Colouration of small, pale animals

It is not very difficult to make decent microscope preparations for examination under a high resolution light microscope. You will need a colouration, called Hoyer’s medium. It is prepared according to the following recipe:

30 g Arabic gum
50 ml distilled water
20 ml glycerol
200 g chloral hydrate

Dissolve the gum in the distilled water. It may take several days, but moderate heating and a magnetic stirrer speed up the process. Let it happen in a flask with a stopper so the water does not evaporate along the way. Next, the last two ingredients are added and when the chloral hydrate is dissolved you filter the fluid through a tea strainer to remove the coarsest impurities from the Arabic gum lumps. The mixture should be stored in a bottle with a stopper (not rubber or cork) and is stable for many years. The bottle should be labelled with “corrosive” and “toxic”.
Whenever you make a preparation, start by placing a drop of the mixture on a glass slide. The tip of a needle is dipped into the drop and is moved so that the insect is affected by the tip and adheres thereto. The insect is placed in the drop and a glass slide is placed on top. You can heat gently on the preparation to remove any air bubbles. The preparation can now be examined under a high resolution microscope, but it is better to allow it to stay a few days if necessary at 50 ° C, which can kill any insects. If you want to store the preparation in a box, it should be surrounded with clear nail polish.
Insects in water or glycerine can be applied directly to Hoyer’s medium, but insects in alcohol or lactic acid should be washed first. A drop of alcohol in the mixture causes the material to escape to the sides, and lactic acid precipitates in decorative shapes, which complicates any observations. Preparations with Hoyer’s medium are, as far as we know, unlimited durable and good to use when insects must be determined properly with a high resolution microscope – especially when using phase contrast.