the microscope

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the microscope
2012-09-14 06:30:26

chapter 3 intro to micro
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  1. 2 major concepts associated with the microscope
    • magnification
    • resolution
  2. magnification
    power, the amount an object is increased
  3. total magnification
    • power of the ocular lens times the power of the objective lens used
    • example)when using the scanning lens multiply its power (4) times the power of the ocular (10)to get total mag of 40
  4. resolution
    • the ability of the lenses to distinguish fine detrail and structure     and
    • the ability of the lenses to distinguish between 2 points a specified distance apart
  5. darkfield microscope
    • used for examining live microbes that are invisible in the ordinary light microscope , cannot be stained by standard methods, are distorted by staining and cannot be identified
    • used to identify syphillis  
  6. phase-contrast
    used for examination of internal structures of living organisms
  7. fluorescent microscope
    takes advantage of fluorescence-the ability of substances to absorb UV light and give off light at a visible wavelength, uses fluorescent dyes or fluorochromes, also used in fluorescent antibody techniques
  8. electron microscopes
    • uses a beam of electrons rather than light for energy. types include:transmission electron, scanning electron
    • increased magnification and better resolution
  9. prep of speci for light microscopy:
    following air drying of the slide, heat fixing, methanol(methyl alcohol)fixing

    adhere specimen to slide,kill infectious agents, prevents distortion
  10. staining
    • allows contrast of specimen from background material allowing you to be able to see the specimen
    • most bacteria are slightly negatively charged and therefore stains/dyes must be positively charged.these are basic dyes
  11. simple stains
    • are aqueous or alcohol solutions of a single basic dye. most commonly: crystal violet, carbolfuchsin, methylene blue, safranin, malachite green.
    • visualize basic shape and structures-but color is simply the color of the stain
  12. differential stains
    • gram stain
    • acid-fast stain
  13. gram stain
    the primary differential stain used for routine microscopy in the clinical lab
  14. acid-fast stain
    a special differential stain used for bacteria, such as the mycobacteria, which have special cell wall components that do not stain easily with the gram stain
  15. gram stain steps
    • 1.application of crystal violet (purple dye) primary stain.
    • 2.application of iodine (mordant) sets the stain
    • 3.alcohol wash (decolorization) acetone-alcohol
    • 4.application of safranin. counterstain or secondary stain
  16. special stains
    negative, endospore, flagella
  17. negative stains
    are used to reveal the presence of capsules which are protective structures found in some species of bacteria
  18. endospore stains
    are used to identify the presence of thick walled structures which are not penetrated by gram stains
  19. flagella stains
    some bacteria have flagella which enable them to move. they are too fine to be visible with gram stains and this stain is used