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Methanol & Other Fluids

Dehydrants for Paraffin Wax Processing


Methanol is sometimes used as a dehydrant, although it is more likely to be for a few blocks rather than a large hospital sized daily workload. It evaporates faster than ethanol and is more inflammable. These factors, along with its extra cost, make it a poor choice for routine dehydration.

Methanol is very poisonous, as little as 10 mL can cause blindness, and only a little more causes death. This is due to liver enzymes which metabolize alcohols. In the case of methanol these enzymes produce formaldehyde which then kills cells. The treatment is to give ethanol, as the enzymes preferentially metabolize this alcohol, allowing time for the methanol to be excreted in the urine.

Although it can be used as a fixative, methanol does not have a reputation for refixing tissues during dehydration, even when they are not completely fixed. This may be related to its lower efficiency as a dehydrant compared to ethanol. However, if applied for long periods to ensure dehydration of inadequately fixed material, it should be expected that morphology will be affected, and the quality of the final sections will be poor. As with other dehydrants, it is necessary to ensure the tissues have been properly fixed initially, both to avoid alcoholic fixation and to ensure complete dehydration within an appropriate period of time.

Other Fluids

Occasionally the use of fluids such as 2-ethoxy-ethanol, or something similar, is encountered. These fluids are often more expensive than the common fluids and are usually used for a specific purpose. They should not be expected to complete fixation of inadequately fixed material, and protein bound water may not be removed during the standard time periods they are applied. If they are used, it should only be on properly fixed material as it is otherwise a waste of an expensive reagent.