The number of centenarians among Bulgarian peasants is attributable to their consumption of soured milk (yahourth) containing lactic-acid bacteria.
This is the observational support Metchnikoff offered for the sour-milk programme. In The Prolongation of Life (1908) he reports M. Grigoroff’s surprise at the number of centenarians in Bulgaria, a region where soured milk is a staple food, and treats the association as evidence for the protective action of lactic-acid bacteria. The endpoint is testimonial: an uncontrolled population observation with no verified vital-statistics base and no control for confounders (diet, activity, age misreporting in rural populations). It is classified as unreplicated because the asserted causal link between Bulgarian milk consumption and exceptional longevity was never established by controlled study; Podolsky (1998) treats the longevity attribution as part of the theory’s rhetorical appeal rather than a demonstrated fact.
Appears in
Sources
- The Prolongation of Life: Optimistic Studies — Metchnikoff, Élie. *The Prolongation of Life: Optimistic Studies*. English translation by P. Chalmers Mitchell. New York and London: G.P. Putnam's Sons, 1908. (French original: *Essais optimistes*, Paris: A. Maloine, 1907.)
- Cultural divergence: Elie Metchnikoff's Bacillus bulgaricus therapy and his underlying concept of health — Podolsky SH. 'Cultural divergence: Elie Metchnikoff's *Bacillus bulgaricus* therapy and his underlying concept of health.' *Bulletin of the History of Medicine* 1998;72(1):1-27. PubMed: 9553272.