Originally published in Chem. Soc. Journal, p. 1618 (1951). 



Faraday Lecture, delivered before the Chemical Society in 

 Edinburgh on March 29th, 1950 



99. THE APPLICATION OF RADIOACTIVE INDICATORS 



IN BIOCHEMISTRY 



G. C. Hevesy 



It is with a feeling of deep reverence that I am delivering this lecture 

 in commemoration of the great genius and pioneer Michael Faraday. 



Throughout the century which saw the birth of D Alton's atomic 

 theory and witnessed Faraday's fundamental discoveries, each chemical 

 element was considered to be built up of one kind of immutable atoms. 

 Radioactivity has completely changed this conception. As shown by 

 Rutherford and his school, we are witnessing here the decay and 

 birth of new atomic species, and it was soon recognized that some of 

 these, seen from the chemist's view-point, were just new editions of 

 well-known chemical elements. To quote a few examples, it became 

 clear that radio-thorium was chemically practically identical with 

 thorium, and radium-D or thorium-B with lead. 



The discovery of this extraordinary chemical similarity was due to 

 SoDDY, BoLTwooD, and a few other great chemists, and the new pheno- 

 menon was termed "isotopy" by Soddy. Amongst the non-radio- 

 active elements the existence of isotopes was first revealed in the case 

 of neon by Sir J. J.Thomson's study of positive rays, and then much 

 extended by Aston by means of his mass spectrograph. Owing to these 

 discoveries the realm of classical chemistry was enlarged by ever-growing 

 territories the ultimate size of which we cannot foresee. I do not venture 

 to give even a very condensed survey of these fundamental and far- 

 reaching advances, but shall confine myself to the discussion of the 

 application of radioactive isotopes as indicators in biochemical studies, 

 made possible by the above-mentioned great progress. 



Radioactive isotopes were first used in the field of inorganic chemistry. 

 The first application of this type was made at the Vienna Institute for 

 Radium Research early in 1913 by my friend Professor Paneth, now 

 Director of the Londonderry Laboratory of Radiochemistry in Durham, 

 and myself. In the years to follow radioactive isotopes were applied by 

 us, and by a small number of other workers, in various studies in the 

 field of inorganic chemistry, and these researches proceeded at a much 



6 1 Hevesv 



