Louis Pasteur (1822-1895) was a French chemist, biologist and microbiologist. Pasteur famously linked disease to germs, and discovered the existence of germs for the first time in the 1860s. Pasteur’s germ theory became a crucial element in our understanding of disease. Once it was understood that these micro organisms (germs) exist, carry and spread disease it was possible, to an extent, to prevent them from doing so. Pasteur had finally identified what causes infectious disease and why it spreads.

Pasteur conducted a now infamous experiment in which he used a glass flask with an S shaped neck, such as the one pictured. This S shaped flask became known as the ‘swan neck flask’. The shape of the flask was an integral part of Pasteur’s discovery. He partly filled the body of the flask with an ‘infusion’ - a nutrient rich broth. He then boiled the infusion killing any germs already present in the liquid - this process is known as pasteurisation.

Pasteur allowed the infusion to rest. Over time, he observed that the physical appearance, particularly the colour of the broth did not change. This he explained was because the germ particles in the air attempting to enter the flask had become became trapped in the s shaped bend. Therefore, they had not contaminated the liquid.

Pasteur the tipped the particles into the body of the flask and observed that the microorganisms appeared in the infusion and multiplied, spoiling the infusion.

This demonstrated that certain germ particles in the air caused the spoiling of the broth, disproving spontaneous generation – a previous leading theory of disease that claimed the air itself was to blame. From this Pasteur developed and published his germ theory of disease revealing to the world the existence of microorganisms and the role they play.

This item is on display in the Medical Science display case at the George Marshall Medical Museum.