French scientist Louis Pasteur disproved the theory of spontaneous generation, the idea that certain organisms are ever-present in nature. For example, early scientists believed fleas came from dust and maggots from dead meat absent anything else.

Pasteur theorized and later proved that all organisms come from something else, that nothing exists in a vacuum. He extended his line of thinking to the realization that bacteria can cause problems. For example, grape juice will turn to vinegar instead of wine.

Killing the bacteria, Pasteur reasoned in 1864, results in grape juice that will always ferment into wine rather than vinegar. Pasteur’s methods involved raising the temperature then storing in a clean environment, a technique that became known as pasteurization.  

In 1882, Robert Koch discovered bacteria in milk was responsible for anthrax and these spores could be killed by Pasteur’s methods (winning him a Nobel Prize). Pasteurization applied to milk by chemist Earnest Lederle in 1810. Pasteur was also known for creating vaccines for anthrax and rabies. Through his discoveries about bacteria he also started the practice of keeping medicine clean. Pasteur died wealthy and famous but not from pasteurization.

Vaccines (Smallpox)

Smallpox was a killer, affecting royalty and peasants alike. When it didn’t kill, it oftentimes left victims permanently maimed. Besides eventually eradicating smallpox, this vaccine led to the development of future ones.


Jenner was born to a wealthy and well-educated family. Like many during his time, he was inoculated for smallpox, a process where a small amount of smallpox scar tissue is put into the upper skin of a person. This process was often either ineffective or, more commonly, caused a mild or full-blown case of smallpox.

Catherine the Great, Tzarina of Russia, famously had herself, her court, and many of her subjects inoculated against smallpox in 1762. Because smallpox killed about 10 percent of the population at this time and maimed countless more, inoculation was considered a reasonable risk.

Vaccine Insight

Jenner realized that people who had suffered cowpox, a similar disease caught from cows, never died and only suffered a mild disease. He theorized that cowpox would bring on smallpox immunity with no chance of suffering smallpox itself. When a milkmaid presented suffering cowpox, he tested his theory by taking an amount from her scar and purposefully infecting his gardener’s son. Later he would inoculate the boy with smallpox and observe the child had none of the normal side effects.

Jenner then purposefully infected the child with smallpox and observed the boy was entirely immune. From this, he gathered that cowpox immunizes against smallpox with no risk of developing smallpox.

Jenner publicized his findings in 1798. He named his process “vaccination” after the Latin name for cow, Vacca: vaccine referred to the medicine. Jenner received countless awards from around both Great Britain and the world. The British government awarded him £10,000 in 1802 and another £20,000 in 1807.

Louis Pasteur would later go on to create a vaccine for anthrax.

Inoculation dates to about 1000 BCE from China.