228 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1947 



to determine how this process is retarded, for instance, by rickets and 

 then promoted by the administration of vitamin D, and how it is even 

 led in the opposite direction by Basedow's disease, but it has also been 

 possible to study the finer distribution of the strontium assimilated: 

 the strontium was found to accumulate in the hard bone tissue, and in 

 the case of bone cancer it showed a preference for the cancer tissue and 

 possible metastases thereof. Though straying from our subject, it 

 should be pointed out that this last case may be of value to the doctor 

 not only diagnostically but also therapeutically. Given a sufficiently 



i 2 3 4 5d 



FiGUEE 1. — The assimilation of iodine in the thyroid gland. Along the abscissa is 

 the number of days which has elapsed after tlie administration of a known extra 

 amount of iodine in food ; along the ordinate the percentage of this amount found 

 in the thyroid gland as measured by means of radioactive iodine : a, for healthy 

 persons; &, with benign goitre; c, with Basedow's disease; d, upon defective 

 functioning of the thyroid gland (myxoedema). (From J. G. Hamilton, Appli- 

 cation of radioactive tracers to biology and medicine, Journ. Appl. Phys., vol. 12, 

 pp. 440-460, 1941.) 



high concentration the radiation of a radioactive kind of atom has a 

 destructive effect on the cancer tissue. If the radiating substance is 

 selectively attracted by the cancer cells, as strontium by bone cancer, 

 this may eventually serve as the basis of a very effective therapeutic 

 treatment. On the other hand, for physiological applications of 

 radioactive isotopes as indicators it is a general rule that the destructive 

 effect of the radiation must be avoided by keeping the concentrations of 

 the radioactive isotopes sufficiently small. 



We shall leave it at these examples. They are sufficient to give the 

 reader an impression of what can be achieved with the tracer method 

 in research work and routine investigation, a method for which uses are 

 to be found in ever-increasing numbers and in even wider fields. 



