998 ADVENTURES IN RADIOISOTOPE RESEARCH 



that of deuterium by Urey and the production of artificial radioactivity 

 by the Joliot-Curie's. 



Due to the great kindness of Professor Urey we obtained, shortly 

 after his discovery of deuterium, diluted (0.5 mol %) heavy water and 

 could embark on the investigation: if and at what speed the water 

 molecules of the goldfish interchange with the water molecules of their 

 surroundings, and on the determination of the mean-life time of water 

 molecules of the human body and of its water content. In the last menti- 

 oned determination^^^) the method of isotope dilution being used which 

 was first applied when determining the minute amounts of lead present 

 in rock samples. If we administer 10 ml of heavy water, after the lapse 

 of some hours when the administered heavy water gets into exchange 

 equilibrium with the body water we find 1 ml of the latter to contain, 

 beside the minute amounts present in all water, 1/5000 part of the ad- 

 ministered heavy water, and the total water volume of the body works 

 out to be 50 litres. 



A year later concentrated heavy water became available and the above 

 mentioned studies were soon followed by others of greatest importance 

 carried out by Schoenheimer and Rittenberg. The first showed that 

 an appreciable part of the deuterium labelled higher fatty acids adminis- 

 tered to the mouse can be located in the fat deposits even if the animal 

 is losing weight. They demonstrated with these studies the dynamic 

 nature of fat deposits. These are constantly renewed. Their investiga- 

 tions much enlarged our knowledge of fat metabolism. They embarked 

 then on the study of protein metabolism, applying i^N as a tracer 

 which was determined, as was the deuterium content of the compounds 

 investigated, with the mass spectrograph. The results obtained in the 

 last mentioned studies, demonstrating the dynamic nature of protein 

 metabolism, proved to be of fundamental importance as well. This im- 

 portant subject will be discussed by Professor MacFarlaine who made 

 numerous contributions of great interest to this field. Though we 

 know today that the dynamic nature of protein metabolism is confined 

 to the metabolic i)roteins, thus to a fraction of the proteins present in 

 the organism only, this fact in no way reduces the great importance of 

 Schoenheimer and Rittenberg's early results. 



As already mentioned the production of artificial radioactive sub- 

 stances was discovered about the same time as deuterium. Frederic 

 Joliot's and Irene Curie's fundamental discovery was followed at 

 once by a study of Fermi and his colleagues who produced a very great 

 number of radioactive isotopes under the action of neutrons emitted 

 by mixtures of radon and beryllium. In the first application of an arti- 

 ficial radioactive isotope, that of phosphorus, the same method was used 

 in Copenhagen. Glass tubes containing radonberyhium mixtures were 

 immersed in 10 litres of carbondisulfide which absorbed a large fraction 



