PROGRESS OF THE ISOTOPIC METHODOLOGY 



1013 



Lack of time prevents me from discussing another very important 

 and elegant application of radioactive indicators, the tracing of the 

 path of atoms in photosynthesis, which enlarged our knowledge of that 

 important field immensely. 



ANALYTICAL APPLICATIONS 



The analytical applications of radioactive indicators do not only 

 involve the determination of elements and compounds as, for example, 

 sodium, potassium or water present in the organism but also of particles 



0,20 



0,15 



0,)0 



0,05-- 



/ 



7^ 



L 



\ 



Normal subject 



Type 



30 60 90 



441— 

 20 I50min.24hr 

 Time 



Fig. 13. — Distribution of ingested tritium labelled water in the human. 



such as red corpuscles, of the plasma volume, of the extracellular and 

 intracellular water volume and so on. These determinations are all 

 based on the already mentioned dilution principle. Such determinations 

 were for a number of years first carried out by applying heavy water 

 as an indicator. 



After the availability of superheavy water, the radioactive tritiated 

 water, it is mostly applied in the determination of the water content of 

 the body. The result of such experiments carried out recently by Fallot 

 and Aeberhaedt(2^> is seen in Fig. 13. To a fasting subject 100 ml 

 with ^HgOg labelled water of 10 millicurie of activity is administered. 

 Blood samples are then taken at intervals. They show the largest tri- 

 tium concentration after 30 min and a constant somewhat lower value 

 after 120 min. That the 30 minutes value is higher than the equilibrium 

 value indicates that the resorption of water molecules from the intestine 

 takes place at a more rapid rate than their equal distribution all over 

 the body water. 



Later a decrease in the ^HgOg content of the body water sets in due 

 to excretion and from this decrease the half-time of the stay of the water 

 molecules in the body is calculated to amount to 9 days by a water intake 



