Abstract. The stereological procedures available for estimating volume, surface area and number of the structural components of cells and tissue are reviewed. The applications of stereology to the study of liver, mammary gland, lung and placenta are discussed with particular emphasis on the aspects of interest to veterinary pathologists. Stereology provides the cell biologist and the pathologist with a powerful tool for describing biological structure in quantitative terms at various levels of organization from the organ to the organelle.Histology occupies a central position in pathology, but has been one of the last branches to use quantitative methods routinely. In the past decade, quantitative morphology at the microscopic level has become necessary in the study of tissues and cells. Quantitation is especially valuable in studying structural and functional changes produced by disease.The use of quantitative data in the description of structural features is called morphometry; morphometric data can be obtained by various means including stereological analysis of tissue sections. Stereology is a technique based on geometric principles that allows the derivation of three-dimensional structures from two-dimensional sections of these structures. By stereological methods, the volume (V), surface (S) and number (N) of structural features in tissues and cells can be determined quantitatively.The study of biological structure, even in quantitative terms, is a sterile and obsolete science unless related to function. Cell biology has taught us that precisely defined structure is essential for life at the level of molecules, of cells and of organs, and that deviation from this may lead to disease. Cell biology also has shown that most cells contain the full spectrum of organelles, and has identified the functions of many of these. Stereological analysis of tissue sections, by determining the quantitative balance of organelles, can thus provide valuable information about structurefunction correlations and the functional capability of cells. A number of excellent reviews have dealt with the application of stereology to cell biology and human pathology [41, 48, 52, 571. This review deals with the application of stereology to veterinary pathology.
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