In 1862, a French chemist named Louis Pasteur discovered that heat kills germs in liquids, preventing bacterial growth, food spoilage and foodborne illnesses. He used his discovery to invent methods that have been used for the last 150 years as a sanitary treatment for milk – which at the time was a prime source of TB. 

His experiment?  He exposed boiled broths to air in vessels that contained a filter to prevent particles from passing through to the growth medium via a long tube that didn’t allow dust particles to pass. Nothing grew in the broths unless the flasks were broken open- allowing him to conclude that the living organisms that grew in the broths came from outside rather than “spontaneously generated” within the broth (as was the conventional wisdom). This was one of the last and most important experiments disproving the theory of spontaneous generation. The experiment also supported germ theory.

Pasteur’s research also showed that the growth of micro-organisms was responsible for spoiling beverages, such as beer, wine and milk. With this established, he invented a process in which liquids such as milk were heated to kill most bacteria and molds already present within them. He and Claude Bernard completed the first test on April 20, 1862. This process was soon afterwards known as pasteurization.  Because of his study in germs, Pasteur encouraged doctors to sanitize their hands and equipment before surgery. Prior to this, few doctors or their assistants practiced the procedure of washing their hands and equipment.