The desire to explore the interior of human body cavities is as old as medicine itself. Attempts to construct instruments to penetrate the depths of such cavities and to illuminate their interiors sufficiently to make them visible extend back well over 150 years. In their simplest form such instruments consisted of a cylindrical tube which was inserted into the cavity and which was equipped with mirrors to throw reflected light from outside sources upon the interior wall of the cavity.
Modern endoscopes are refinements of the earlier instruments. They consist of cither rigid or flexible cylindrical tubes. Their length and mechanical construction depend mainly upon the cavity to be explored. Some of them are still simple hollow tubes, some contain ordinary magnifying lenses, and others are equipped with elaborate optical lens systems, permitting either unobstructed visual observation or photographic recording. The latter instruments usually consist of two parts, a tubular sheath and the optical system, which can be inserted into the sheath. The sheath can also receive instruments such as catheters and surgical appliances. The cavity walls may be illuminated by an electric bulb or by reflecting mirrors mounted in the ocular end of the endoscope, or by a tiny light bulb mounted on the tip of the endoscope introduced into the cavity. According to the construction of the endoscope, the cavity o t be explored, and the desire of the physician to make visual observations or a photographic record, endoscopic instruments in use today may be classified in three. . .