368 ADVENTURES IN RADIOISOTOPE RESEARCH 



compounds, present in the blood. This difference is closely connected 

 with the fact that the first-mentioned compounds are at least partly 

 rejuvenated through enzymatic action in the blood itself, while the latter 

 are principally rejuvenated in the organs and carried from these in the 

 blood stream. The measurement of the rate at which, for example, 

 adenosintriphosphoric acid molecules are renewed can be conveniently 

 used to determine the amount of enzymes the presence of which enables 

 the exchange reaction to take place. 



References 



(DK.LoHMANN, Biochem. Z. 194, 306 (1928). 



<2) L. Hahn and G. Hevesy, Bull. Lab. Carlsherg 22, 188 (1938). 



