What type of flask did Pasteur use to disprove spontaneous generation?

Pasteur used a swan-neck flask to challenge the idea of spontaneous generation. Also called a gooseneck flask, it had a long, narrow, S-shaped neck attached to a flask containing boiled broth or another fermentable liquid.

The design was simple but powerful. Air could still reach the liquid, yet dust particles and microorganisms tended to settle on the moist inner bends of the neck instead of falling into the broth. When the broth was boiled and left undisturbed, it remained free of visible microbial growth. If Pasteur tilted the flask so the liquid touched the contaminated neck, growth appeared.

This result supported Pasteur’s argument that microorganisms came from existing organisms carried by dust, not spontaneously from the broth or from air itself. The flask is often described loosely as a special “Pasteur flask,” but “swan-neck flask” identifies its distinctive shape. It was essentially a modified round-bottom vessel, not a volumetric, conical, or ordinary round-bottom flask.