Theories of staining
* Physical theories :
1) Simple solubility e.g. Fat stains are effective because the stain is more soluble in fat than in 70% alcohol.
2) Absorption : This is a property by which a large body attracts to itself minute particles from a surrounding medium.
* Chemical theories :
It is generally true that acid stain basic element (cytoplasm) and basic dye stain acidophilic material (nucleus) however, this far from being complete truth, Indeed hematoxylin, which is an acid dye, does not stain the cytoplasm, but (in the presence of mordant) is one of the most widely used nuclear stains.
Development of staining methods
* A Weigert, a German scientist contemporary with Koch, had observed the use by Cohn and other, of various dyes to make clear the details of cell structures in histological preparations.
* The natural dyes carmine and hematoxylin were widely being used.
* Ehrlich improved methods, discovered by William Perkin a brilliant British chemist, of preparing very fine dyes from coal-tar distillates.
* In 1875, Weigert found that the dye methyl violet could be used to reveal bacteria in histological preparations.
* This method of making bacteria visible was adopted by Koch and soon came into wide use.
Staining
"Staining is an artificial coloration of a substance to facilitate examination if tissues, microorganisms, or other cells under under of microscope".
Objectives of staining
* To make microscope and semitransparent objects visible.
* To reveal their Morphology.
* To study various internal and external structures of organisms.
* To demonstrate purity of culture.
* To diagnose disease.
