usual two meters and the patient 

 faces the plate. 



The average distance of the heart contour from the front of the 

 chest is approximately one-third of the distance from the front 

 to the back of the thorax measured at the lower part of the 

 sternum during expiration. Albers-Schonberg ('08) has shown 

 that the greatest transverse diameter of the heart lies in a plane 

 parallel to the front of the thorax and at a distance of about 

 one-third of the distance from the front to the back of the thorax 

 at the level of the 6th thoracic vertebra. I have been able to 

 confirm this observation by studies on numerous cadavers and 

 on cross sections of the trunk and also to show that the average 

 distance of the contour of the heart which casts the outline of 

 the heart silhouette in parallel dorso-ventral rays is about the 

 same distance from a plane parallel to the front of the chest. 

 The contour of the apex is of course nearer the plate than the 

 contours of the right atrium and the left atrium (W. Guttmann, 

 '06) but we are concerned wdth the average distance of the heart 

 contour from the plate. I have substantiated these studies on 

 the cadaver by means of stereoscopic methods and half-distance 

 methods of study of the distance of the heart contour from the 

 plate in the living. Knowing the average distance of the heart 

 contour from the plate it is possible to calculate the percentage of 

 reduction which one must make of the heart silhouette in order 

 to get the true size of the heart contour. In round numbers the 

 silhouette area must be decreased one per cent for each three 

 centimeters of distance from the front to back of the chest and 

 a given diameter one per cent for each six centimeters. As a 



