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What are the effects of air bubbles under the cover glass?

Found in: Microscopy FAQ

Air bubbles in wet mounts can also have beneficial effects. They may supply ciliates and other organisms with oxygen.

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Air bubbles (unless they are too large) are not always a big problem in wet mounts. If larger parts of the specimen are submerged in water, then these parts can be viewed without problems. Air bubbles may cause some problems, especially for beginning microscopists. But bubbles are not always a problem.

  1. Air bubbles that are too large may not be recognized as air bubbles.
  2. Air bubbles attract ciliates and other organisms, as they are a source of oxygen. These organisms can sometimes be seen to aggregate around the air bubbles. If algae or other photosynthetic organisms are present (which produce oxygen), then the ciliates may aggregate around them instead.
  3. Air bubbles can limit the movement of ciliates. This can be seen as an advantage or disadvantage.

Bubbles can be more problematic if the specimen is thin and flat (such as larger microtome sections or onion skin). In this case it is possible that bubbles are caught below the specimen and it can be more difficult to remove these bubbles. Hydrophobic, furry specimens (insect hair etc.) also catch a lot of air and water may not be able to reach all parts of the specimen. In this case it may be easier to use a hydrophobic mounting medium (Euparal etc.) or to add a small amount of detergent to the water to break the surface tension. The detergent may also remove some oil from the surface of the insect hair, which makes the surface repel water.

This post was written in response to a reader’s question.

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