Pas ‧ teur, Louis /pæˈstɜːʳ/ BrE AmE
(1822–95) a French ↑ scientist who established the study of ↑ microbiology (=the study of very small living things such as ↑ bacteria ) , and proved that disease can be caused by ↑ germ s . He is also known for studying ↑ fermentation (=the process by which substances change chemically and become filled with gas by the action of bacteria) , and for inventing the process of ↑ pasteurization , as well as some ↑ vaccine s (=substances that are put into people's bodies to protect them from diseases) .