High resolution, brightfield and fluorescence, light microscopic methods have been developed for examining living organs in situ. The methods permit study of the rate, duration, magnitude and direction of dynamic histologic, pathologic, physiologic and pharmacologic events. In addition, morphometric analyses of such living preparations can provide basic information needed to evaluate alterations induced by fixation and processing of these organs for electron microscopy. Most organs are amenable to such investigations. In anesthetized animals, the selected organ is trans-and/or epi-illuminated with selected wavelengths of monochromatic light, imaged with water immersion objectives and the resulting monochromatic optical images televised using silicon or silicon intensified target (SIT) vidicon cameras. Quantitation is obtained by interfacing appropriate analog and/or digital instrumentation with the electro-optical system. Under optimal conditions the resolution is 0.3 μm, essentially the maximum obtainable by light microscopy. As a result, imaging is possible of most intra- and extravascular cell types, their nuclei, nucleoli as well as some cytoplasmic organelles and inclusions. The use of vital dyes and fluorescent tracers along or in combination with physiologic and pharmacologic stimuli provides information about structural-functional relationships in these intact living organs during both health and disease
