In the early 1900s, the Bulgarian scientist, Dr. Stamen Grigorov, found the specific Lactobacillus bacteria responsible for Bulgarian yogurt fermentation. Grigorov went on to identify two more bacteria: Streptobacillus and Streptoccus thermophilus, which coexisted with Lactobacillus in perfect symbiosis. He also found that these two bacteria are not part of human intestinal micro-flora, but are very beneficial when introduced to it.