Final answer:
Louis Pasteur used beef broth in his experiments to show that microbes are airborne. He created a nutrient-rich environment by using beef broth and then used swan-neck flasks to demonstrate that airborne microorganisms do not contaminate sterilized broth.
Step-by-step explanation:
Louis Pasteur conducted experiments using beef broth to demonstrate that microbes are airborne. The purpose of using beef broth was to create a nutrient-rich environment that would support the growth of microorganisms. In his experiments, Pasteur boiled the beef broth to sterilize it and then placed it in flasks with long, twisted necks called swan-neck flasks. The design of these flasks allowed air to enter but prevented the entry of airborne microorganisms. This allowed Pasteur to show that if the swan necks remained intact, the sterilized broth would remain free of microbial growth.