PROGRESS OF THE ISOTOPIC METHODOLOGY 



1019 



Such experiments, as those last mentioned can only be carried out l>y 

 making use of radioactive indicators while many of the clinical analytical 

 determinations discussed do not necessitate the application of isotopic 

 tracers. We can determine the water content of the body by following 

 up the dilution of antipyrin determined by the usual chemical methods, 

 we can label red corpuscles instead of radioactive bodies with carbon- 

 monoxide, the concentration of which is determined chemically, the 



100 



80 



T3 



C 

 O 



60- 



Z40- 



0} 



c 

 o 

 a. 



E 20- 



o 



O Men 



• Women 



■+ incJicarss double poinr 



o o 

 o 



^ ^ 





nen 

 Torai -0^% •^ 



Women -O- •• 



Age 



30 



60 



90 



Fig. 18. — Change of the mixing rate of sodium ions 

 in the circulation with age. 



plasma volume can be measured by following the dilution of Evans 

 Blue. The application of radioactive tracers in these investigations is 

 not a necessity but a great convenience. Not so when splitting dynamical 

 equilibria, the only way to follow the path of iron in the organism is 

 to label it. The same applies to the tracing of pathways as that of glucose 

 carbon for example, discussed above. 



The determination of the life-time of various molecular components 

 of the organism was a great advance, a classical example being the 

 determination of the half-life of saturated and unsaturated fatty acids 

 of the rat liver which, in the early experiments of Schoenheimer and 

 PviTTENBERG using deutcrium as an indicator and in later investigations 

 in which ^^C was applied was found to be 1 and 2 days. Recent investi- 

 gations brought out, however, that the type of molecules in an organ 

 can have very different life-times. The phosphatide molecules present 

 in the cytoplasma of the liver cells are turned over almost twice as rapidly 

 as those present in their nuclei. It was also found, that in the liver a 

 fraction of fatty acid molecules is renewed at a very much more rapid 



