MICROSCOPY 



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Figure 4-11. Partially Crystalline Otoconiae (stones) of the Utricular Macula 

 (bone) of the Organ of Balance in the Middle Ear: Sectioned, and in Negative 

 Phase Contrast. Magnification 60 x . In addition to the sizes and shapes of the 

 stones, note their darker center (glycoprotein) and the bright lamellar periph- 

 ery (calcium carbonate). (Photograph courtesy of L F. Belanger, University of 

 Ottawa Medical Faculty, and of J. Cytology and Cellular Comp.) . 



recombined to interfere constructively or destructively (as in the case of 

 phase, above), and to present to the eye enhanced differences in density or 

 color. Before the light passes through the specimen it is plane-polarized by 

 passing through a crystal in which the light in all but one plane is absorbed. 

 The emerging, polarized light is split into two beams whose polarized planes 

 are rotated at right angles to each other after one has passed through a sec- 

 ond crystal (birefringent). One beam then passes through the specimen, 

 and the other around it. The one which passes through is rotated, absorbed, 

 and retarded in different places to an amount depending upon the arrange- 

 ments of the molecules ( — the term is "different optical paths"). The dis- 

 torted light is then recombined with that by-passed, and their interference 

 presents the image in different colors to the eye. If monochromatic light is 

 used, the image appears in the form of differences in intensity; if white light 

 is used, the image appears in the form of differences in color. Although it is 

 not as sensitive as the phase microscope to differences in structure, the inter- 

 ference microscope affords a wider field of view, can show subtle differences 

 as shades in color, and has permitted (optical) determination of the amount of 

 a particular absorbing material in the field of view. Since its inception, in 



