Abstract: A fluorescence microscope with a movable stage has means to stop stage movement when a modified object, such as an abnormal cell, is detected. A beam-splitting plate with an interference coating is provided in the path of radiation from an amplitude modulated irradiation source, which plate is adapted to reflect a short-wave component of fluorescent radiation from an object, accepted by a respective recording channel, and to pass a long-wave component of said fluorescent radiation from the object, accepted by a corresponding recording channel. Outputs of the recording chnnels are connected to the horizontal and vertical deflection plates of a cathode-ray tube so that the slope of the luminous line on the tube screen is proportional to the relationship between the two wavelengths of fluorescent radiation emitted by the object. A movable light detector associated with the screen provides a signal when a modified object is detected, with the signal being used to stop stage movement.