196 



D. RiTTENBERG 



Having determined the total urea in the human we next 

 calculated the volume of solution (in litres) that this amount 

 of urea would occupy were it uniformly distributed at a 

 concentration equal to that found in the blood. This volume 

 we call the urea space. It is calculated from equation 6. 



Total Urea Nitrogen=10 x B.U.N, x Urea space 



(6) 



in which B.U.N, represents the blood urea nitrogen in mg. 

 per cent. Some values for the urea space are shown in Table 



TIME DAYS 

 0.5 





-0.5 • 



Fig. 3. Calculation of the size of the urea pool. 



I. The urea space appears in these three subjects to be about 

 50 per cent of the body weight. These values are approxi- 

 mately equal to the total body water values which exist in 

 the literature. We have directly measured the total body 

 water of a subject by administering DgO as well as ^^N 

 labelled urea. The DgO and urea values are in excellent 

 agreement, indicating that urea is uniformly distributed 

 through all the water of the body. 



Knowing the rate of excretion of urea in the human, we 

 can set up a system in which we need not assume that the 



