94 APPLIED RADIOACTIVITY 



Radioactive Tracers 



Certain chemical compounds, when administered orally or intrave- 

 nously, tend to concentrate themselves in certain organs of the body. 

 It has recently become possible to make such chemical compounds 

 radioactive, so that these specific regions where the radioactive chemical 

 compound has concentrated may be irradiated without producing a 

 large systemic effect or any skin injuries. If the radioactivity has a 

 comparatively short half-life and the decomposition products of the 

 artificially radioactive material are not toxic, no harm will result from 

 its presence in the body, even if it is not promptly eliminated. 



If certain foodstuffs, such as, for instance, those containing calcium 

 and phosphorus, are made temporarily radioactive, then they can be 

 used as tracers by measuring the relative radioactivity of the tissue in 

 which deposits have taken place. Such radioactive indicators or tracers 

 have helped in the solution of certain therapeutic and physiological 

 problems. 



When radiophosphorus is used as a tracer, a small amount of acti- 

 vated sodium phosphate is added to ordinary sodium phosphate solution. 

 The path and deposition of sodium phosphate are traced and located 

 by the 1.7-million-volt electronic emissions. Estimates of deposition 

 are carried out by observing the decay, at a given time, by means of 

 a Geiger-M tiller counter tube and by comparing the results directly 

 with the decay of a similar standard at the same time. This method 

 avoids corrections for the rate of decay due to lapse of time. Thus, 

 if it is desired to determine the radioactive phosphorus content of the 

 bone of an animal to which an activated phosphate solution has been 

 administered, and hence to determine any exchange in the phosphate 

 of the bone, a known weight of bone ash from the animal is placed under 

 the counter tube and the intensity of electron emission is determined. 



The source of phosphatides in egg yolks, the diffusion of phosphate 

 ions into blood corpuscles, the mechanism of enzymatic phosphoryla- 

 tions as in alcoholic fermentation, and numerous other problems have 

 also been investigated with active phosphorus as an indicator. 



The use of radioactive sodium phosphate has been of great help in a 

 study of the formation of goat milk. Samples of blood and milk, taken 

 at intervals after the administration of labeled phosphate, were examined 

 for the activity of the phosphate in the blood and the various phosphate 

 compounds of milk. It was found that after three or four hours the 

 inorganic phosphate of the milk was replaced by the active phosphate 

 of the plasma. It was estimated that the time of formation of casein in 

 the gland cells was about 1 hour. The fact that a few hours after the 

 addition of the labeled phosphate the milk phosphatides were only 



