However, he ascertained that it is not only the food diet which regulates the quantity of microbian poisons contained in the organism; that quantity sometimes varies very much in spite of an identical diet. He thought that a very important part of influence is due to pre-existing microbes which prevent or favour the development of microbes of putrefaction. All these questions, complicated by the richness and variety of the intestinal flora, still demanded a long series of laborious researches.
At the end of the winter he felt tired, and we went to the seaside during the holidays. But the sharp sea air did not suit him; he had a beginning of cardiac asthma and nearly fainted during a walk. We therefore had to come away from the sea, and went inland, to Eu. At the beginning of our stay, Metchnikoff did not feel well, walking tired him, he suffered from cardiac intermittence; it was only gradually that his condition improved and he was able to write the preface to a Russian edition of his philosophical articles.
This book was entitled Forty Years’ Search for a Rational Conception of Life, and the articles record the evolution of his ideas and his search “not only for a rational understanding of life, but also for the solution of the problem of death, which is so full of contradictions.”
This collection of articles enables us at the same time to follow the gradual transition from the pessimism of his youth to the optimism of his maturity. His first writings[28] relate to the discords of human nature and the lack of a solid basis for morals.
But, already in 1883, he concluded an opening Causerie at the Naturalists’ Congress in Odessa, by the following words: “The theoretical study of natural history problems, in the widest sense of the word, alone can give a sound method for the comprehension of truth and lead to a definite conception of life—or at least to an approach to it.”
Another article, The Curative Forces of the Organism, sums up his phagocyte theory, and states the fact that the organism possesses special powers of struggle against enemy elements.
In 1891, he wrote The Law of Life, in which we find the dawning idea that the lack of harmony in human structure does not make a happy existence and a rational code of morals impossible. Morals must consist “not in rules of conduct adapted to our present defective human nature, but on conduct based upon human nature modified, according to the ideal of human happiness.”
The Flora of the Human Body, published in 1901, is a study in which Metchnikoff’s optimism assumes a definite form, for he speaks of the efficacy of certain means of struggling with our lack of harmony.
The last chapter in the book, “A Conception of Life and of Medical Science,” introducing the word Orthobiosis, strikes the optimistic chord, winged and conclusive, which must result from victory over the disharmonies of human nature. This is Metchnikoff’s ultimate formula, summing up the problems of life and of morals: