Mycobacterium tuberculosis strain H37Rv is the most studied strain of tuberculosis in research laboratories. It was first isolated by Dr. Edward R. Baldwin in 1905. The strain came from a 19 year old patient with chronic pulmonary tuberculosis at the Trudeau Sanatorium in Saranac Lake, New York. It was maintained for many years by serial passage of cultures at the Trudeau Sanatorium and initially named strain H37. Over time it was found to have variable virulence in animal models based on which medium it was grown on. Strains with different virulence were then intentionally produced, with H37R being less virulent after growing in acidic media and H37S was more virulent in guinea pigs after being grown in alkaline media. The more virulent strain was later renamed H37Rv, with R standing for rough morphology and v standing for virulent. The strain was used for many laboratory studies and became the standard for tuberculosis. It was later designated as the neotype for the species.