Henry Oldenburg wrote Letter L-052 to Leeuwenhoek for more details about his method for observing little animals

February 22, 1677

Written on February 12 O.S. in London.

This letter is known only by reference in other letters.

In the two letters that he dated the 12th and 22nd of February 1677 O.S., Henry Oldenburg wrote to Leeuwenhoek that his observations of microbes in water (Letter L-040 of 9 October 1676) were well received by the members of the Royal Society, although they find it hard to conceive of the number of little animals that Leeuwenhoek claimed to have seen. They also asked Leeuwenhoek to further study muscles and brains. Oldenburg also passed along the greetings of Robert Boyle and Nehemiah Grew.

Prompted by Oldenburg, in Letter L-054 of 23 March 1677, Leeuwenhoek explained his method for calculating the number of little animals. In Letter L-056 of 14 May 1677, Leeuwenhoek further examined muscles and brains, as the members of the Royal Society had requested.

This letter is calendared as Letter 3060 in Hall and Hall, The Correspondence of Henry Oldenburg, vol. XIII, July 1676 – July 1681, p. 211.


Letter L-054 of 23 March 1677 to Henry Oldenburg responded to two of Oldenburg’s letters at the same time:

I received your welcome letters of the 12th and 22th of the last month; and I was not a little pleased to see that Mr. Boyle and Mr. Grew sent me their remembrances. Pray give them my respectful compliments. I was also pleased to see that my observations about water etc. had not displeased your learned philosophers. Nor do I wonder, they could not well apprehend how I had been able to observe so vast a number of living creatures in one drop of water, that being very hard to conceive without an ocular inspection. Meantime, I never affirmed that there are so many of these animals in this water, but I generally said that I imagined I saw so many. ...

As regards the request of your good friends concerning the fleshy fibres of the muscles and the cortex and the medullary parts of the brain, I have observed these on several occasions, but I shall take the first opportunity to examine them again sedulously, and will then send you my observations on that subject.

Letter L-056 of 14 May 1677 to Henry Oldenburg

Yours of the 22th of February mentions that some of your good friends did wish, I would with all possible exactness observe the carneous fibres of a muscle (fibras carneas musculorum animalis) and also the cortical and medullar part of the brain (corticem et medullam cerebri).

“I acquainted you formerly in my letter of the first of June 1674, that those carneous fibres of muscles did consist of very small globuls; yet for the further satisfaction of your friends, I have laid aside all my former observations, to make quite new ones.