APPLICATIONS OF ISOTOPIC INDICATORS 



941 



shall therefore now describe some applications of radiophosphorus. 

 These examples represent only a small percentage of the investigations 

 in which radio-phosphorus has been used as an indicator ; many of 

 the results to be discussed were obtained in Copenhagen. 



RADIO-PHOSPHORUS 



Owing to the great sensitivity of the Geiger-Miiller counter, which 

 registers 32p with an activity of only IQ-^ microcurie, some of the radio- 

 phosphorus administered can soon be located in all organs. Table 3 

 shows the distribution of 32p in the organs of the rat 4 hours after sub- 

 cutaneous injection of labelled sodium phosphate /'^^^ 



Table 3. — Distribution of ^^p between Dif- 

 ferent Organs in Rat, 4 Hours after Sub- 

 cutaneous injection of Labelled Phosphate 



Weight of the rat: 188 gm 



Organ 



Bones 



Muscles 



Liver 



Digestive tract . 



Skin 



Lungs and heart 



Blood 



Kidneys 



Spleen 



Brain 



While 4 hours after the administration most sap is found in the ske- 

 leton, muscles, liver and the digestive tract, with increasing time more 

 and more s^p becomes incorporated with the skeleton. 98 days after 

 the start of the experiment, 92 per cent of all 32p present in the rat, 

 which corresponds to about one half of the total amount administered, 

 is found in the skeleton. This result may be seen in Table 4. Most phos- 

 phorus taken up with the food, in so far as it is not excreted, ultimately 

 finds its way into the skeleton, where it replaces "old" phosphorus 

 which interchanges with the phosphorus present in other organs or is 

 excreted. 



From these results, however, no conclusions can be drawn concerning 

 the extent of renewal of the skeleton, as the labelled phosphorus, i.e. 

 phosphorus administered throughout the experiment, may be incorpo- 



