Metchnikoff was not content with observing lower animals but wished to study the reaction of the organism of mammals in infectious diseases. At that time, the best-known microbe was the bacillus of anthrax. He therefore chose that for his researches and ascertained that phagocytosis varied with the virulence of the microbes; thus, while phagocytes did not attack virulent bacteria, they attacked and rapidly digested attenuated bacteria. Moreover, he observed a very active phagocytosis in refractory animals and the reverse in sensitive ones.
He thus came face to face with the question of immunity.
He approached it by a comparative examination of the reaction of the organism of vaccinated rabbits and of non-vaccinated ones, and ascertained that an active phagocytosis was only manifested in a previously vaccinated organism. Metchnikoff explained these facts by the theory that the phagocytes became accustomed, gradually, through vaccination, to strive against more and more virulent microbes.
From that moment, immunity appeared to him as being no other than this progressive hardening. He published his researches in 1884 in Virchow’s Archiv, and impatiently awaited medical reviews, hoping to find some answer, but the memoir passed unnoticed; the full significance of it had not been grasped.
[CHAPTER XIX]
Ill-health of his wife and sister-in-law — Journey to Tangiers through Spain — Villefranche — Baumgarten criticises the phagocyte theory.
In 1884, Metchnikoff’s work was interrupted by the ill-health of my eldest sister and of myself; physicians considered that we had weak lungs and advised that we should spend the winter in the South. Elie, full of anxiety, hastened to take us there.
My younger brothers were now old enough to remain at school in our absence so as to go on with their studies; we therefore started with my two sisters. As cholera was raging in Italy, we went to Spain, hoping to find a place with a mild climate and conditions favourable to my husband’s work. But we traversed the whole country without finding the right combination, and, as we had come too far to go back, we decided to spend the winter on the African coast, at Tangiers, close to Gibraltar where we were.