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 

 are in the same position as shown in 

 the diagram of the illustration. 



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 90, the 

 polarization prisms are mounted parallel and the field of the 



FIG. 20. Polarization 

 Microscope 



