166 ADVENTURES IN RADIOISOTOPE RESEARCH 



of the bone tissue already formed and the formation of new tissue in 

 the case of adult animals as well. 



The following examples may help to make the three ways of entrance 

 of the labelled atoms into the bone easier to understand. 



1) When solid salts are in contact with labelled ions of the solution 

 within a short time a distribution equilibrium of the labelled ions between 

 the surface layer of the solid and the solution will take place, as is seen 

 for example in the experiment described above. This phenomenon was 

 studied extensively by Paneth and his collaborators^ in the case ol 

 lead salt which were shaken with solutions containing labelled (radio- 

 active) lead ions. 



2) If we deposit for example lead electrolytically from a solution 

 containing labelled lead ions, the metallic deposit will be a labelled 

 one, just as the bone grown from blood containing labelled phosphorus 

 will contain labelled phosphorus. 



3) In investigating the exchange between metallic lead and a solution 

 of labelled lead ions, or vice versa, we find'^ a different behaviour to 

 that described above in the case of lead salts. The exchange in the case 

 of metal is not restricted to the uppermost atomic layer of the lead 

 surface; many atomic layers are involved in the exchange process. 

 This is due to the fact that the lead actually goes into solution from 

 certain parts of the surface, while lead ions are discharged, at other 

 parts. This is a much more effective process in bringing about an exchange 

 between the lead atoms in the solid and in the liquid phase than that 

 observed in the case of solid salts where only the uppermost atomic 

 layer is involved (within any resonable time) in the exchange process. 

 The entrance of labelled phosphorus into the bone will also be much 

 facilitated if it is not only the uppermost phosphate layer that is invol- 

 ved in the exchange process; if in fact the bone is destroyed at certain 

 places and rebuilt at others. In view of the important enzymatic actions^ 

 going on in the bone tissue such a reversible breakdown process will 

 easily occur. 



Summary 



By adding radioactive phosphorus (phosphate) to the diet of rats, the 

 metabohsm of the phosphorus atoms taken in with the diet can be followed 

 np in the animal body. An appreciable part of the phosphorus taken finds 

 its way not only in growing but also in adult animals into the t)ones, teetli, 

 muscles, and different bodily organs. 



IF. Paneth and W. Vorwerk, Z. phij,s. Chem. 101, 445, 480 (1922). 

 2G. Hevesy, Phys. Z. 16, 52 (1915) 



3 R. RoBisox, The Significance of PhospJwric Esters in Metabolism. Xew York 

 (1932). 



