Everyone knows well those museum glasses with human foetuses or strange animals in a liquid, or as they are called: wet conservations.
There are various ways to preserve animals in a liquid. The most common is a 70% alcohol solution, but also formalin or glycol is used. The disadvantage with formaldehyde is its carcinogenic properties. In both formaldehyde and alcohol in the preparation will loose its colours.
The technique is most commonly used for reptiles and invertebrates. Animals, that, usually, are difficult or impossible to stuf.
Additionally you can with various other recipes create liquids that do more than just preserve.
A ‘Kajserling’ liquid f.e. preserves the colors better, its drawback is that adipose tissue is stained very bright.
If you look at the next picture, the difference between these two techniques is clearly seen. Both preparations are made about the same time. It is the ‘Kajserling’ solution on the left.
There is also a technique called clearing and staining. After the guts have been removed the animal is treated, first in a clearing-liquid, then in a staining-solution, and finally stored in glycol. The aim is to make the skeleton visible.