The histological slide is a rectangular glass slide on which cells or very thin slices of tissues and organs were placed. These slices are called histological sections or tissue sections. For protection, the sections are covered by a thin sheet of glass glued to the slide, called coverslip.
Tissue or organ slices for observation under an optical microscope measure usually 5 to 10 µm in thickness, that is, 5 to 10 millionths of a meter.
Measurements used in Histology: 1 µm (1 micrometer) = 1 thousandth of a mm = 1 millionth of a meter.
Permanent histological slides are designed to last for many years. To obtain a permanent slide, cells or fragments of tissues and organs usually undergo a procedure called fixation. Fixation is carried out by chemical means (e.g. with formaldehyde) or physical means (e.g. by freezing).
Small fragments of tissues and organs subsequently submited to several procedures, after which they can be cut in a device the microtome to obtain histological sections to be observed under a light microscope.
Cells, as well as tissue and organ sections, are almost always colorless and need to be stained in order to be observed under a light microscope. Finally, the sections are covered with a glass coverslip for their protection.
Glass slides are also used to observe isolated cells, bacteria, protozoa and other microscopic objects.
Liver. Staining: hematoxylin and eosin (HE). Medium magnification.