SOURED MILK FERMENTED WITH LACTIC-ACID BACTERIA ('BULGARIAN BACILLUS')

animal tissue

provenance:animal tissue

first introduced:1907

regulatory status:unregulated

context:Soured milk fermented with lactic-acid bacteria is an ancient food; its promotion as a life-extending therapy dates from Metchnikoff's *Essais optimistes* (1907) and the 1908 English translation *The Prolongation of Life*. The active organism Metchnikoff promoted was the 'Bulgarian bacillus,' isolated from yahourth (Bulgarian soured milk) and studied at the Pasteur Institute. The bacillus had been described in 1905 by Stamen Grigorov (rendered 'Grigoroff' in Metchnikoff's 1908 text), a Bulgarian student working in the Geneva laboratory of Professor Léon Massol. The yogurt organism is classified today as *Lactobacillus delbrueckii* subsp. *bulgaricus*.

MECHANISM CLAIMED

Lactic-acid bacteria introduced into the gut via soured milk produce lactic acid (and, per Metchnikoff's account of Belonowsky's work, a further antiseptic substance) that arrests the putrefactive fermentation of the large intestine. By suppressing the putrefactive microbes whose toxins Metchnikoff held responsible for arteriosclerosis and senility, daily consumption was claimed to delay aging and prolong life.

MECHANISM ACTUAL

*Lactobacillus delbrueckii* subsp. *bulgaricus* is the standard yogurt organism and is relatively acid-sensitive compared with some other lactobacilli; ingested yogurt bacteria can survive gastrointestinal transit and be recovered in feces, but there is no evidence that the Bulgarian bacillus permanently colonizes or establishes in the human large intestine. The wider theory the ingredient was meant to serve, intestinal autointoxication, was discredited in the early 20th century: putrefactive products are not absorbed from the gut in the harmful quantities the theory required. The food-preservation analogy (lactic fermentation preserves meat and silage) does not establish any effect on human lifespan, and no controlled human outcome data supported the life-extension claim.

INTERVENTIONS USING IT

Soured-milk ('Bulgarian bacillus') longevity therapy

NOTES

Soured milk fermented with lactic-acid bacteria was the active material of Metchnikoff’s longevity programme. The provenance field is encoded as animal_tissue because this is the closest available match in the v0 schema: the preparation is a fermented mammalian-milk product, and the schema has no microbial or fermented-food category. The biologically operative agent is not the milk itself but the live lactic-acid bacteria it carries, principally the ‘Bulgarian bacillus’ (now Lactobacillus delbrueckii subsp. bulgaricus), described by Grigorov in 1905 and adopted by Metchnikoff as the agent best suited to displace the putrefactive flora of the colon. The mechanism Metchnikoff claimed (lactic acid and a secreted antiseptic arresting intestinal putrefaction, and thereby aging) rests on a food-preservation analogy and on animal experiments rather than on controlled human outcome data. Modern work finds transient gut passage but no permanent colonization, and the autointoxication theory the ingredient was meant to serve did not survive empirical scrutiny.