16 HISTOLOGY OF MEDICINAL PLANTS 
POLARIZATION MICROSCOPE 
The polarization microscope (Fig. 20) is used chiefly for the 
examination of crystals and mineral sections as well as for the 
observation of organic bodies in polarized light. It can, how- 
ever, also be used for the examination of regular biological 
preparations. 
If compared with the regular biological microscope, the 
polarization microscope is found characteristic of the following 
points: it is supplied with a polarization arrangement. The 
latter consists of a polarizer and analyzer. The polarizer is 
situated in a rotating mount beneath the condensing system. 
The microscope, of which the diagram is 
shown, possesses a triple “‘Ahrens”’ prism 
of calcite. The entering light is divided 
into two polarized parts, situated perpen- 
dicularly to each other. The so-called 
“ordinary” rays are reflected to one side 
by total reflection, which takes place on 
the inner cemented surface of the triple 
prism, allowing the so-called ‘“extra- 
ordinary” rays to pass through the con- 
denser. If the prism is adjusted to its 
focal point, it is so situated that the 
vibration plane of the extra-ordinary rays 
oe are in the same position as shown in 
Fic. 20.—Polarization the diagram of the illustration. 
Microscope The analyzer is mounted within the 
microscope-tube above the objective. 
Situated on a sliding plate, it can be shifted into the optical 
axis whenever necessary. The analyzer consists of a polari- 
zation prism after Glan-Thompson. The polarization plane 
of the active extraordinary rays is situated perpendicularly 
to the plane as shown in the diagram. The polarization 
prisms are ordinarily crossed. In this position the field of 
the microscope is darkened as long as no substance of a double 
refractive index has been introduced between the analyzer and 
polarizer. In rotating the polarizer up to the mark go, the 
polarization prisms are mounted parallel and the field of the 
