The Prolongation of Life: Optimistic Studies
period treatise · 1908
LINK
SUMMARY
Metchnikoff's own statement of the sour-milk longevity programme, the central primary source for this case. This is P. Chalmers Mitchell's English translation of the 1907 French *Essais optimistes*. Part II argues that the large intestine harbours putrefactive microbes whose toxic products shorten life, and that deliberately introducing lactic-acid bacteria via soured milk arrests intestinal putrefaction. The chapter 'Lactic Acid as Inhibiting Intestinal Putrefaction' (pp. 161-183 in this edition) sets out the analogy from food preservation to the digestive tube ('As lactic fermentation serves so well to arrest putrefaction in general, why should it not be used for the same purpose within the digestive tube?', p. 166), reports the Pasteur Institute mouse experiments of Dr. Belonowsky on the 'Bulgarian bacillus' isolated from yahourth (soured milk), cites Dr. Herter of New York on intestinal putrefaction in dogs, and records M. Grigoroff's observation of the number of centenarians in Bulgaria, where soured milk is a staple food. The book contains no controlled human outcome data; the longevity case rests on the food-preservation analogy, animal experiments, and population anecdote. Page references in this archive are to the 1908 Putnam edition scanned at archive.org.
NOTES
The Prolongation of Life: Optimistic Studies is the appropriate primary citation for Metchnikoff’s life-extension programme as he stated it. The book extends the argument of his earlier The Nature of Man (English translation 1903) and presents soured milk fermented with lactic-acid bacteria as a practical measure against intestinal putrefaction and the senility he attributed to it. The reasoning is explicit and is reproduced here from the source: lactic fermentation preserves meat, silage, and the must of distilleries from putrefaction, so (by analogy) the introduction of lactic bacilli into the digestive tube should arrest intestinal putrefaction and thereby favour a longer life. The experimental support Metchnikoff cites is animal work (Belonowsky’s mice at the Pasteur Institute; Herter’s dogs) and observational (Grigoroff’s Bulgarian centenarians); no controlled human trial of life extension is reported in the volume. The text is in the public domain and is the source for the verbatim quotations and page references used in this case. Secondary historical assessment is provided by Podolsky (1998) and the modern reassessments by Mackowiak (2013) and by Bested, Logan and Selhub (2013).