The first probiotic to ever be known to science was a certain strain of a bacillus – a rod-shaped bacteria that is a member of the Firmicutes phylum - in a type of Bulgarian yoghurt. This probiotic was named Lactobacillus bulgaricus to reflect the fact that it was first found in Eastern European yoghurt. A physician and microbiologist named Stamen Grigorov was credited with the discovery when it was first made in 1905. The Bulgarian scientist merely noted the existence of this bacillus, however, and did not go on to theorise greatly on the existence of others and what they might be doing in the guts of human beings. The modern-day theory that is based on his initial discovery is generally attributed to Élie Metchnikoff, a Nobel laureate who gained his prize for his work on immunity. It was the Russian-born Metchnikoff who first came up with the idea that Bulgarian peasants, who consumed their local yoghurt in great quantities throughout their lives, tended to live longer lives than other comparable communities.