1676: I discovered living creatures

In 1676, Leeuwenhoek wrote ten letters, all but two to Henry Oldenburg. One went directly to Robert Boyle. Another, to Constantijn Huygens, contained an excerpt from the letter of October 9.

The letters before October 9 are dominated by Leeuwenhoek's detailed written responses to Johan van Beverwijck, Nehemiah Grew, and Robert Boyle.

Leeuwenhoek had a busy summer in 1676, making daily observations of water from various sources to learn when and under what conditions the little animals appeared. Where did they come from? How many were there? How long did they live? The result was the letter of October 9, which presented a convincing amount of evidence for the microbial world only he had explored, somewhere between Columbus and Adam.


Leeuwenhoek wrote in yet another letter unpublished during his lifetime, dated January 22 (AB 20), about his difficulties finding someone in Delft to translate Oldenburg's letters and Philosophical Transactions articles into Dutch. He gave instructions to have packets of Philosophical Transactions issues sent via his sister "Catatarina" (Catharina) in Rotterdam. He added (my translation and emphasis):

De levende schepselen int water bij mij ontdeckt is ordinair Hemelwater dat vande pannedacken in steene backen onder de aerde ofte in tonnen gevangen wort, alsmede in het put off bornwater dat uijt het wel-sant opcomt, jtem in het gracht water dat door dese stadt en door het lant loopt, hier van heb ick verscheijde aenteijckeningen gedaen, soo van haer courluer, gedaente, de delen waer uijt haer lichaem is te samen gestelt, bewegingh, en schielijcke verbrijselingh van haer gantsche lichaem.

The living creatures in water discovered by me in ordinary rainwater that was collected from the tile roofs in stone cisterns below the ground or in barrels, as well as in well water that rises out of the sand, also in the canal water that runs through this city and through the country, hereof have I made various notes, so of their color, shape, the parts of their bodies is composed, the movements, and the sudden shattering of their whole body.

Those notes ended up in the long letter dated October 9, the one that made him famous.


His next letter, dated February 22 (AB 21), also unpublished, is full of observations about hair, horn, and bone. Leeuwenhoek wrote to Oldenburg:

I learned that Mr. Hooke spoke about the hair to you. I shall be pleased to learn about our differences. When I shall be better informed I am quite willing to give up my opinion and accept Mr. Hooke's view. Please give him my best regards.

He spends the second half of this long letter refuting Johan van Beverwijck on the characteristics of hair. In closing, he write

Sir, originally I had the intention to tell you of the living creatures in water ... But in order not to make this letter too long I will stop and remain, ...

For the second letter in a row, he brought up the living creature. Perhaps his initial observations raised too many unanswered questions. Within a month, he began a summer-long process of finding out. First, he had to respond to Nehemiah Grew.


His next letter, dated April 21 (AB 22), was the only one published in volume 11 of Philosophical Transactions. He presented his observations about the vascular system of a thin section of a year-old sprig from an ash tree.

Monsieur Constantin Huygens of Zulichem was pleased to shew me the Comparative Anatomy of the Trunks of Plants, written by Doctor Grew, and told me, that he had very ingeniously and learnedly discoursed upon that subject; though I, by reason of my unskilfulness in the English Tongue, could have little more than the contentment of viewing the elegant Cuts.

Leeuwenhoek followed with over two pages explaining his diagram (see left; click to enlarge), often comparing his observations to Grew's explicitly nd implicitly. He ended:

I beg your favour, Sir, to communicate this to Dr. Grew, with my service to him, and to inquire of him, whether he hath seen as well as I. ... An answer to which particulars I should be very glad to receive from the said Doctor.

When published in the July 18 number of Philosophical Transactions, Leeuwenhoek's explanation had twenty-seven numbered references within it, added by Grew, who supplied the Notes after Leeuwenhoek's letter. The notes, running half again as long as Leeuwenhoek's original description, respond in great detail, sometimes confirming, sometimes contradicting. While such detailed responses were common during meetings of the Society, I can find no other instance in the early Philosophical Transactions of an article with a detailed point-by-point response immediately following it.

At the end of the letter, between his observations of the ash sprig and Grew's response, is a paragraph about "some French Wine, ... which hath a very delicate taste." Leeuwenhoek continued:

In this wine I have divers times observed small living Creatures, shaped like little Eels. ... These creatures I have kept in my Study for a whole month swimming in Wine. And though they move strongly, yet they make but little way, whereof the cause may be, that they are quite destitute of leggs.

Grew's response was all about the ash sprig, nothing about the "small living Creatures".