Metchnikoff originated the theory of phagocytosis. He described phagocytes in leucocytes and showed their function as scavengers. Abridged English translation in Bibel, Milestones in immunology (1988).

Metchnikoff delivered his classic lectures on inflammation in French at the Pasteur Institute. They were translated into Russian as Lektsii o sravnitelnoi patologii vospaleniy, and published in St. Petersburg by K. L. Rikker in 1892. The lectures were translated into English from the French by F.A. Starling and E. H. Starling as Lectures on the comparative pathology of inflammation, and published in London in 1893, Digital facsimile of the original French edition from the Internet Archive at this link. Digital facsimile of the English translation from the Internet Archive at this link.

See No. 2538

A classic study of the mechanisms concerned in specific antibacterial immunity, and one of Metchnikoff’s best works.  Russian edition: Nevospriimchivost’ k infekcionnim boleznyam. St. Petersburg: K.L. Rikker, 1903. English translation, London, 1905. Digital facsimile of 1901 edition from bnf.gallica at this link.

In 1908 Metchikoff shared the Nobel Prize in Physiology or Medicine with Paul Ehrlich "in recognition of their work on immunity." See also Nos. 2307 and 2538.

Metchnikoff and Roux successfully transmitted syphilis from man to the higher apes. Although not the first to do this, they recorded much new information concerning the disease.

Metchnikoff researched the effect of lactic acid produced by Lactobacilli on other non-desirable bacteria in the digestive tract. He thus expanded Döderlein's (No. 6279) concept of "normal flora" beyond the vagina.

Translated into English as Notes on soured milk, and other methods of administering selected lactic germs in intestinal bacterio-therapy. London: John Bale, Sons & Danielsson, 1909.

For what he called bacterio-therapy, Metchnikoff recommended eating yogurt. From p. 20: "The inexperienced reader may be surprised at our suggesting the ingestion of large quantities of microbes, the popular idea being that microbes are necessarily injurious. This view, however, is altogether erroneous; for there are many useful microbes, and among them the lactic organism occupies a foremost place."

(Thanks to Juan Weiss for the reference to the English translation and its interpretation.)