DETERMINATION OF SIZE OF HEART BY X-RAYS 439 



of the individual. The difference between the observed and the 

 estimated areas is divided by the estimated area and the resulting 

 quotient is the per cent of divergence for that individual. Thus 

 if the individual weighs 50 K. (110 lbs.) one would estimate a heart 

 silhouette area of 100 sq. cm. If the observed silhouette area is 

 110 sq. cm., it is 10 sq. cm. above the estimated or +10 per cent. 

 If the observed silhouette area is 90 sq. cm. it is 10 sq. cm. below 

 the estimated or — 10 per cent. The average of these divergences 

 for the group gives the average percentage of divergence 



For normal children below four years of age we have at present 

 no data as to heart silhouette area in relation to body weight. 

 Table A has been completed down to birth in order to give a 

 working basis for study of the size of the heart in these younger 

 children. The statistical data given by various investigators 

 as to heart weight in relation to body weight in young children 

 make it probable that the formula of the relation of heart sil- 

 houette area to body weight holds approximately true of young 

 children as well aa of older individuals. 



For children from 15 to 40 K. in weight (33 to 88 lbs.) the most 

 extensive data are those of Veith (table 1). He gives figures 

 showing the heart silhouette area of 80 boys (orphans) in the 

 prone position and of fifty boys and twenty-five girls taken 

 sitting by the orthodiascopic method. The general average of 

 the eighty boys in the prone position is 10.8 per cent above 

 expectation. Of twenty-five orphan boys sitting, twenty-three 

 of whom were also in the first group, the general average is 2.1 

 per cent above exceptation. We may therefore attribute the 

 major part of the excess size of the hearts of the boys of the first 

 group to the prone position in contrast to the sitting position on 

 which our standard table is based. Three of the boys in the 

 31-40 K. group and six in the 21-30 K. group have very large 

 heart silhouettes. If these be excluded the excess of size of the 

 averagfe shadow area about equals what would be expected from 

 the prone position. Of the other groups the twenty-five school 

 boys sitting show an average divergence of only —0.08 per cent 

 while the school girls sitting show an average divergence of 

 — 5.1 per cent. It is probable that the formula for the relation 



