DETERMINATION OF SIZE OF HEART BY X-RAYS 457 



On testing this estimate on dissecting room material we have 

 obtained the data shown at the right in table 4, p. 444. The 

 bodies studied were all embalmed at the time of weighing but it 

 is assumed that the ratio between heart weight and body 

 weight was not thus markedly altered. The percentages of 

 divergence given are the percentages above or below the standard 

 adopted for the weight of a heart belonging to a body of a given 

 weight. Thus for a body weighing 50 K. we should expect a 

 heart weight of 275 gr. If the heart weighs 286 gr. we designate it. 

 + 4 per cent; if 264 gr. — 4 per cent. The average weight for 

 twenty-five adult male hearts was 2,0 per cent below the stand- 

 ard, that of nine adult female hearts 1.1 per cent below the 

 standard. A foetus and one new born child had hearts below 

 the standard. One new born child had a heart considerably 

 above the standard. Of four young children two had hearts 

 below the standard; two had hearts heavier than the standard. 



Into the weight of the heart there enter four main factors, 

 (1) the heart muscle tissue, (2) the connective tissues of the 

 valves and supporting structures, (3) the intrinsic blood vessels 

 of the heart and the great vessels near their attachment to the 

 heart, and (4) the fat deposited beneath the pericardium and 

 elsewhere in the heart. Of these factors the heart muscle tissue 

 is dynamically the most important and varies in amount with 

 the dynamic demands on the heart. These demands to a large 

 extent are determined by the weight of the body and hence the 

 heat varies in size with body weight. The mass of the intrinsic 

 blood vessels of the heart probably varies normally directly 

 with the mass of the heart muscle. The great vessels near the 

 heart are relatively heavier than one might estimate so that the 

 relative weight of the heart found by different observers varies 

 to some extent with the amount of great vessel tissue included 

 with the heart. The fat likewise constitutes -no inconsiderable 

 part of the heart mass. To some extent it varies directly with 

 the relative amount of fat in the body as a whole. 



The two observers who have studied most carefully the rela- 

 tion of heart weight to body weight, Thoma and W. Miiller, 

 have excluded in some of their tables so far as possible the great 



