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ADVENTURES IN RADIOISOTOPE RESEARCH 



jected to that found after a given time is also stated. Furthermore, the 

 diluting volume is expressed in percent of the rabbit's body weight . 

 We shall first compare the rate of disappearance of sodium, chlorine, 

 and bromine from the circulation. This comparison encounters no 

 difficulties since practically the sole outlet of these elements from 

 the circulation is the extracellular body fluid, though some ^^Na is 

 taken up by the bone apatite (Hahn et ah 1939). No great diffe- 



FiG. 2. Rate of disappearance of various labelled ions from the plasma. 



rence is found between the rate of passage of sodium, chlorine, and 

 bromine through the capillary wall but the values obtained for dif- 

 ferent rabbits show fairly large variations. These variations are to some 

 extent due to differences in the size of the extracellular space. 



A comparison of the rate of passage of potassium, phosphate, and 

 water with that of sodium, chlorine, and bromine encounters some 

 difficulties since potassium, and the same applies to phosphate and 

 water, has an additional outlet into the tissue cells in contrast to the 

 first mentioned group. The amount of ^-K lost by the blood after the 

 lapse of a given time is the resultant of the amount penetrated into 

 the tissue fluids and that returned from the latter into the blood. When 



1 In experiments taking up to 1 hour, the amount of ^^Na lost by excretion 

 is less than 1 per cent of the amount administered. 



