lab test 4
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The simplest way to make a slide of bacteria is to prepare a
Finding bacteria on a wet mount an be difficult for a beginner because bacteria are
quite colorless and transparent
a better way to observe bacteria for the first time is to prepare a slide by a process called
negative or background staining.
Negative staining consists of mixing the microorganisms in a small amt of ___________ and spreading the mixture over the surface of the slide.
nigrosine or india ink
These 2 pigments are NOT bacterial stains, they _________migroorganisms.
Do not penetrate.
Nigrosine & india ink ____________ to leave the organisms transparent & visible in the darkened field.
Obliterate the background
Although this technique has limitations, it can be useful for determining
cell morphology & size
Since no heat is applied to the slide, there is
- no shrinkage of cells
- (and more accurate cell-size determinations result than with some other methods.)
Negative staining is also useful for _______________that dont stain readily with ordinary dyes
When studying bacteria using a negative stain,
When using this method, make the smear thick at one end and feather-thin at the other, the ideal spot to study the organisms is
somewhere in between the thick & thin areas.
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