If at some point new life stirs in dead, decomposing flesh, for example in the form of maggots, then for most people that is above all: disgusting. However, many thinkers from antiquity to modern times saw it as an example of “spontaneous generation”, the new emergence of life from inanimate things.
The Greek philosophers Aristotle and Empedocles, for example, assumed that some animals, such as worms, insects, eels or jellyfish, arise spontaneously, i.e. from processes of putrefaction and decomposition from inanimate matter. It only requires life-giving warmth. Through this “cooking” (pépsis) life arises. Later supporters of this idea of spontaneous generation were also convinced that lice were created from sweat, as well as mice and snakes from carrion and maggots from rotting cheese.
That this is not the case, and that on the contrary, living beings, namely bacteria, can even be killed or at least rendered harmless for a longer period of time by heating is now common knowledge – thanks to an experiment by the French scientists Louis Pasteur and Claude Bernard.
On April 20, 1862, 161 years ago today, the two researchers presented two meticulously sealed glass containers at the French Academy of Sciences, which they had filled with blood and urine from a dog six weeks earlier and stored at 30 degrees Celsius. Both liquids were already considered “perishable” at the time. But do they change state, due to microorganisms contained in or entering the liquids, as Pasteur assumed, or is this fermentation process purely chemical in nature, i.e. without the influence of bacteria, as Bernard suspected?
Rather, if Bernard were correct, the elevated temperature would have accelerated the chemical fermentation process, and the Academy members would have noticed unpleasant odors upon opening the container. But it turned out as Pasteur had expected: the noses of the academics were spared.
As long as liquids remain bacteria-free, even perishable ones like blood and urine, they stay fresh. It was the first of a series of experiments by Pasteur that ultimately led to “pasteurization”, the brief (at least 15 seconds) heating (to at least 72 degrees Celsius) of foods such as milk in order to kill any microorganisms that may be present or to inhibit their growth, that it is safe to consume for a certain period of time (the expiration period).
While it has since been clear to Pasteur that fermentation requires microorganisms, Bernard was not convinced and continued researching for a long time. And in the end both were right: Because food can also be fermented without microorganisms as long as the necessary enzymes are present in them, which are necessary for the chemical processes. In nature, however, they are only produced by microbes that do not constantly arise from “spontaneous generation”. That only happened once: when life came into being.
Read all the episodes of the “Tagesrückspiegel” column that have been published so far here.
