Another booklet in this series, _Neutron Activation Analysis_, discusses a new process by which microscopic quantities of many different materials may be analyzed accurately. Neutron irradiation of these samples changes some of their atoms to radioactive isotopes. A multichannel analyzer instrument gives a record of the concentration of any of about 50 of the known elements. One use of this technique involved the analysis of a hair from Napoleon’s head. More than 100 years after his death it was shown that the French Emperor had been given arsenic in large quantities and that this possibly caused his death. The ways in which activation analysis can be applied to medical diagnosis are at present largely limited to toxicology, the study of poisons, but the future may bring new possibilities. Knowledge is still being sought, for example, about the physiological role played by minute quantities of some of the elements found in the body. The ability to determine accurately a few parts per million of “trace elements” in the various tissues and body fluids is expected to provide much useful information as to the functions of these materials. Summary A large number of different radioisotopes have been used for measurement of disease conditions in the human body. They may measure liquid volumes, rates of flow or rates of transfer through organs or membranes; they may show the behavior of internal organs; they may differentiate between normal and malignant tissues. Hundreds of hospitals are now making thousands of these tests annually. This does not mean that all the diagnostic problems have been solved. Much of the work is on an experimental rather than a routine basis. Improvements in techniques are still being made. As quantities of radioisotopes available for these purposes grow, and as the cost continues to drop, it is expected there will be still more applications. Finally, this does not mean we no longer need the doctor’s diagnostic skill. All radioisotope procedures are merely tools to aid the skilled physician. As the practice of medicine has changed from an art to a science, radioisotopes have played a useful part. THERAPY A Successful Case A doctor recently told this story about a cancer patient who was cured by irradiation with cobalt-60. “A 75-year-old white male patient, who had been hoarse for one month, was treated unsuccessfully with the usual medications given for a bad cold. Finally, examination of his larynx revealed an ulcerated swelling on the right vocal cord. A biopsy (microscopic examination of a tissue sample) was made, and it was found the swelling was a squamous-cell cancer.