A tissue is one of the building blocks of an organism--either animal or plant. An organism is comprised of tissues, which are made up of individual cells. These cells share a similar structure (how they're built) and function (what they do). The study of tissues is a field known as histology. Histology is the study of the microscopic anatomy (microanatomy) of cells and tissues of plants and animals. It is commonly performed by examining cells and tissues under a light microscope or electron microscope, the specimen having been sectioned (cut into a thin cross section with a microtome), stained, and mounted on a microscope slide. Histological studies may be conducted using tissue culture, where live human or animal cells are isolated and maintained in an artificial environment for various research projects. The ability to visualize or differentially identify microscopic structures is frequently enhanced through the use of histological stains. Histology is an essential tool of biology and medicine.