The light conductor, or Lichtleiter, consists of two parts: (a) the light container with the optical device and (b) the mechanical part with the viewing tubes which are fitted to accommodate the anatomical access of the organs to be examined. The instrument is about 35 cm high, shaped like a vase and made out of hollow lead, covered with leather. A round opening on its front side is vertically divided in two parts. In one half, a wax candle is placed and held by an arrangement of springs so that the flame is always in the same position. Concave mirrors are placed behind the candle and reflect the light of the candle through the one half of the tube to the eye of the observer. A concave lens is placed on the side towards the “Lichtleiter”.
According to the width of the cavities to be examined, i.e. the ear, the urethra, the female urinary bladder, gunshot tracts, etc. different specula were used. These specula consist of blade-shaped prongs which could be spread open by using a screw device in order to expand the channels.
In this Frankfurt model light conductor by Philipp Bozzini, the two tubes for light and image transport lie side-by-side. This explains why the opening for the ocular is located off-centre (more to one side) on the back wall of the light receptacle; this is typical of the Frankfurt light conductor.
Light and image transport are separated in the light receptacle by inserting the so-called reflection tube. The reflection tube ensures that the light emitted by the light source does not interfere with image transport; in addition, the reflection tube divides the opening on the front wall, to which the various examination shafts are attached, for light transport and image transport.
Complete separation of the channels for light and image transport was necessary in Bozzini’s light conductor only when the "tube for angular light transport" (a laryngoscope shaft) was used; this was a shaft in which the direction of light or image transport at the shaft tip was deflected 90° by means of a mirror.
Bozzini's instrument, in his own words...
The Light Conductor
The main requirements for looking into the internal cavities of the living body are therefore:
I. To introduce a sufficient amount of light into these cavities.
II. To bring the reflecting light-rays back to the eye of the examiner.
To fulfill the first requirement you need
a) a physiological or pathological orifice
b) a light container
c) light conducting tubes
To fulfill the second requirement you need an additional tube for the reflecting the light rays - which I call for the sake of distinction - reflecting tube.
Excerpt: Philipp Bozzini’s "Lichtleiter, eine Erfindung zur Anschauung innerer Theile und Krankheiten", in Journal der praktischen Heilkunde, Berlin 1806.
The Light Sheath
One of the main requirements of the light is that the flame is kept with constant intensity at the same position. A wax candle which is stuck in a sheath made of iron or sheetbrass seems perfect to me...
The Light-Conducting Tubes
Since these tubes bring the light into the cavities of the living body they should have the following properties:
1) They must be light enough to introduce them without any discomfort into the physiological or pathological orifices.
2) Since the cavities are mostly pressed together one would only see a small spot, if the shape of the tube should not be variable...
3) The different cavities of the living body require different tubes. The shape and size of the tube is subject to the individual cavity to be examined.
4) The tubes must give passage to the light and must permit excellent reflection of the light as well.
5) After being introduced into the cavities, the tubes must be fixed on the middle part of the light containers.
In order to reach all these requirements I have classified the tubes into three categories:
1) tubes for big cavities (e.g. vagina, uterus after delivery etc...)
2) tubes for small orifices,
3) tubes which permit the view to not straight (oblique) directions.
Excerpt: Philipp Bozzini, Der Lichtleiter, Weimar, 1807