Yes, you read that right, poisonous cheese. When I was perusing the Michigan Department of Public Health Report for 1885 for my article about diphtheria, I stopped short. Poisonous cheese? Really, I thought? OK, I'll bite, well, actually read. I certainly didn't expect to spend nearly an hour scouring Google for references to poisonous cheese and Victor Vaughan who did the original experiments.
Let me back up. Within thirteen months in 1883-1884, eight outbreaks of illness (in several localities throughout Michigan) were linked to consumption of tainted cheese. Those afflicted ate the cheese and within hours were overcome by nausea, vomiting and diarrhea. Over two hundred people had been sickened and while a few were considered close to death, all apparently recovered within a matter of days.  The State Department of Health decided to look into the issue. Samples of tainted cheeses were sent to two doctors, George Sternberg (U.S. Army) and Victor Vaughan (University of Michigan). Sternberg fed portions of the cheeses or extracts thereof to a number of types of animals, all without any effect, though when Sternberg's assistant consumed a small portion of the cheese he experienced nausea, vomiting and diarrhea. Sternberg also examined liquid from cavities within the cheeses under the microscope and found micrococci. In his letter to the the Board of Health he regretted that as he had found no toxic effect in the animals and was swamped with work that he could not devote additional efforts to the investigation. 
Victor Vaughan, however, kept at his work and was rewarded for his diligence. Vaughan began trying to extract the toxin from the cheese. Eventually, he settled on an ether extraction method and produced crystals of what he called tyrotoxicon (from the Greek for “cheese poison”). When one of these crystals was placed upon the tongue, “a very sharp, burning sensation” and nausea immediately resulted. “A drop of the fluid in which the crystals formed, placed on the tongue, produced, in addition to the symptoms mentioned above, gripping pains in the bowels, followed by one or more diarrheal discharges.” He determined that tyrotoxicon belonged to the chemical class of poisons known as ptomaines. Ptomaines “originate in organic substances which are undergoing putrefactive changes.”  Dr. Vaughan believed that tyrotoxicon was likely the product of bacterial action. Vaughan's accomplishment may not sound like much to us, but it seems to have been ground-breaking. I found references to his findings in newpapers as far distant as Australia.
All of the poisonous cheeses instantly reddened blue litmus paper (indicating the presence of a strong acid), while good cheese did not. Vaughan advised grocers to apply the litmus test to all cheeses upon cutting a new cake to avoid selling a poisonous one. Vaughan also advised additional precautions to avoid the contamination of milk. Besides providing the cows with clean forage and fresh water he recommended washing the udders prior to milking and importantly, stressed that milk should be immediately cooled thoroughly. He further suggested that vessels in which milk were kept should be regularly cleaned, scalded and dried before being reused. 
Vaughan later came to believe that cholera infantum, which exhibits symptoms nearly identical to those of cheese poisoning could be caused by the same agent and found in contaminated milk or on contaminated and improperly cleaned baby bottles. The reason that the infants often died was because milk was their primary or sole food source and because infants are by nature more susceptible to disease. Later, Vaughan was to conclude that several different microorganisms could be the cause of cholera infantum. 
Vaughan's interest in “sanitary matters” had led him to the forefront of bacteriology. He actually spent the summer of 1888 training in Robert Koch's laboratory in Berlin.  Vaughan truly had an illustrious career, working with Walter Reed to examine typhoid fever during the Spanish-American war and eventually serving as president of the American Medical Association. It is amazing what the study of a few hundred cases of poisonous cheese can lead to.
- Twelfth Annual Report of the Secretary of the State Board of Health, of the State of Michigan for the Fiscal Year Ending Sept. 30, 1884. 1885. W.S. George & Co., State Printers and Binders. Lansing, Michigan.
- Thirteenth Annual Report of the Secretary of the State Board of Health, of the State of Michigan for the Fiscal Year Ending Sept. 30, 1885. 1886. Thorp & Godfrey, State Printers and Binders. Lansing, Michigan.
- First Annual Report of the State Dairy and Food Commissioner of Wisconsin. 1890. Democrat Printing Company, State Printer. Madison, Wisconsin.
- Vaughan, V.C. and Novy, F.G. Cellular Toxins or the Chemical Factors in the Causation of Disease. 1902. Lea Brothers & Co. Philadelphia and New York. P93
- Victor Clarence Vaughan. American Journal of Public Health and the Nations Health: January 1930, Vol. 20(1), pp. 53-55.