Wrote Letter 60 of 1687-11-28 (AB 105) to Members of the Royal Society

November 28, 1687
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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.

The original manuscript, written and signed by Leeuwenhoek, is preserved at the Royal Society (MS. 1926. L 2. 17).

Response to other researchers

Leeuwenhoek began this letter by recounting, as he often did, what spurred the investigations he was about to report. In this case, as so often, he was responding to someone else's request.

Mr. Antoni Heinsius, LL. D., Pensionary and Counsellor of this City, one-time Envoy Extraordinary tot His Royal Majesty of France, and then Commissioner of this country to the Court of His Royal Majesty of Great Britain, wrote to me from Westminster on 24th July/3rd August, 1685 that The Right Honourable Robert Boijle would be pleased if I examined, among other things, the cochineal.

I thereupon replied to the abovementioned Mr. Heinsius, on the 10th of August, as follows:

Next came a long passage from his letter to Heinsius followed by Heinsius' reply of August 21/31, reporting Boyle's reaction, again quoted at length.

The question was the origin of cochineal. Was it crushed seeds or crushed insects? After excerpting Heinsius's letter, Leeuwenhoek excerpted his reply to that:

I thereupon wrote to the said Mr. Heinsius, on the 21st September, 1685, as follows with respect to cochineal.

After that long introduction, the reader was caught up and Leeuwenhoek could proceed with his recent observations. He had first seen the cochineal as crushed seeds. Because Boyle disagreed, Leeuwenhoek looked again, and saw that it was crushed shells that also contained other bits of the insect's bodies.

From the tone of these letters, it was not obvious that Heinsius and Leeuwenhoek were old friends. In 1667, Heinsius, then in his mid-20's, became Delft's city attorney after Leeuwenhoek, ten years older, had already been working at the Stadhuis since 1660. They worked together for twelve years until Heinsius became became pensionary for Delft in the States of Holland, the same year that Leeuwenhoek was appointed the city's wine gauger. By the time they wrote these letters in the mid-1680's, they had become the two people from Delft most prominent in the larger world, Heinsius for his diplomatic skills and Leeuwenhoek for his research skills.

Specimen origin

Leeuwenhoek did not say where he got the cochineal. He wanted to compare them with the local insects, and he explained exactly how he acquired them.

Our little children usually go in the early part of the year (when the dead nettles flower) to look for some small flying creatures, which may generally be found on those nettles, and which they call ‘golden cockerel’ i.e. leaf beetles on account of their beautiful shiny bodies; as well as a species of these animals whose head is shiny, and the rest of the body reddish. These latter they call ‘compolie’.

And as I was speculating about these two species of little animals (although they are smaller than the animals whose bodies are cochineal) I instructed some children to catch these animals for me; as I thought that, when I had deprived the same of their shells, wings, head, and legs, they would then correspond to the shape of the cochineal.

After examining them, he concluded:

Although the abdomens of the cochineal, differ somewhat from those golden leaf beetle and the ‘compolie’, I could assure myself more than before that not only the little animals that produce the cochineal, but also the abovementioned little animals come forth from worms.


Plate from
Continuatio Epistolarum

Figures 1 - 5

The original drawings are lost. The Dutch and Latin editions that Leeuwenhoek published used the same plate with all five figures. The one below (click to enlarge) came from the 1730 fourth edition of Continuatio Epistolarum, as did the images on the sidebar. In the text, Leeuwenhoek noted that someone else drew the figures.

Other publications

While the Royal Society did not publish this letter in Philosophical Transactions, it was extracted twice in foreign journals, as were all the letters in Vervolg der Brieven, Letters 53 through 60. In the year after it was written, Jean Le Clerk published a short excerpt, including none of the figures, in Bibliothèque universelle et historique, vol. 9, p. 163-164.

In 1689, Otto Mencke pubished a short excerpt, including none of the figures, in Acta eruditorum, vol. 8, p. 174.