RADIOACTIVE ISOTOPES 



211 



RADIOCALCIUM 



pared from pure elements or simple 

 compounds, the use of elements in com- 

 plex forms is limited by the amount of 

 sj'nthesis that can be accomplished. In 

 some cases synthesis of complex organic 

 compounds can be carried out most 

 readily by the introduction of simple 

 radioactive salts into an animal or plant 

 and the subsequent recovery from the 

 organism of complex substances that 

 contain the radioelements incorporated 

 in their structure. 



Three methods of detection of the 

 radioactive isotopes are commonly used : 



1. In vitro method: Most common is 

 the measurement of the radiation from 

 the isotope with either a Geiger-Miiller 

 counter or an electroscope. Tissues to 

 be examined are either ashed arid 

 measured or extracted and measured in 

 solution. The Geiger-Muller counter 

 is extremely sensitive but only gross 

 tissue localization is possible, since rela- 

 tively large amounts of tissue must be 

 extracted. 



2. In vivo method: Detection and lo- 

 calization of some isotopes that emit 

 penetrating Gamma rays are feasible 

 within the living body by placing a 

 shielded Geiger-Muller counter against 

 the body so that it will receive rays from 

 restricted areas. Thus Hamilton has 

 studied the accumulation of radioiodine 

 in the thyroid gland. 



3. Autoradiography (or radioautog- 

 raphy): Known since 1924 (Lacassagne, 

 A. and Lattes, J. S., C. rend. soc. d. 

 biol., 1924, 90, 352-353; C. rend. d. 

 I'Acad. d. sc, 1924, 178, 488-490) this 

 technique secures on photographic emul- 

 sions images representing the location of 

 radioactive elements in tissue and organ 

 slices that have been held in contact 

 with photographic films. Photographic 

 records of sections of fixed tissues con- 

 taining radioelements can be made by 

 simply laying the mounted unstained 

 sections on a photographic plate and 

 leaving them until adequate exposures 

 are obtained. Subsequently sections 

 are stained for comparison with the 

 silver deposit on the developed plate. 

 See distribution of thorium B (a lead 

 isotope) in animal tissues by B. Behrens 

 and A. Baumann (Zeits. f. d. ges. 

 exper. med., 1933, 92, 241-250). In- 

 teresting studies ha,ve been carried out 

 also by J. G.Hamilton on the localization 

 of radioiodine in normal and enlarged 

 thyroid glands. The deposition of 

 radiophosphorus and radiostrontium in 

 bones and osteogenic tumors has been 

 autoradiographed by Treadwell, Low- 

 Beer, Friedell and Lawrence. Radio- 

 phosphorus distribution in leaves and 

 fruit of plants has been studied by 

 Aruon, D. J.,Stout, P. R.,andSipos, F., 



Am. J. Botany, 1940, 27, 791. Accord- 

 ing to Hamilton J. G. (Radiology, 1942, 

 39, 541-572), Lindsey and Craig have 

 proved that the method is valuable in 

 the study of phosphorus distribution in 

 insect larvae. Gorl)inan, A. and Evans, 

 H. L., Proc. Soc. Exper. Biol. & Med., 

 1941, 47, 103 have similarly determined 

 the time in embryonic development 

 when the thyroid first accumulates 

 iodine. 



Space does not allow further review 

 of the many problems tliat can be in- 

 vestigated using radioactive tracer sub- 

 stances. See Hevesy, G., Ann. Rev. 

 Biochera., 1940, 9, 641-662 and Hamilton, 

 J. G., J. Appl. Physics, 1941, 12, 440- 

 460 and Radiology, 1942, 39, 541-572. 

 Theoretical considerations are discussed 

 by Hevesy, G. and Paneth, F. A., "A 

 Manual of Radiology," 2nd edition, 

 London : Oxford Univ. Press., 1938, 

 and in a popular review of the develop- 

 ment of the cyclotron by Abersold, 

 Paul C, Radiology, 1942, 39, 513-540. 

 For literature on nearly 400 radioactive 

 isotopes see Seaborg, G. T., Chem. Rec, 

 1940, 27, 199-285. The effects of radio- 

 elements on growth of cells, tissues, 

 and organisms have been considered 

 by Haven, F. L., and Hodge, H. C, 

 Growth, 1941, 5, 257^266. The Annual 

 Reviews of Biochemistry, volumes 8 to 

 11 contain many data on the use of tracer 

 substances. See review of mineral 

 metabolism by Greenberg, D. M., Ann' 

 Rev. Biochem., 1939, 8, 269-300. 



Radioarsenic (As™) half life 26.8 hrs. 

 Used as a tracer for the distribution of 

 sodium dihydrogen arsenate in rabbit 

 tissues by duPont, O., Ariel, I. and 

 Warren, S. L., Am. J. Syph., Conor, 

 and Ven. Dis., 1942, 26, 96-118. Highest 

 concentrations appear in liver, kidney, 

 and lungs. In lower concentration it 

 is found in muscle, bone, and skin. 

 Browne-Pearce tumor tissue takes sig- 

 nificant amounts but loses them within 

 4 days. Elimination is chiefly by 

 kidneys. 



Radiobromire (Br^z) half life 34 hrs. Perl- 

 man, I., Morton, M. E. and Chaikoff, 

 I. L., Am. J. Physiol., 1941, 134, 107-113 

 followed the uptake of very small doses 

 of radiobromine by various tissues of 

 rat and guinea pig. Highest concen- 

 trations appear in thyroids in both 

 normal animals and in animals with 

 thyroids made hyperplastic by the 

 pituitary thyrotropic hormone. 



Radiocalcium (Ca^^) half life 180 days. 

 Stored almost entirely in bone. Only 

 small traces are found in other tissues 

 (Campbell, W. W. and Greenberg, D. 

 M., Proc. Nat. Acad. Sci., 1940, 26, 

 176-180 and Pecher, C, Proc. Soc. 

 E.xper. Biol. Med., 1941, 46, 86-91). 



