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Pasteur's "col de cygnet" (1859)

Pasteur's Col de Cygne

The Renaissance glass blowers of 16th Century Venice were the first to experiment with decorative glass flasks with long, curved necks, much like the neck of a swan. The items were imported into Persia under Shah Abbas I and became traditional glassware used in Shi’ite mourning rituals – known as “ashdan” or “container for tears”.

Louis Pasteur, the great French microbiologist, saw another use for these swan-necked vessels, or “col de cygnet”. In 1859 he adapted the idea by making flasks with extraordinarily long, curved necks that trapped dust particles in the narrow bend, but which still allowed air to enter into the flask itself. Broth boiled within the vessel as the neck was being made would remain free of growth for extended periods of time, but would quickly go cloudy if the liquid was tipped to come into contact with the dust trapped in the curve of the vessel’s neck.

The importance of this experiment in finally disproving the ancient theory of spontaneous generation cannot be under-estimated. The idea that life could generate spontaneously had been around for centuries and even in Pasteur’s day there were some scientists who still believed that it could explain why boiled nutrient broths suddenly became cloudy with microscopic lifeforms.

In an earlier experiment, Pasteur sealed the neck of the vessel containing the freshly boiled nutrient broth so that it was completely closed off from the outside world. (One of these sterile flasks, and its clear, unspoilt broth, can still be seen today in the Science Museum in London). But for some critics, this experiment was not enough to disprove the idea of spontaneous generation, arguing that the boiling had somehow killed off some vital spontaneous force that was present everywhere in the air. 

To answer this criticism, Pasteur had to devise a way of somehow letting the outside air into the vessel, but at the same time prevent the entry of the tiny organisms he could see under the microscope. With the help of the col de cygnet, he presented what he described as “unassailable and decisive” evidence that “no living microorganisms would appear, even after months of observation. However, if atmospheric dust were then introduced, living microbes would appear within two to three days”.

Pasteur’s experiments effectively showed that germs are the cause of disease and decay; that these germs are present in air; and that they will grow in a sterile, nutrient medium. He lent his name to the pasteurisation process of heating milk, wine and foodstuffs to preserve them for extended periods. Later in life he also experimented with both prophylactic vaccines to prevent infections and therapeutic vaccines to treat patients who had become infected. But it was his col de cygnet that enabled him to finally puncture the myth of spontaneous generation and demonstrate the existence of airborne microbes that can contaminate or infect anything from a piece of fruit to an open wound.