The latest development is a tiny silicon (transistor-type) diode detector that can be made as small as a grain of sand and placed within the body with very little discomfort. Scanners Many of the applications described in this booklet require accurate knowledge of the exact location of the radioactive source within the body. Commonly a detecting tube is used having a collimating shield so that it accepts only that radiation that strikes it head-on. A motor-driven carrier moves the counter linearly at a slow rate. Radiation is counted and whenever the count reaches the predetermined amount—from one count to many—an electric impulse causes a synchronously moving pen to make a dot on a chart. The scanner, upon reaching the end of a line moves down to the next line and starts over, eventually producing a complete record of the radiation sources it has passed over. SUGGESTED REFERENCES Technical Books _Radioactive Isotopes in Medicine and Biology_, Solomon Silver, Lea & Febiger, Philadelphia, Pennsylvania 19106, 1962, 347 pp., $8.00. _Atomic Medicine_, Charles F. Behrens and E. Richard King (Eds.), The Williams & Wilkins Company, Baltimore, Maryland 21202, 1964, 766 pp., $18.00. _The Practice of Nuclear Medicine_, William H. Blahd, Franz K. Bauer, and Benedict Cassen, Charles C. Thomas, Publisher, Springfield, Illinois 62703, 1958, 432 pp., $12.50. _Progress in Atomic Medicine_, John H. Lawrence (Ed.), Grune & Stratton, Inc., New York 10016, 1965, volume 1, 240 pp., $9.75. _Radiation Biology and Medicine_, Walter D. Claus (Ed.), Addison-Wesley Publishing Company, Reading, Massachusetts 01867, 1958, 944 pp., $17.50. Part 7, Medical Uses of Atomic Radiation, pp. 471-589. _Radioisotopes and Radiation_, John H. Lawrence, Bernard Manowitz, and Benjamin S. Loeb, McGraw-Hill Book Company, New York 10036, 1964, 131 pp., $18.00. Chapter 1, Medical Diagnosis and Research, pp. 5-45; Chapter 2, Medical Therapy, pp. 49-62. Popular Books _Atoms Today and Tomorrow_ (revised edition), Margaret O. Hyde, McGraw-Hill Book Company, Inc., New York 10036, 1966, 160 pp., $3.25. Chapter 9, The Doctor and the Atom, pp. 79-101. _Atomic Energy in Medicine_, K. E. Halnan, Philosophical Library, Inc., New York 10016, 1958, 157 pp., $6.00. (Out of print but available through libraries.) _Teach Yourself Atomic Physics_, James M. Valentine, The Macmillan Company, New York 10011, 1961, 192 pp., $1.95. (Out of print but available through libraries.) Chapter X, Medical and Biological Uses of Radioactive Isotopes, pp. 173-184. _Atoms for Peace_, David O. Woodbury, Dodd, Mead & Company, New York 10016, 1965, 259 pp., $4.50. Pp. 174-191. _The Atom at Work_, Jacob Sacks, The Ronald Press Company, New York 10010, 1956, 341 pp., $5.50. Chapter 13, Radioactive Isotopes in Hospital and Clinic, pp. 244-264. Articles