Pasteur discovered germs.
Louis Pasteur was a scientist who developed important vaccines and came up with the process of pasteurization for foods. He is credited with discoveries that laid the foundation for the study of microbiology and modern medicine.
In his work, Pasteur further developed the germ theory and proved that bacteria caused drinks like beer and milk to sour. To prevent this, he invented the pasteurization process which involved boiling, and then cooling the liquid to kill bacteria. The connection Pasteur made between germs and illnesses helped lead to the development of sterilization practices in medicine by surgeon Lord Lister.
Pasteur developed his first vaccine in 1879 when he came up with a vaccine for chicken cholera after realizing that chickens exposed to the virus became immune to it. He went on to create vaccines for anthrax, cholera, TB and smallpox.
After treating a young boy for rabies successfully, Pasteur rose to fame and his discoveries received even more attention. When the silk industry faced a major crisis in 1856 due to the loss of silkworms, it was Pasteur who discovered that healthy silkworm eggs were being attacked by microbes. After killing the microbes, silk production began again. Louis Pasteur's discoveries laid the foundation for many scientific advancements in the future.