How long should specimens be dehydrated in 90% alcohol?

The ideal duration for dehydrating specimens in 90% alcohol is typically around 1 to 3 hours. This duration allows for sufficient penetration and replacement of water in the tissue with alcohol, which is crucial for preserving the morphological characteristics of the sample and preparing it for embedding in paraffin.

Dehydration is an essential step in the histology procedure, as water must be fully removed from the tissue to avoid issues during the infiltration phase with the embedding medium. If the dehydration time is too short, residual water may remain in the tissue, leading to poor infiltration and a compromised specimen. Conversely, an excessively long dehydration process can lead to over-drying of the tissue, which may also adversely affect the quality of the histological examination.

The 1 to 3 hour timeframe thus strikes a balance, ensuring that the alcohol has enough time to effectively dehydrate the tissue without causing damage, making this answer the most suitable choice.