Rinse a stained slide until the water runs clear
The staining step is timed and the rinse is not. Learn why the rinse ends on something you observe, and why the beaker gets fresh water each time.
- A step can end on a clock or on an observation: Some steps are finished when the time is up. Others are finished when something looks a certain way, and reading which kind you are on is part of following a protocol.
- Rinse water stops being clean once you use it: Whatever the rinse took off the slide is now in the beaker. Dipping again into that water puts some of it straight back.
Prerequisites are inferred: pending teacher review.
Re-learn the skill with worked practice and clear examples.
Now use the difference between a timed step and a judged one, and handle a stain that goes where it should not.
The staining is given a time of five minutes and the rinse is given no time at all. What does that difference tell you?
Reviewed- A.Staining is controlled by the clock and the rinse is judged by what you see
- B.The rinse is so quick that writing a time down for it was not worth doing
- C.The rinse matters less than the staining step, so it does not need controlling
- D.Both steps are timed, and the time for the rinse is given somewhere else
Show the worked solution ▾
Answer: A. Staining is controlled by the clock and the rinse is judged by what you see
- Step 1: Ask what sets the result in each step: Contact time for the stain. Amount of loose stain left for the rinse.
- Step 2: Match the control to the thing being controlled: One needs a clock. The other needs an observation.
Why it's right: Each step is controlled by whatever actually determines its result. Colour depth depends on contact time, so that step is timed. The rinse is finished when there is nothing left to wash out, so it is judged by looking.
- B: The rinse can take one dip or several depending on the slide, so a time would be the wrong tool even if someone wrote one down.
- C: An unfinished rinse leaves residual stain across the specimen, which is exactly the defect the repeat instruction is written to prevent.
- D: There is no rinse time given anywhere. The instruction hands you a signal instead, on purpose.
Aligned to Handling, Preparation, Storage and Disposal · reading level ~grade 9
The stain is added so that it covers the slide without overflowing. What happens when it overflows?
Reviewed- A.The stain ends up on the bench instead of on the specimen
- B.The metaphase spreads would wash off the edge of the slide along with it
- C.Nothing at all, as long as the full five minutes of contact is still kept
- D.The slide has to be prepared again starting from the water bath step
Show the worked solution ▾
Answer: A. The stain ends up on the bench instead of on the specimen
- Step 1: Follow the liquid: Over the edge, onto whatever the slide is resting on.
- Step 2: Ask what that costs: A mess to clean, plus stain that is no longer sitting on the spreads.
Why it's right: Stain that runs off the glass is doing nothing useful and is now on the bench, the towel and your gloves. The volume was measured for the slide, so what leaves is volume the specimen did not get.
- B: The spreads are fixed onto the glass by the earlier steps, so they do not float off with a spill.
- C: Time does not help if some of the stain has run off. Contact time only counts for the stain still in contact.
- D: A spill is a cleanup problem rather than a reason to restart from the beginning of the preparation.
Aligned to Handling, Preparation, Storage and Disposal · reading level ~grade 9
- A student adds the stain over a paper towel and stops before it reaches the edge.
Fill these in as you work through the lesson.
- Giemsa stain (the blue stain used on the spreads):
- Endpoint (the thing that tells you a step is finished):
- Residual stain (what is left when the rinse is not finished):
- Submerge (briefly, in a beaker, not under a running tap):
Stain for minutes, which is a step ended by the . Then rinse by briefly the slide, the water, and repeat until the water no longer turns blue.
- Say what tells you the rinse is finished.
- Explain why the beaker gets fresh water rather than the same water again.
- Describe what a stain overflow puts on the bench.
Your first dip turns the water faintly blue. You tip it out, refill the beaker, and dip again. The second time the water stays clear, so the rinse is finished and the slide goes on to be viewed.