Quantitative Studies of Weak Light Sources in Biological Systems by Means of an Image Intensifier

Several image intensifier systems have been calibrated for gain and single electron detection efficiency. When these intensifiers are coupled to conventional microscopes the combined system provides sufficient light to allow photographic recording in short exposure times of certain biological systems that would ordinarily not be photographable or would require undesirably long exposure times. The photographs also provide quantitative information on the amount of light entering the microscope objective. Experiments are described in which an image intensifier microscope system has been used to study bioluminescence, providing data on the temporal and spatial distribution of light output in several organisms. Other experiments are described in which the location of weak radioactive tracers has been possible in short exposure times, using thin overlying scintillators to provide the necessary light. System requirements are discussed for the extension of this technique to X-ray studies and fluorescence microscopy.