Metchnikoff was also greatly encouraged by Virchow, who happened to pass through Messina and came to see his preparations and his experiments, which seemed to him conclusive. However, Virchow advised him to proceed with the greatest prudence in their interpretation, as, he said, the theory of inflammation admitted in contemporary medicine was exactly contrary to Metchnikoff’s. It was believed that the leucocytes, far from destroying microbes, spread them by carrying them and by forming a medium favourable to their growth.
Metchnikoff always preserved a deep gratitude towards Virchow and Kleinenberg for the moral support which they gave him at that time.
When the hot weather came, we left Messina for Riva, a delicious summer resort on the shores of the Lake of Garda. There, Metchnikoff wrote his first memoir on the reaction of inflammation and on the digestion of microbes by the mesodermic cells of lower invertebrates. On the way back to Russia through Vienna, he went to see the Professor of Zoology, Claus; he found other colleagues with him and expounded his theory to them. They were much interested, and he asked them for a Greek translation of the words “devouring cells,” and that is how they were given the name of phagocytes.
Claus asked him for his memoir for the Review which he edited and in which it appeared soon afterwards, in 1883.[16] The new-born “phagocyte theory” was thus very well received by naturalists and by Virchow, the father of cellular pathology.
Having returned to Russia, we went to the country, where Elie had to attend to family business; nevertheless, he continued his researches in every leisure moment. He had observed in Echinoderma that, during the transformation of their larvæ, the parts becoming atrophied were englobed by mesodermic mobile cells. In those observations he was delighted to have found an example of physiological inflammation, i.e. one which presented itself in normal and non-morbid conditions. He thought he might observe it also during the metamorphosis of the tadpole into a frog, whilst the tail was being atrophied. But he found that, instead of the leucocytes of the blood, certain cells from the muscular tissue were those which devoured the enfeebled elements of the tail; he thus learnt that phagocytes might be, not only the white blood corpuscles, but other cells of mesodermic origin.[17]
In autumn 1883 he read his first paper on phagocytosis to a congress of physicians and naturalists at Odessa.[18] He compared the phagocytes to an army hurling itself upon the enemy and looked upon the phagocytic reaction as a defensive force of the organism.
In that paper itself and from that moment onwards, the trend of his ideas towards optimism becomes visible. By discovering the phagocytic reaction of the organism, he made a first breach in his philosophy of human nature, hitherto so pessimistic; he discovered within it a salutary element which could be utilised by science to combat its discords. He began to have some faith in the power of knowledge, not only for this struggle, but also for the establishment of a rational conception of life in general. Thus he said in his paper to the Odessa Congress:
The theoretical study of Natural History problems (in the largest sense of the word) alone can provide a critical method for the comprehension of truth and lead to a definite conception of life, or at least allow us to approach one.
And yet, until then, the theory of phagocytosis as a curative force of the organism was but a hypothesis, for he had not yet observed spontaneous phagocytosis in diseases and did not know pathogenic microbes. He therefore sought to study them in lower animals, whose simple structure made the observation easier. He found some small, transparent, fresh-water crustaceans, called daphniæ, which were diseased and easy to place alive under a microscope. These crustaceans are often infected by a parasite fungus (Monospora bicuspidata), of which the spores, shaped like sharp needles, are introduced with food into the digestive tube, traverse the walls of it, and thus penetrate into the general cavity of the body. They are immediately attacked by mobile phagocytes, which either singly or in groups englobe them; if the phagocytes succeed in digesting the spores, the daphnia recovers; in the contrary case, the spores germinate and develop into small fungi which invade the organism and kill it. The recovery or death of the daphnia depends therefore on the issue of the struggle.[19] This observation gave final confirmation to the hypothesis of the curative forces of the organism.