n 



24 RADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



phase 1 is transferred to phase 2, then Eq. (1-19) becomes 



A2 = Ae,{l - e-^0 



(1-20) 



where A^ = amount of A in phase 2 at time t 



Aeq = amount of A in phase 2 at equihbrium 

 Equation (1-20) can be expressed as follows for purposes of graphical 

 analysis : 



^ A2 



2.3 log I 1 - 



A 



eq/ 



- -kt 



(1-21) 



In this case a semilog plot of (1 — Ai/Aeq) vs. t will result in a straight line. 

 Table 1-4. Accumulation of Ca*^ in the Rabbit Femur 



[From graph in R. O. Thomas, T. A. Litovitz, M. I. Rubin, and C. F. Geschickter, 

 Dynamics of Calcium Metabolism: Time Distribution of Intravenously Administered 

 Radiocalcium, Am. J. Physiol., 169: 568-575 (1952).] 



This treatment may be illustrated by the data in Table 1-4, which 

 were taken from the graphs of Thomas et al. (46) and which represent the 

 accumulation of injected Ca^^ in the bones of young rabbits. The data 

 are plotted in Fig. 1-4. It is noted that the maximum reaching the bone 

 (Aeq) is 5.0 per cent. The value of A: is estimated from the curve to be 

 0.022. The ecjuation for the data then becomes 



A2 = 0.05(1 - ^-0022') 



These workers found the corresponding equation for adult rabbits to be 



A2 = 0.023(1 - e-"«22t) 



This was interpreted to mean that the fractional rate of uptake k (and 

 therefore the mechanism) was independent of age. However, the bones 



