PROGRESS OF THE ISOTOPIC METHODOLOGY 



1017 



atoms of haemin originating from glycine, an appreciable part of the i^C 

 administered will be incorporated into haemin in the first phase of the 

 experiment. Later, as the specific activity of glycine markedly decreases 

 with time, haemin of minute activity is synthetised only. When the 

 strongly active red corpuscles built up in the first phase of the experi- 

 ment terminate their hfe-cycle, they become phagocytised and the circu- 

 lating red corpuscles show correspondingly a decreased activity as seen in 

 Fig. 16("> which indicates the life-span of human red corpuscles in this 



2,00-, 



200 



days 



Fig. 16. — Activity of human red corpuscles at various times after 

 administration of glycine-"C-2. 



case to be 113 days. This principle was first applied by Rittenbekg 

 and Shemin^^^^ who administered i^N labelled glycine and determined 

 the change in the ^^N content of the haemoglobin of the red corpuscles 

 with time, making use of the mass spectrograph. 



We mentioned already that in the cancerous organism the life-span 

 of the red corpuscles is often found shortened. The possibility of labelling 

 erythrocytes synthetized within a limited time interval enabled Ehren- 

 STEIN to carry out the experiments described on p. 1008, which permit to 

 distinguish between the action of cancerous plasma on erythrocytes built 

 up in a non-cancerous organism and the imperfection of the latter due 

 to their formation in a cancerous organism. 



PERMEABILITY OF PHASE BOUNDARIES 



Radioactive tracers found an extensive and fruitful application in 

 the study of permeability of phase boundaries of the capillary wall, the 

 placenta, the blood brain barrier, the frog skin and numerous other 

 cases. 



