Christiaan Huygens wrote Letter L-205 to Leeuwenhoek, thanking him for the gift of a mangrove tree and inquires whether L.’s observations of the circulation of the blood could also be seen in the wings of bats, the legs of ducks, and the ears of rats

The manuscript is lost. This letter is known only by the summary in Oeuvres complètes. The manuscript of the summary is to be found in the Huygens Collection, University Library, Leiden.

In this letter, Christiaan Huygens thanks Leeuwenhoek for the gift of a mangrove tree and inquires whether Leeuwenhoek’s observations of the circulation of the blood could also be seen in the wings of bats, the legs of ducks, and the ears of rats.

Huygens’s previous letter to L. is Letter L-050 of 9 February 1677. Leeuwenhoek replied to it with two letters, Letter L-051 of 15 February 1677 and Letter L-084 of 15 May 1679 about the ciliar motion of microorganisms. Huygens made no known reply to either letter.

A decade later, Huygens sent the present letter about mangrove trees and blood circulation. There is nothing in any of Leeuwenhoek’s letters about mangroves. However, in Letter L-167 of 17 December 1685, copied in its entirety in Leeuwenhoek’s Letter L-199 of 24 August 1688 to the Royal Society, Constantijn Huygens asks Leeuwenhoek whether he knows anything about root-trees and mentions his son Christiaan. In the previous year, Leeuwenhoek published Letter L-200 of 7 September 1688 separately as Den waaragtigen omloop des bloeds (The true circulation of the blood). It is perhaps to this publication that Huygens is referring. Leeuwenhoek finally replied six months later with his last letter to Huygens, Letter L-207 of October 1689 about some books he sent to Huygens’s father Constantijn Huygens in England.