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I was doing histological slide preparation with rat's liver. There as a part of the microtechnique the fixed tissue had to be dehydrated using alcohol in the order 30%, 50%, 70%, 90% and 100% for 20-30 min each. This had to be done to get rid of the water (possibly extracellular) before it was embedded in paraffin for microtomy because paraffin is immiscible with water.

My question is how does the alcohol extract water out of the tissue?

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  • $\begingroup$ It's not about extraction. Alcohol just gradually replaces water. $\endgroup$
    – Ivan Neretin
    Nov 27, 2016 at 17:52
  • $\begingroup$ @IvanNeretin What is the need to treat the tissue with increasing concentration of alcohol solution? Why is it not treated directly with 100% alcohol? $\endgroup$
    – Tyto alba
    Nov 27, 2016 at 18:23

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The alcohol displaces water gradually through the process of osmosis. To prevent rupture of cells from the osmotic pressure, samples are immersed in a series of baths of increasing alcohol concentration.

After immersion in 95% or stronger alcohol, it is sometimes the practice to displace the alcohol with toluene or other non-polar solvent so that the specimen can be permanently mounted with paraffin or balsam.

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    $\begingroup$ I have a series of questions do you mind answering them? Like won't the cells shrink instead of getting ruptured? You know water moves from higher conc to lower conc i.e from inside of the cell to the water-less and acgohol rich extracellular region. $\endgroup$
    – Tyto alba
    Nov 29, 2016 at 6:15
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    $\begingroup$ The alcohol infiltrates the cell more rapidly than water leaves, in most cases. madsci.org/posts/archives/2006-03/1143666101.Cb.r.html If the movement of water were more rapid than ethanol, the cell would shrivel, as you describe. $\endgroup$
    – DrMoishe Pippik
    Nov 30, 2016 at 0:29

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