Elie Metchnikoff's Metamorphosis Essay

Elie Metchnikoff has discovered phagocytosis in a starfish. The inner space of starfish is a primitive version of human extravascular (extravasal) compartment. The first line of host defense in humans is extravascular compartment which is evolutionally older than intravascular compartment (cardiovascular and lymphatic systems) and includes external and internal covers (skin, conjunctiva, tympanum, upper and lower respiratory mucous membranes, digestive tract mucous membranes, etc.) and different organs and structures (the brain, internal and endocrine organs, muscles, red bone marrow). Some organs and tissues are in direct contact with the environment (the lungs, the skin, gastrointestinal epithelium, etc.), the others are internally located (the brain and spinal cord, the liver, the kidneys, endocrine glands, testes and ovaries) and have no direct contacts with the environment. The cardiovascular system
Stinging, biting and wounding in the nature are the equivalents of subcutaneous, intradermal, or intramuscular injections of venoms, poisons, bioactive substances and infection materials. Insects (mosquitos, flies, fleas, chiggers, ticks, lice, etc.) have always been the vectors of infections: plague, malaria, filariasis, leishmaniasis, trypanosomiasis, spotted fever, borreliosis, tularemia, babesiosis, viral encephalitis and many others. They introduce the bacterial, viral and protozoan pathogens to human skin – the cover of extravascular compartment. The history of vaccination also is the history of inoculating infectious materials to extravascular compartment. Pulmonary, gastrointestinal and urogenital infections have been entering the human body through the extravascular compartment as