2ZoocUse of Iodine 131 purine a rediocutograpk of the chromatocram by placing the paper egainst phetoeraphic Film tn a dark room will show the positions of the radioective compounés even though the actual amounts present would have to be inereaseé a thousané or even a millionfold in order to be seen or weighed or studied by ordinary chemical techniques. Ss tied By conventional chemical studies, even with radioiodine, the iodine ng sutstances of the thyroid heave teer. separated into only three Inorganic fodide (such as that in todized table salt). 2 A frection having solubility characteristics similar to those of Sioéceyresine 2. (bre result of sfding two lodine atoms to a molecule to A fraction with solubility like that ov thyrozine, the substance sileved to be either the thyycti? hormone itself or sn essential part of that hormone. (Thyroxide is nede up of e dilodotyrosine molecule combined ining portion of another diiodetyrosine molecule, end When the thyroids of rats injected with radioiodine were studied by “chromautograms", 1.6. recdioautozraphs of chrometograme, as described above, radioactive spc: were found at the positions taken by pure inorganic Lodide, dilodotvyrosine and thyroxine, but in addition there were a fes of unexpectcd redioactive compounds. The most intensely radioactive of these unoxnectad spots hes seen tentatively identified as monolagetyrosine since 15 coineides exactly in position end shape with the cclored spot Obtained when ea relatively lerge amount (i.e. a few Be