Reinier de Graaf

Other name: 
Regnier (English), Reijnerus de Graeff (Latinized)
mentor who wrote the cover letter to his first letter to the Royal Society
Birth or Baptism date: 
July 30, 1641
Death or Burial date: 
August 30, 1673

Reinier de Graaf (1641-1673) a physician lived the last ten years of his short life in Delft, where he performed radical, groundbreaking research into human reproduction. He did not use a microscope, but he was the first to develop a syringe to inject dye into human reproductive organs so that he could understand their structure and function.

Several years before Leeuwenhoek remarried (he wrote in 1678 about "nine or ten years" ago), de Graaf showed Leeuwenhoek an experiment to test the hypothesis that blood and milk were the same substance. Leeuwenhoek remembered it this way:

Dr. Graaf opened in my presence the vein of a Dog, and let out so much blood that the Dog grew faint;

Then he opened the Artery of another Dog, and by a pipe transfused the blood of this second into the first, whereby the first was recoverd, the second was faint.

Then the said Doctor injected back into the Artery of the second, a quantity of Cows milk, supposing thereby to preserve the second dog alive, saying, milk was blood: but no sooner was the milk put into the artery, but the dog died.

A few months before his death at 32, de Graaf recommended Leeuwenhoek to Henry Oldenburg, editor of the Philosophical Transactions, a cover letter introducing van Leeuwenhoek addressed to the Royal Society.

That it may be the more evident to you that the humanities and science are not yet banished among us by the clash of arms, I am writing to tell you that a certain most ingenious person here, named Leewenhoek [sic], has devised microscopes which far surpass those which we have hitherto seen, manufactured by Eustacio Divini and others. The enclosed letter from him, wherein he describes certain things which he has observed more accurately than previous authors, will afford you a sample of his work: and if it please you, and you would test the skill of this most diligent man and give him encouragement, then pray send him a letter containing your suggestions, and proposing to him more difficult problems of the same kind.

Oldenburg did exactly as de Graaf suggested.

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