Ilya Mechnikov

Observing mobile cells in starfish larvae at Messina in 1883, he proposed that such cells defend the body by engulfing intruders and named the process phagocytosis, founding the cellular theory of immunity.

From 1888 he worked at the Pasteur Institute in Paris, where he defended the cellular theory against the humoral school of Behring and Ehrlich, and with Emile Roux showed that syphilis can be transmitted to monkeys; in 1908 he shared the Nobel Prize in Physiology or Medicine with Ehrlich.

In later years he studied the intestinal flora and proposed that fermented milk could slow senility; the effect was never validated, but reviewers see the idea as a forerunner of probiotics and microbiome research.

To test his idea that mobile cells defend the body, he pushed thorns from a tangerine tree into transparent starfish larvae and found them surrounded by cells the next morning.

This is consistent with a habit of turning an idea into a direct, simple experiment. Experimentation

Virchow, after seeing his preparations at Messina, warned him that the accepted theory of inflammation was the opposite of his; he kept developing the phagocyte theory and defended it against Koch, Behring and others for about twenty-five years.

This is consistent with sticking to an evidence-based view against the prevailing consensus. Independent Thinking

After resigning from the University of Odessa in 1882 he worked in a private laboratory at Messina, where his observations moved him from zoology and embryology to pathology and immunity.

This is consistent with an ability to redirect a career into a new field when a discovery opens it. Cross-Domain Range