PATRICK J. FITZGERALD, M.D.
Department of Pathology. State University of New York, College Medicine at New York City. New York. N. Y.
The recent strides made in the study of the metabolism of biological organisms through the use of radioactive isotopes may be extended to the cytological level by use of the radioautographic technique. Cells or tissues containing a radioisotope are placed against photographic emulsion, and the particles from the isotope produce in the emulsion an image of the radioactive area of the object. After photographic processing, the emulsion areas affected by the radioactive object may be examined directly or after magnification by the visible-light microscope. The method makes possible the correlation between the presence or absence of an isotope label and the normal or pathologic features of the object being studied. The processed photographic emulsion is called a radioautograph, an autoradiograph, or, conveniently, an autograph. The technique is reliable, simple, and relatively inexpensive.
Shortly after Becquerel's accidental observation in 1896 that a frag- ment of uranium ore lying on a photographic plate caused darkening of the emulsion--an observation that led to the discovery of the natural radioactivity of uranium--London exposed a frog in a bottle to the emanations from radium, placed the frog on photographic emulsion, and, after processing the emulsion, obtained an image of the amphibian. Autographs of whole organs of animals injected with radium, of paraffin blocks of organs from animals given polonium, and autographs of histologic sections of animals given radiolead had been obtained by 1934. The first autograph of artificial radioisotopes was made in 1938.
There occurred a surge of interest in the technique of radioautography when I131 was demonstrated in the thyroid follicles in 1940. Subsequent progress has been rapid, particularly with the development of nuclear-track emulsions by the physicist, so that intracellular localization of some isotopes is feasible (25, 64, 89).