microscope
Meaning of microscope: Diagnosis of many conditions rests on magnification, because healthy tissue and diseased tissue often part company only at cellular scale.
Definition of microscope
A microscope is an instrument that magnifies objects too small for the unaided eye, including individual cells, bacteria and the fine structure of tissue. Most work by passing light through a thin, prepared specimen and bending it through a series of lenses to form an enlarged image. Others build the image from a beam of electrons instead of light.
What do the main types do differently?
| Instrument | What it uses | What it is used for |
|---|---|---|
| Light microscope | Visible light and glass lenses | Routine tissue sections, blood films, urine sediment, cultured organisms |
| Electron microscope | A focused beam of electrons | Viruses, kidney filtering membranes, the internal machinery of a cell |
| Dark field microscope | Light angled so only scattered rays enter the lens | Thin, poorly staining organisms seen glowing against a black background |
The gap between the first two is not simply a matter of stronger lenses. Visible light cannot resolve two points closer together than roughly half its own wavelength, so a light microscope reaches a hard ceiling no amount of extra magnification can push past. Electrons behave as far shorter waves, which is why an electron beam resolves structures a light microscope cannot register at all.
Why is magnification central to diagnosis?
A great deal of medicine turns on what cells look like. Whether an ulcer is inflamed or malignant, whether a kidney is scarred or actively injured, whether an organism in a wound is a chain of round bacteria or a rod, and whether the cells in a lump are orderly or chaotic are all questions answered by looking. The pathologist judges the size and shape of nuclei, how tightly cells are packed, whether they are dividing, and whether they have pushed past the boundary that normally contains them. None of that is available from the outside of the body.
What has to happen to a specimen first?
Tissue is rarely examined as it arrives. It is fixed so it stops decaying, set in wax or frozen so it can be sliced far thinner than a sheet of paper, mounted on a slide and then stained, because most cells are nearly colorless. A standard stain colors nuclei one shade and the surrounding material another, which is enough to reveal architecture. Further stains and antibody based methods can mark one specific protein, showing not just the shape of a cell but what it is making. Each of those steps takes time, which is why a report seldom follows a biopsy the same day.
Used in a sentence
The pathologist examined the biopsy specimen under a microscope to look for abnormal cells.
Good to know
A light microscope and an electron microscope serve different diagnostic purposes, since the electron microscope's much greater resolving power is reserved for structures too small for visible light to separate at all.
Word origin
Where “microscope” comes from
Formed from Greek mikros, meaning small, and skopein, meaning to look at or examine.