ABSTRACT
Methods for direct observation of tissues and cells are important in biological studies. They have been applied to botany, zoology, and human biology for healthy as well as pathological organisms. These various methods are based upon physical and chemical principles. They are used to obtain the finest possible knowledge of tissue and cell components. These techniques are used from light to electron microscopy, from the direct observation of sections to their automatic analysis with a computer. Histochemical and cytological methods are the result of a long history of experimentation.
