Summary

Élie Metchnikoff argues that human lifespan can be significantly extended by combating intestinal autointoxication—the poisoning of the body by putrefactive bacteria in the large intestine. He proposes that the key to prolonging life lies in replacing harmful gut microbes with beneficial lactic acid bacteria, such as those found in fermented milk products like yogurt. Metchnikoff also contends that aging is a preventable disease caused by chronic inflammation and cellular degeneration, not an inevitable biological fate. The book synthesizes his research on phagocytes (immune cells) with dietary interventions, advocating for a hygienic lifestyle that includes sour milk consumption, avoidance of overeating, and mental optimism. Readers take away a pioneering vision of gerontology rooted in microbiology, where diet and microbial balance directly influence longevity.

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Key concepts

Intestinal autointoxication — The theory that toxic byproducts from putrefactive bacteria in the colon accelerate aging and disease.
Lactic acid bacilli — Beneficial bacteria (e.g., *Lactobacillus bulgaricus*) that suppress harmful gut flora and are introduced via fermented dairy.
Phagocytosis — The process by which white blood cells engulf pathogens, central to Metchnikoff’s Nobel-winning work on immunity.
Orthobiosis — Metchnikoff’s term for the correct, healthful way of living that aligns with natural biological processes to extend life.
Senescence as disease — The idea that aging is a pathological condition caused by chronic inflammation and microbial toxins, not a natural limit.