Wrote Letter L-005 of 1674-04-05 to Constantijn Huygens about globules in milk and blood and the growth of hair; first mention of red blood corpuscles

April 5, 1674
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Leeuwenhoek's number: 
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Text of the letter in the original Dutch and in English translation from Alle de Brieven. The Collected Letters at the DBNL - De Digitale Bibliotheek voor de Nederlandse Letteren

Leeuwenhoek wrote this letter to Constantijn Huygens about “globules” in milk and blood; growth of hair. First mention of red blood corpuscles.

Although Malpighi and Swammerdam had observed these structures in blood, Malpighi thought they were fat and Swammerdam didn't pursue them past an initial observation. Leeuwenhoek was the first to recognize what he was seeing, what we now call red blood corpuscles. He kept studying blood, and over the years developed a fuller understanding of it.