The writer was a supporter of his "religion", which implied the need for spiritual self-purification and improvement, which could give a person longevity.
From his materialistic point of view, Mechnikov argued for the need to adhere to the correct way of life, significantly extending human life.
The main research laboratory Mechnikov made his body. He first thought about it when his young wife was dying. She had typhoid, and doctors told me to prepare for the worst. Ilya was in despair: several years ago he buried the first wife who died of tuberculosis, even tried to commit suicide, but failed. And now the test fell to his share a second time. He decided to die with his beloved: he introduced himself into the blood of the bacteria that cause typhoid. He fell ill, but in a strange way he soon recovered with his wife. After that, the scientist decided to no longer play with life in such games.
Ilya Mechnikov made many discoveries in the field of immunology, microbiology, embryology, in 1908 he received the Nobel Prize for the phagocytic theory of immunity. Subsequently, he actively engaged in the study of aging and became one of the founders of gerontology - the science of aging and death of the organism. He also introduced the term "orthobiosis" into science, which means the correct way of life (from the words "orto" - correct and "bio" - life).
The biologist often asked the question: why do people fear death? And he came to the conclusion: the reason is that life is too short, and the person does not have time to get enough of it. He gave an example of how long-livers die - in good old age and with the calm feeling that earthly life is complete. He began work on the theory of the prolongation of life, the main points of which were expounded in such works as “Studies on the Nature of Man” (1903) and “Studies of Optimism” (1907). The brevity of the physical life and the desire to live longer, he called the main disharmony of human nature. He wrote that the task of future generations will be the search for ways to prolong life, so that a person can achieve a natural completion of the life cycle and have time to get enough of it.
Conducting research on the number of centenarians in different countries, the scientist made the discovery that Bulgaria is leading the list (4 per 1000 people). In 1908 he published an article “A Few Words about Sour Milk,” in which he argued that old age occurs as a result of self-poisoning by organisms with poisons and waste products of microorganisms, as well as elements of the organism itself. Poisoning occurs as a result of poor nutrition and excessive consumption of meat products.
In order to slow down the aging process, it is necessary to pay attention to the intestinal microflora. The scientist made a sensational statement, declaring the large intestine atavism and the main cause of poisoning of the body. At the dawn of human development, the intestine served as an organ for the processing of coarse plant food, but with the development of civilization it became the source of the development of putrefactive bacteria. But since it is impossible to remove the intestines, it is necessary to introduce an antagonist of Escherichia coli — lactic acid bacteria — that normalize digestion.
He actively promoted the use of yogurt on the basis of the Bulgarian lactic acid bacillus (in Bulgarian, “Kiselo mlyako”), which he called the “elixir of immortality”. We now call this product yogurt, although it is often prepared using a different technology. By the way, the Bulgarians are trying in every way to protect their national product from fakes.
Followers of scientists developed the Mechnikov's theory of gerontology, currently more than 10,000 works on this topic are published annually. Many researchers do not consider Mechnikov’s theory true and call other causes of aging — for example, cell damage by free radicals. Nevertheless, everyone agrees that the healthy microflora of our intestines is the key to good health.
So how did the discussion of Tolstoy and Mechnikov end? It was impossible to convince Lev Nikolayevich, although, as he said goodbye, he said: "I drink your yogurt and promise to live up to a hundred years."