()00 ADOLF F. VOIGT 



t he uptake of lead by plants using a naturally occurring radioisotope 

 of lead. During the past 25 years the use of this technique has in- 

 creased immeasurably. The growth was slow at first since the early 

 work was confined to the elements at the bottom of the periodic table 

 for which radioisotopes occur naturally and the biological interest m 

 these elements is not overwhelming. The early 1930's was a period 

 of numerous discoveries of fundamental importance in physics. In 

 addition to the discovery of the neutron and the positron and the 

 development of "atom-splitting" ion accelerators, it was found that 

 radioactivity was not limited to the heavy elements, but that radio- 

 active isotopes could be prepared from every element in the periodic 

 table. The newly discovered neutron proved to be one of the most 

 successful tools for the production of these artificial radioactive iso- 

 topes and the ion accelerators, in particular the cyclotron, were soon 

 applied to the production problem both by direct action and as the 

 most powerful neutron producers then known. 



It is not surprising that the number of workers using these isotopes 

 in biological research increased rapidly as soon as the isotopes became 

 available. A review written in 1940 contains a hundred references to 

 work published prior to that time (12). Every institution that had a 

 cyclotron also had active research groups in biological applications of 

 the tracers it produced, but it was somewhat more difficult for people 

 outside these fortunate institutions to obtain tracers. With the end 

 of the war a small part of the nuclear energy reactors was turned over 

 to the manufacture of radioisotopes for general tracer research use. 

 In June, 1946, the Manhattan District, which operated the atomic 

 energy project, announced the availability for sale to accredited re- 

 search institutions of a large number of radioactive isotopes {13). 

 This met with vociferous approval })y the scientists of the country 

 who felt that this techniciue could be used to solve many perplexing 

 problems. The project as continued by the Atomic Energy Commis- 

 sion has been eminently successful. In the first year of its operation 

 a thousand shipments of radioisotopes \\ere made {14)- 



With the incomparably more available and less expensive radio- 

 isotopes that the nuclear "pile" supplies, the urge to do tracer research 

 spreads out from a few to almost all research institutions. The re- 

 duced cost puts this approach within the reach of many colleges whose 

 budget could never have afforded isotopes previously'. It is reason- 

 able then that many people will wish to do tracer research who have 

 not had personal contact with other men in the field from whom they 



