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It is named after John Langdon Down, the British doctor who fully described the syndrome in 1866. Some aspects of the condition were described earlier by Jean-Ãtienne Dominique Esquirol in 1838 and Ãdouard SÃ©guin in 1844. In 1957, the genetic cause of Down syndrome, an extra copy of chromosome 21, was discovered.
Conservation of mass. Russian scientist Mikhail Lomonosov discovered the law of mass conservation in 1756 by experiments, and came to the conclusion that phlogiston theory is incorrect. Antoine Lavoisier's discovery of the Law of Conservation of Mass led to many new findings in the 19th century.