New York City boasts a magnificently equipped Radium Institute, under the directorship of Dr. C. Everett Field. And an even more famous institution is that founded by the Mayo brothers, in Rochester, Minnesota, where these eminent surgeons had accumulated an entire gram of radium as early, at least, as 1920--the largest amount owned by private individuals. This great institution--now known as the Mayo Foundation--is no longer privately owned, but it is still under the direction of the Mayos. Radiotherapy (or, in France, _curietherapy_, in honor of the discoverer of radium) or the treatment of various diseases by radioactive substances, has not been applied so extensively as has treatment by X-rays (Roentgen rays), produced in vacuum tubes. On the other hand, the X-rays are not so effective (as usually applied) in the treatment of certain morbid conditions as are the more penetrating Gamma rays from radioactive substances; though the latter are essentially identical with X-rays--swift Beta particles, or negative electrons--of very short wave-length. To produce X-rays as penetrating as the Gamma rays, about two million volts would have to be “cut” on the discharge tube. The Alpha rays are not often used in medical practice, and have little penetrating power. They are stopped by 3½ cm. of air, or by a thin sheet of paper. They are employed only in the way of radium “emanation” (a gas) dissolved in saline solution, or by the use of needles upon which active deposit from radium emanation has been collected. “In either case the emanation water or the active deposit needles must be introduced into the system--whether intravenously or into the solid tissues,--otherwise the Alpha rays would have no power to act. In either case, too, they act along with the Beta and Gamma rays produced by the active deposit” (Lozarus-Barlow). Beta radiation is used only for superficial conditions and always in conjunction with Gamma radiation. “Instead of a radium salt, one of its products, viz., radium emanation, is often employed chemically. No essential difference is introduced by the use of this emanation excepting that its intensity undergoes a progressive diminution with time, since it falls to half value in 3.85 days. Early rodent cancer, certain conditions of the eyelids, some cutaneous non-malignant tumors and birth-marks, are treated successfully in this way.” Physicians of the Memorial Hospital, New York City, announced in October, 1925, that by filtering out 90% of the caustic Beta rays emanating from radium and the high voltage X-ray tube, and using principally the healing and stimulating Gamma rays, radiation treatment of cancer of the tongue, lips, nose, ears or other part of the head has been greatly improved.