One of the great figures of 19th Century biology, Elie Metchnikoff (1845-1916), was a Russian who lived in Paris and did his work at the Instituit Pasteur. He formulated the basic theory on which the science of immunology is founded: that the body is protected from infection by leukocytes that engulf bacteria and other invading organisms. While today we regard this as an obvious and commonplace concept, it certainly wasn't in Metchnikoff's day, and the idea that one cell could "eat" another—Metchnikoff coined the term "phagocytosis" which literally means "the eating of cells"—was very controversial at the time.

As hard as it may be to believe, it was only about 1885 that the "germ theory" of the origins of disease came to be generally accepted by the medical profession, and a lot of needless deaths occurred because of the refusal to accept it. This was especially true in cases of childbirth and amputations, in which nonsterile instruments were frequently used by ignorant surgeons. Even after the concept of infection by germs had finally been proven to be true, the argument that certain cells played an active role in defense against them was even harder for the establishment to swallow. Metchnikoff was widely regarded as a crackpot and lunatic, as had been Pasteur, Lister, and Semmelweiss before him.

The image used in this exercise is a recreation of the experiment Metchnikoff used to prove his theory to be correct. By injecting particulate material into animals he was able to demonstrate clearly and elegantly that phagocytosis really does occur in specialized cells in certain locations. Metchnikoff was later to be awarded the Nobel Prize in Physiology and Medicine, and is today justly considered one of the founding figures of modern medicine.

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