In the films, usually when the “mad scientist” is introduced, in his laboratory it is possible to observe various organs and creatures in a jar, with a liquid substance that is most likely alcohol. The liquid, in fact, has been used since ancient times to preserve these samples.
This technique, if done well, can preserve the tissues for centuries. In a nutshell, “alcohol is toxic to the types of microorganisms that would cause decay,” he told LiveScience Bill Carroll, professor of chemistry at the University of Indiana in Bloomington.
An example could be taken from the wine itself. To make the drink a yeast eats the sugar of the grape which, in turn, transforms it into alcohol. Yeast expels so much alcohol that concentration becomes toxic and is killed by its own process. The alcohol content of wine, about 14%, helps to preserve the drink for years.
The preservation of other organic material, such as DNA, tissues or even whole animals, requires a higher concentration of alcohol, said Katherine Maslenikov, responsible for the collections of fish at the Burke Museum in Seattle. For example, formalin (a formaldehyde gas solution dissolved in water) is often used to stop internal biological processes.
Alcohol at even higher concentrations, e.g. 95% ethanol, works as a dehydrant. Which means that it removes and replaces water in the cell, tissue or sample of the whole body. This technique is a common way to preserve DNA, according to a 2013 study in PLOS One magazine.