504 ISOTOPIC TRACERS AND NUCLEAR RADIATIONS [Chap. 24 



for an adequate survey; and (2) and more importantly, because a great 

 volume of work, only partly declassified as yet, was carried out during the 

 war by the Manhattan District Project (now U. S. Atomic Energy Com- 

 mission) and will appear in the extensive series of publications planned by 

 the Atomic Energy Commission. It therefore seems premature at this time 

 to discuss and criticize the literature on the natural radioactive series. 



The bibliography purports to include all publications through 1947 dealing 

 with stable and artificial radioactive isotopes as tracers in biology and medi- 

 cine and with the effects and differential behavior of isotopes in biological 

 systems; papers describing chemical syntheses or physical measurements 

 have not been included unless they also give data on biological application. 

 There is an introductory list of general references (Gen); otherwise, the 

 references are grouped according to element, listed alphabetically. Under 

 each element references are in turn listed alphabetically according to author, 

 and each is assigned the symbol of its element and a serial number. In 

 Chaps. 24 to 29 citations are made by use of these designations (e.g., Nail, 56). 

 Papers subsequent to the end of 1947 have been specifically omitted except 

 for those of particular importance {e.g., reviews) and those in which the use 

 of an isotope for the first time is recorded; it may be pointed out, however, 

 that Biological Abstracts now includes (starting with Vol. 21, No. 7, August- 

 September, 1947) a separate section entitled "Radioactive and Heavy 

 Isotopes," which contains abstracts of papers on the use of isotopes and cross- 

 references to pertinent abstracts in other sections. Furthermore, an abstract- 

 rng section covering a good part of current radiobiological and isotope 

 literature (mainly the American) is to be found in the new journal Nucleonics. 

 Finally, the U. S. Atomic Energy Commission now issues a series entitled 

 Nuclear Science Abstracts which includes sections dealing with biophysics, 

 biology, and medicine. 



The particular importance of isotopes in biology is related to the fact that, 

 for most of those elements which are constituents of protoplasm, artificial 

 radioactive species can be substituted for normally occurring homologues 

 and used as "tracers" of metabolism and other physiological processes and 

 that, in the case of many elements, enriched amounts of the rarer (or even 

 the more abundant) stable species can be introduced into biological systems 

 and also used as tracers. In addition the fate and behavior, in living systems, 

 of minute amounts of elements and compounds not regarded as essential to 

 life can be followed, as well as the biological performance of all sorts of labeled 

 substances and entities normal and abnormal to an organism. Thus, 

 certain absolute or relative properties of various atomic nuclei permit the 

 biological application of isotopes as tracers. 



Of considerable importance also is the study of isotopic behavior and effects 

 per se. This is particularly true of radioactive species in connection with 



