DETERMINATION OF SIZE OF HEART BY X-RAYS 429 



considered definitely determined. In the position we have 

 chosen as a standard it is probable that a moderately deep in- 

 spiration increases the diastolic filling to a slight extent over 

 that in expiration. The negative pressure produced in the thorax 

 by the inspiration tends to fill the heart during diastole, while 

 no marked restraint is exercised by the pericardium. 



3. MEASUREMENT OF THE HEART SILHOUETTE 



Methods of measuring the heart silhouette vary. As a rule 

 the right and left margins of the heart silhouette are clearly 

 defined while above the heart silhouette merges with that of the 

 great vessels and vertibral column and below with that of the 

 diaphragm, liver and stomach. The apex of the heart is most 

 clearly defined when there is a well marked gas accumulation in 

 the stomach. Sometimes a Seidlitz powder is given a patient in 

 order to insure a well marked gas bubble in the stomach. The 

 pressure of an excessive amount of gas may, however, to some 

 extent distort the picture. As a rule if the patient is given a 

 glass or two of water immediately before the picture is taken 

 and is requested to swallow as much air as possible with the water 

 a gas bubble of sufficient size will be formed in the stomach to 

 aid in outlining the heart. But gas in the stomach does not 

 serve to make a clear demarcation between the shadow of the 

 heart and that of the liver. To complete the lower margin of the 

 heart shadow it is necessary to draw a line to connect the outline 

 of the left margin with that of the right margin of the heart. 



With practice it becomes possible to draw this line with fair 

 approximation to its true position. As one gets used to visualiz- 

 ing the heart one learns to continue the swing of the line from the 

 right side into that from the left side. I have drawn many 

 hearts in position in the dissecting room using an apparatus which 

 enables me* to draw a line perpendicularly above the margin of 

 the heart. By comparing these drawings with those made from 

 x-ray plates it becomes evident that the approximately correct 

 completion of the lower margin of the heart outline is less difficult 

 than one might expect. It is more difficult in fat than in thin 

 individuals. 



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



