Ilya Ilyich Mechnikov was born on May 16, 1845, in a village near Kharkoff in Russia. He was the son of an officer of the Imperial Guard, who was a landowner in the Ukraine steppes. His mother, née Nevakhowitch, was of Jewish origin.

         Mechnikov went to school at Kharkoff and was, even when he was a little boy, passionately interested in natural history, on which he used to give lectures to his small brothers and to other children. He was at that time especially interested in botany and geology. When he left school he went to the University of Kharkoff to study natural sciences, and worked there so hard that he was able to complete the four year course in two years. Graduating at Kharkoff, he went, first to study marine fauna at Heligoland, and then to the University of Giessen, where he worked under Leuckart. Subsequently he went to the University of Göttingen and the Munich Academy, where he worked in von Siebold's laboratory. While he was at Giessen, he discovered, in 1865, intracellular digestion in one of the flatworms, an observation which was to influence his later discoveries. At Naples he prepared a thesis for his Doctorate on the embryonic development of the cuttle-fish Sepiola and the Crustacean Nelalia.

        In 1867 he returned to Russia, having been appointed docent at the new University of Odessa and from there he went to take up a similar appointment at the University of St. Petersburg. But in 1870 he was appointed Titular Professor of Zoology and Comparative Anatomy at the University of Odessa.

        At St. Petersburg he met his first wife, Ludmilla Feodorovitch, who suffered from tuberculosis so severe that she had to be carried to church in a chair for the wedding. For five years Mechnikov did all he could to save her life, but she died on April 20, 1873. Broken by this loss, troubled by weak eyesight and heart troubles and by difficulties in the University, Mechnikov became, at this time, so pessimistic that he tried to take his own life by swallowing a large dose of opium; but, fortunately for himself and for the world, he did not die. It was in Odessa, in fact, that he met his second wife, Olga, whom he married in 1875. In 1880 his second wife had a severe attack of typhoid fever and, although she did not die, Mechnikov, whose health was still poor, again tried to take his own life. This time, however, he decided, in order to save his wife and others embarrassment, to do this by means of the scientific experiment of inoculating himself with relapsing fever to find out whether it was transmissible by the blood. The attack of relapsing fever that followed was severe, but it did not kill him.

         In 1882, after his recovery from this disease, Mechnikov resigned his appointment at Odessa because of difficulties in the University during the period of reactionary government which followed the assassination of Alexander II.

        He then went to Messina to continue, in a private laboratory he set up there; his work on comparative embryology, and it was here that he discovered the phenomenon of phagocytosis with which his name will always be associated. This discovery was made when Mechnikov observed, in the larvae of starfishes, mobile cells which might, he thought, serve as part of the defences of these organisms and, to test this idea, he introduced into them small thorns from a tangerine tree which had been prepared as a Christmas tree for his children. Next morning he found the thorns surrounded by the mobile cells, and, knowing that, when inflammation occurs in animals which have a blood vascular system, leucocytes escape from their blood vessels, it occurred to him that these leucocytes might take up and digest bacteria that get into the body.

        Returning to Odessa, Mechnikov visited Vienna on the way and explained his ideas to Claus, Professor of Zoology there and it was Claus who suggested the term phagocyte for the mobile cells which act in this way. Ultimately in 1883, Mechnikov gave, at Odessa, his first paper on phagocytosis. Apart from its fundamental importance in immunology, the discovery had a marked influence on Mechnikov himself. It completely changed his outlook on life; he abandoned his pessimistic philosophy and determined to find further proof of his hypothesis.

        Some proof of it he found in the small fresh-water Crustacean Daphnia, in which he found that fungal spores which attacked it were themselves attacked by the phagocytes of the crustacean. He then studied anthrax bacilli and found that the more virulent strains of these were not attacked by the phagocytes, while the less virulent strains were.

        During this period Mechnikov had been appointed Director of an Institute established in 1886 in Odessa to carry out Pasteur's vaccine treatment of rabies, but there was much local hostility to this treatment. Mechnikov found that, partly because he was not a medical man, circumstances became so difficult that, in 1888, he left Odessa and went to Paris to ask Pasteur for his advice. Pasteur gave him a laboratory and an appointment in the Pasteur Institute. Here he remained for the rest of his life.

         Apart from his work on phagocytosis, Mechnikov had, during his earlier period of scientific activity, published many papers on the embryology of invertebrates. These included work on the embryology of insects, published in 1866, and, in 1886, his studies of the embryology of Medusae. At the Pasteur Institute in Paris Mechnikov was engaged in work associated with the establishment of his theory of cellular immunity, which, like many great advances in science, encountered considerable hostility. He published, during this period, several papers and two volumes on the comparative pathology of inflammation (1892), and his treatise entitled L'Immunité dans les Maladies Infectieuses (Immunity in infectious diseases, 1901). In 1908 he was awarded, together with Paul Ehrlich, the Nobel Prize for Physiology or Medicine.

        In addition to this work he, together with Roux, proved that syphilis can be transmitted to monkeys. Later he took up the study of the flora of the human intestine and developed a theory that senility is due to poisoning of the body by the products of certain of these bacteria. To prevent the multiplication of these organisms he proposed a diet containing milk fermented by bacilli which produce large amounts of lactic acid and for a time this diet became widely popular.

        Mechnikov received many distinctions, among which were the honorary D. Sc. of the University of Cambridge, the Copley Medal of the Royal Society of which he was a Foreign Member, the honorary memberships of the Academy of Medicine in Paris, and the Academies of Sciences and of Medicine in St. Petersburg. In addition, he was a corresponding member of several other societies and a Foreign Member of the Swedish Medical Society.

      Photographs taken of him when he was working at the Pasteur Institute show him with long hair and an unkempt beard. It is said of him that at this time he usually wore overshoes in all weathers and carried an umbrella, his pockets being overfull with scientific papers, and that he always wore the same hat, and often, when he was excited, sat on it.

      From 1913 onwards Mechnikov began to suffer from heart attacks and, although he rallied for a time and recovered from the distress which the 1914-1918 War caused him, he died on July 16, 1916.

 Extracted from Nobel Lectures,

 Physiology or Medicine 1901-1921.