144 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1945 



of administration of the tracer element, the rate of turn-over of the 

 material in the organ concerned, and whether or not new tissues are 

 being laid down, i. e., active cell multiplication, is going on at the time. 



Radio sodium, an emitter of gamma rays, given to a patient by the 

 mouth as common salt, can be detected by means of a Gieger counter 

 within 2 minutes of administration, in the fingertips. The ele- 

 ment uNa 24 has a very short half-life of 14.8 hours, and less than 10 

 percent is eliminated from the body within the period of measurable 

 activity. 6 It is excreted by the urine and sweat glands. 



Radio iron fed to cows appears in the milk within 24 hours. It is 

 taken up selectively by the red corpuscles of the blood and by bone 

 marrow, and in anemic animals the uptake is over 50 times that of 

 normal animals. Its absorption depends on the organism's need for 

 iron and it is best administered in a series of small doses as the per- 

 centage uptake is greater under these conditions. It used to be thought 

 that the iron content of the body was regulated by excretion, but 

 observation with radio iron has shown that just as much iron is 

 excreted by anemic dogs as by healthy ones. 



Radio iodine is taken up rapidly and in large quantity by the 

 thyroid gland, which absorbs 5,000 times as much as other tissues. 

 The concentration of radio iodine (/?- and y-ray emitter) can be 

 raised in animals to a level which leads to the complete destruction 

 of the gland, yet the action is so localized that the adjacent parathy- 

 roid gland is unaffected (pi. 3, fig. 1). The activity of the unhealthy 

 thyroid gland varies markedly according to the nature of the disease 

 affecting it. In a state of overactivity (hyperthyroidism) the uptake 

 of radio iodine is rapid, and this is followed by a rapid loss of the 

 element. Loss of glandular activity is reflected in a very small uptake 

 of iodine. It is possible to classify different types of disease of the 

 gland by the radio-iodine uptake. In malignant disease of the thyroid 

 its cells, unfortunately, lose their capacity to take up iodine, so that 

 it is unlikely that cancer of this gland can be treated by the adminis- 

 tration of radio iodine. 



Radio carbon has been used in the study of plant metabolism and 

 quite revolutionary discoveries have been made, especially as regards 

 the capacity of plants to reduce carbon dioxide. Others besides the 

 chlorophyll-producing plants can reduce carbon dioxide, and the 

 latter, contrary to general belief, are able to do so in complete dark- 

 ness though the activity is less than one-twentieth of that in sun- 

 light. It takes 100 minutes for radio carbon to be built up into the 

 plant solids. Barley can synthesize sugar from radio carbon in 2 



• In designating a specific isotope of an element, the total mass Is written as a super- 

 scription on the right of the chemical symbol and the atomic number as a subscription on 

 the laft 



