RADIOACTIVE TRACERS 95 



slightly active as compared with the inorganic phosphate indicated 

 that the latter cannot be produced from the former. This experiment 

 contradicts the view that the fats and inorganic phosphates are produced 

 by the breaking up in the milk gland of the phosphatides of the blood. 



If iron is used as a target in the cyclotron and bombarded with high- 

 speed deuterons (Livingood and Seaborg [1938]), about 1 atom in every 

 10 12 may be successfully transmuted into radioactive iron (half-life 

 47 ± 3 days) just as radioactive phosphorus was transformed. This 

 mixture of stable and negative electron-emitting radioactive iron atoms 

 ( 2 6Fe 59 ) can then be converted chemically to ferrous sulphate. If this 

 ferrous sulphate, containing radioactive iron, is fed to anemic dogs, it 

 will be absorbed and the new red blood cells which are formed will con- 

 tain hemoglobin made with radioactive iron. Since the radioactive 

 and normal atoms of iron are chemically inseparable, they will retain a 

 constant proportionality to one another. The radioactive atom can 

 thus act as a tracer to locate and follow the progressive use of iron atoms 

 in normal and in anemic animals, as was demonstrated by Hahn, Ross, 

 Bale, and Whipple [1940] and also by Miller and Hahn [1940]. New 

 hemoglobin containing radioactive iron was found by them to be detect- 

 able in the blood within about 4 hours. The iron was entirely used up 

 in 4 to 7 days. In this way the breakdown of red blood cells and hemo- 

 globin can be studied quantitatively. 



A radioactivated isotope of iodine 53I 126 emitting beta and gamma 

 rays has, according to Tape and Cork [1938], been produced having a 

 half-life of 13.0 ± 0.3 days. Experiments by Herz and Roberts [1941], 

 and Hertz, Roberts, Means, and Evans [1940], have indicated that 

 radioactive iodine is selectively taken up by the thyroid gland from the 

 blood stream within a few minutes after administration. 



The thyroid gland plays fundamental roles in the regulation of growth' 

 and of body heat. Its hormonal secretions are rich in iodine, and the 

 metabolism of this element, which appears to be of basic importance in 

 the proper functioning of the thyroid, is being studied with the aid of 

 radioactive iodine. 



In human beings with toxic goiter, the thyroid gland has been found to 

 take up practically all the administered iodine if the dose is 1 mg or less. 

 Basic studies are in progress on the rate and mechanism of the conversion 

 of the absorbed iodine into various chemical components of the hor- 

 monal secretions of the thyroid gland (Hamilton [1941]). 



The upward and lateral movement of salts containing potassium, 

 sodium, phosphorus, and bromine has been studied in growing and 

 transpiring willow and geranium plants. Stout and Hoagland [1939] 

 have shown that the path of rapid upward movement of salt is in the 



