DETERMINATION OF SIZE OF HEART BY X-RAYS 465 



years about 33 per cent underweight, the older children and 

 women 2 to 25 per cent underweight, the oldest age group 40 

 per cent underweight. 



In the males the relative weight of the cardiac fat compared 

 with the body weight averages about 0.077 per cent from the 

 second to the fiftieth year with 0.057 per cent as the minimum 

 for an age group, 0.091 per cent as the maximum. Below the sec- 

 ond year, due in part at least to emaciation, the percentage is 

 markedly less, after the fiftieth year, due in part to a relatively 

 large amount of general body fat, it is greater. In the females 

 the percentage of cardiac fat averages 0.073 per cent from the 

 second to the fortieth year. It is only 0.046 per cent in the sec- 

 ond year and is markedly less in the younger infants. It is 

 0.092 per cent in the 31 to 40 year age group and from 0.101 per 

 cent to 0.152 per cent in the older age groups. 



We may therefore assume that 0.08 per cent of the body weight 

 represents approximately the proportional amount of cardiac fat 

 except in early infancy, when it is less and after fifty when it 

 becomes greater. 



The intrapericardial part of the great vessels of the heart 

 makes up a much less important part of the weight of the whole 

 heart. The following table (table 16) based on data from W. 

 Mtiller shows that the intrapericardial part of the chief of 

 these vessels, the aorta and pulmonary artery weigh about 0.005 

 per cent of the body weight and that they weigh relatively 

 somewhat more in old age than in youth. The percentage of 

 body weight is based upon the average body weight given by 

 Mtiller for the age groups in which he has studied the heart 

 weight (table 8). 



d. Heart volume 



Estimation of the normal ratio between heart weight and 

 body weight while unsatisfactory because based in the main on 

 bodies made abnormal by disease has the advantage of a basis 

 of direct observation. Estimation of the normal volume of the 

 human heart filled with blood in the living can be arrived at 

 only indirectl3^ We may estimate it either from the size of the 



