Max von Pettenkofer is known as the founder of the discipline of hygiene in Germany. He was well known and highly influential for most of his professional life, much of which was concurrent with the great 19th–century cholera epidemics in Europe. After the mid–1880s, his views on the contagiousness of cholera brought him discredit in the eyes of the international bacteriology community. Pettenkofer believed that cholera was only contagious under certain circumstances. He insisted that the cholera germ, identified by Robert Koch in 1884, required a very specific environment to cause epidemic disease.

Pettenkofer proposed that in order for a cholera epidemic to occur, three factors, which he called X, Y, and Z, were necessary. “X” was the specific pathogen, typically found in the soil. “Y” was the local and seasonal preconditions that allowed the pathogen to transform into a contagious miasma. And “Z” was individual susceptibility to the disease. (When Robert Koch discovered the cholera bacterium in 1884, Pettenkofer said that this germ was the “X” in his theory.) The composition of the soil and its interaction with groundwater was especially important to Pettenkofer’s theory, which is sometimes known as “contingent contagionism” or “localism.”

It was Pettenkofer’s central belief that the cholera germ had to transform or “ferment” under these favorable circumstances before it could become contagious and cause an epidemic. Isolated from these circumstances, the cholera germ could not, in his view, cause disease. Pettenkofer famously demonstrated the strength of this belief in 1892 by drinking a quantity of water infected by pure cultures of the cholera bacillus. Though he did end up getting somewhat ill, he did not develop a full-blown case of cholera.

Pettenkofer’s argument was part of a larger discussion among scientific and medical elites in Europe about contagious disease—in particular, the contagiousness of cholera as epidemics moved from one location to another. The International Sanitary Conferences were convened in part to discuss this issue.

Cholera is a waterborne illness that does not typically spread from person to person by direct contact. A doctor, for example, can treat many cholera patients and never get sick. Anticontagionists typically believed that quarantines were useless against cholera and disrupted trade more than they prevented disease. The British, who controlled trade in many markets, were emphatic in this regard, and went so far as to craft an “official” response refuting Koch’s bacterial theory of cholera transmission, which was published in the Quarterly Journal of Microscopic Science in 1886.

Pettenkofer believed that cholera could be imported through the movement of factor X, and that blocking its movement was much more difficult than altering the predisposing factors Y and Z. Quarantines were also too blunt and all–encompassing to fit well into Pettenkofer’s localist approach. Thus, for the most part, Pettenkofer rejected disinfection and quarantine as being impractical. Instead, he advocated for improving local sanitary conditions as the best way to prevent or stop cholera epidemics.

Pettenkofer’s years of greatest influence were the 1860s and the 1870s. He controlled the Cholera Commission for the German Empire until 1884, when Robert Koch’s discovery of the cholera germ fundamentally altered the terms of the discussion.

Koch was an internationally prominent and influential scientist who held a key government position in a German state that was increasingly inclined to interfere with society. Koch denied that the cholera germ underwent any transformation before becoming contagious, and he asserted that the cholera bacillus was spread most easily through water, not soil.

Koch was a strong supporter of quarantine and disinfection, and his advice on how to prevent cholera was completely different from Pettenkofer’s. His recommendation for the strong state intervention that quarantine and disinfection campaigns required fit well with the German government’s priorities, and Pettenkofer’s localized and individualist approach fell out of favor.