RAD 10 AUTOGRAPHY 



297 



RADIOAUTOGRAPHY 



ionization chambers, electroscopes, etc. 

 will depend on the nature of the prob- 

 lem and the degree of versatility de- 

 sired. For complete details see the 

 monographs listed below and the latest 

 manufacturers' catalogs. 



Renewed interest in the pioneering 

 technique of the autoradiograph has 

 resulted from the development of new 

 procedures and specially' prepared emul- 

 sions. Under favorable circumstances 

 it is now possible to achieve intra- 

 cellular localization of tracer elements. 

 See Gross, Bogoroch, Nadler, and 

 Leblond, Am. J. Roentgenol. Rad. 

 Therap., 1951, 65, 420-458 for a review 

 of the potentialities and limitations. 



The first step in a biological investiga- 

 tion would naturally be to decide 

 whether the use of isotopes is war- 

 ranted, on the basis of results expected 

 in relation to the economic investment. 

 The next step is a survey of the liter- 

 ature to ascertain whether isotopes 

 suitable for the purpose are available 

 and what measure of success could be 

 expected on the basis of similar experi- 

 ments. From these considerations a 

 choice of instruments and procedures 

 would be made. On the other hand, 

 a certain project may be warranted 

 and feasible, but rendered impracticable 

 by technical complications of various 

 kinds. 



For a source of materials one would 

 first consult the catalog issued by the 

 Oak Ridge Laboratory of the Atomic 

 Energy Commission. Herein are listed 

 the available stable and radioactive 

 isotopes together with prices, shipping 

 information, and official regulations on 

 clinical applications, health protection, 

 etc. Of the 96 elements, only He, Li, 

 B, Ne, N, O, Mg, Al, F, Si, and Fa lack 

 radioactive isotopes of suitable half- 

 life, leaving 85 elements whose employ- 

 ment is limited only by the ingenuity 

 and resources of the investigator. In 

 many cases the form of the material 

 may be specified: pure metal, inorganic 

 compound, labelled organic compound, 

 colloid, solution, etc. 



In addition a number of commercial 

 firms are engaged in supplying on order 

 and from stock an ever-increasing vari- 

 ety of organic intermediates and com- 

 pounds of metabolic importance syn- 

 thesized with tagged atoms in various 

 positions. If only small quantities are 

 needed, the investigator may conduct 

 a biological synthesis from plant or 

 animal sources in his own laboratory. 

 Although the nuclear reaction pile 

 now supplies the great bulk of radio- 

 isotopes, those who have access to 

 cvclotrons or similar machines should 



inquire about the possibility of getting 

 small amounts of the shorter-lived 

 isotopes. 



Studies involving radiation by alpha- 

 particles require the naturally-occur- 

 ring radioactive elements. The meta- 

 bolism of Pb, for example, may be 

 traced by means of those elements iso- 

 topic with Pb. 

 Radioactive Tracers in Biology. 2nd 

 Ed. M. D. Kamen, Academic 

 Press, New York, 1951, 429 pp. 

 Radioactive Indicators. G. Hevesy, 

 Interscience Publishers, Inc., New 

 York, 1948, 556 pp. 

 Isotopic Tracers and Nuclear Radi- 

 ations. W. E. Siri, Ed., McGraw- 

 Hill, New York, 1949, 653 pp. 

 The latter features a selected bibliog- 

 raphy to 1947 of papers on biological 

 and medical applications arranged by 

 elements, together with extensive tables 

 which aid in reviewing previous find- 

 ings and suggesting new possibilities. 

 The current literature is recorded in 

 the abstract journals and in Nuclear 

 Science Abstracts, published twice 

 monthly by the A. E.G. The "Annual 

 Reviews of Biochemistry" should be 

 consulted for comprehensive reviews 

 of special topics. 

 Radioautography — Written by C. P. 

 Leblond and R. Bogoroch, Department 

 of Anatomy, McGill University, Mon- 

 treal. September 12, 1951 — Radioautog- 

 raphy is a technique devised to define 

 the localization of radioactive sub- 

 stances within biological specimens. 

 The usual practice is to place a histo- 

 logical section as closelj^ as possible to 

 a phtographic emulsion, expose for a 

 suitable time interval and subsequently 

 develop as in ordinary photograph}'. 

 In place of light, the rays emitted by 

 the radio-isotope furnish the energy 

 necessary to transform the silver bro- 

 mide of the emulsion into photolj'tic 

 silver, which may then be developed 

 by photographic reagents into visible 

 black silver grains. Such grains overlie 

 the sites of deposition of the radio- 

 active substance in the histological 

 sections, thus giving a permanent, 

 visible record of the localization of this 

 substance. 



The use of the silver bromide grain 

 as a detector of radioactivity has four 

 advantages over other techniques: 1) 

 the effect of the radiation is cumulative, 

 and, therefore, minute quantities of 

 radioactivity may be detected if ex- 

 posure is sufficiently prolonged; 2) the 

 radioautographic image is a permanent 

 record; 3) the record is two-dimensional 

 and may be three-dimensional in case 

 of tracks; and 4) the smallness of the 



