Microbiology is the study of microorganisms that is the organisms which are of microscopic dimensions. These organisms are too small to be clearly perceived by the unaided human eye. If an object has a diameter of less than 0.1 mm, the eye can not perceive (or more correctly resolve) it at all, and very little detail can be perceived in an object with a diameter of I mm. Roughly speaking organisms with a diameter of 1 mm or less are microorganisms and fall into the broad domain of microbiology. Since most microorganisms are only a few thousandths of a millimeter in size. They can only be seen with the aid of microscope. As a direct consequence of the invisibility of microbes to the naked eye and the need for special techniques to study them.