Wrote Letter L-111 of 1680-11-12 to Robert Hooke about blood globules, lees of wine, globules in rain water, milk vessels, reproduction, little animals in the male seed of animals, and their incomprehensible smallness

Date:

November 12, 1680

Standard reference information

L-number:

L-111

Leeuwenhoek's number:

Collected Letters number:

Collected Letters volume:

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 on seventeen quarto pages, written and signed by Leeuwenhoek, is preserved along with both figures at the Royal Society (MS. 1881. L 1. 62). It had eight small drawings in red chalk and ink pasted onto two folio pages. An English translation is found at Early Letters L1.63.

Robert Hooke published an excerpt from this letter in Philosophical Collections, no. 3, dated 10 December 1681. See Publications history below.

Leeuwenhoek's summary

This letter did not have a summary. It was the second or third letter in the first publication by Gaesbeeck, Onsigtbare geschapene waarheden.

Four years later in 1688, when Leeuwenhoek published Vervolg der Brieven, he preceded the letters with summaries of all of the previously published letters, including this one, in a section titled Register der Saaken in the voorgaende Brieven vervat (Register of topics contained in the foregoing letters). Later editions and the Latin translations included this summary.

From the summary below, it seems that Leeuwenhoek saw them as one volume under a common title: Ondervindingen en Beschouwingen. In 1684, he numbered each letter separately, but in 1694, he numbered them continuously.

33e. Missive, van dato den 12. November 1680. gedrukt by Daniel van Gaasbeek, in een Boekje genaamt Ondervindingen en Beschouwingen. Waar in gehandelt werd: Van de makinge van de bloed-Globulen, Moer van Wijn, Stomme wijn, Globule in Reqen-water, Melk-vaten, van Melk, vaten in kleyne Dieren, voorteelinge; dierkens in de mannelijke Zaden van Dieren, onbegrypelijke kieynheyd van Dierkens in 't water.

33rd Letter, of Nobember 12, 1680 printed by Daniel van Gaarbeek, in a little book named Experiences and Contemplations. Wherein was treated: of the making of blood globules, lees of wine, mute wine, globule in rain water, milk vessels, of milk, vessels in small animals, reproduction; little animals in the male seed of animals, incomprehensible smallness of little animals in water.

Reception in London

In this letter, Leeuwenhoek made no mention of his concern about a lack of reponse to his letters addressed to Hooke and Gale. However, in the previous two letters, he said that he would not send new observations until he received a response. It is reasonable to assume then, that he did so before he sent this letter in mid-November. It would be a year, until November 1681, before he sent another letter with scientific observations.

By the end of November 1680, this letter was read at a meeting of the Royal Society (Birch's History, vol. IV, p. 56, 57):

Mr. Hooke produced a long letter lately received by him from Mr. Leeuwenhoeck. It was written in Low Dutch; but the contents of the several heads were read by Mr. Hooke. It was desired, that the said letter should be translated and answered.

Two weeks later:

Mr. Aston took Mr. Leeuwenhoeck's last letter, and promised to translate it into English.

At the meeting on January 12/22, 1681:

Mr. Aston having translated a long letter of Mr. Leeuwenhoeck from Low Dutch into English, part of it was read, containing divers observations on the Iees of ale and wine; and the remainder was referred to the next meeting.

There is no mention in Birch's History that the remainder of the letter was ever read.

Specimens and methods

"I then made several sorts of glasses"

In the text, Leeuwenhoek noted that he made the glass tool in Fig. 1:

I then made several sorts of glasses but all for the same purpose and among them a glass like fig. 1, ABCD, which has an opening only at A.

The public and their opinions

"I only tell fictitious stories about the little animals."

Leeuwenhoek addressed how he was perceived by others, which concerned him even though as a commited empiricist, he had to insist: if I see it, it exists. For example, in this letter he wanted to see how:

the blood in its circulation is poured from the smallest branches of the arteries into the smallest branches of the venae, and that therefore the arteries and the venae are so to say connected.

Discussing Fig. 2, vessels in the breathing tube of a fly he came up with some very large numbers:

however accurately I tried to observe them, I could not see the junction and when the extreme ramifications appeared to me more than two hundred thousand times smaller than a hair from my beard I yet saw no junction.

He was still several years away from seeing the passage of red blood cells through the capillaries between arteries and veins, but meanwhile, he had expressed his problem: Two hundred thousand times smaller than a hair that people could barely see in the first place?

And as this computation of proportions may appear strange to many, I will show how I made my calculation. I have a scaled brass ruler and accurately observe through a good microscope how many divisions one of the thickest hairs from my beard will cover on the scaled ruler; for instance, the diameter of such a hair seen through a microscope has the length of 50 divisions. I then draw on the brass ruler, with the point of a needle, a line such as will appear to my naked eye like the thinnest vein of the fly seen through my microscope

Then he did the math, and the two hundred thousand grew by an order of magnitude!

I think that if 9 of such lines as I drew with the point of a needle lay side by side they would equal 1/50 of the diameter of a hair. If therefore 450 diameters of the thinnest veins, distinctly seen by me in a fly, equal the diameter of a hair from my beard, then a hair from my beard is two million times thicker than the thinnest blood-vessels of a fly.

"Two million times" was very difficult for people to accept. At the end of this letter, he addressed that problem directly:

As it has often reached my ear that I only tell fictitious stories about the little animals, and whereas I suffer many contradictions, and as there are gentlemen in France who venture to say that those are not living little animals which I show, and that if such water be boiled the particles which are supposed to be animals still continue to move, yet I have demonstrated the contrary to several distinguished Gentlemen. And I do not hesitate to say that the above-mentioned gentlemen have not advanced so far that they are able to make good observations.

He tried personal testimony:

As for me, I can say with perfect truth that I can put the smallest sort of which I shall here speak as distinct before my eyes and can see that they live, as if we saw with our naked eyes little flies or gnats flitting about in the air, although they are more than a hundred million times smaller than a coarse grain of sand; for not only do I observe their progress both when they hurry and when they slacken speed, but I see them turn about, stand still and in the end sometimes die; and those that are bigger I can distinctly see running along, as plainly as we see mice before our naked eyes; nay, in some I can even see the interior parts of their mouths being protruded or retracted, as if they played with them.

Calculations

How small are the little animals?

Finally, he again showed his math, explaining how he used the diagram in Fig. 8:

And as it seems so incredible that this great number of little animals can be enclosed in a sand-grain, as I have maintained, and as they say that I cannot make a calculation, I have in order to put the matter yet more clearly, devised this proportion. Let me suppose, for instance, that I see a sand-grain only as big as the sphere ABGC in fig. 8.

He walked the reader through his logic with these proportional circles.

More than 110 million animalcules being as big as a grain of sand.

To sum up: a thousand million living animalcules are as big as a coarse sand-grain.

He made no further comment, willing to let the arithmetic speak for itself.

Figures

The original drawings are preserved by the Royal Society. Two of these figures were drawn in ink, Fig. 6 the common fly and Fig. 8 the sphere to show proportion. The rest were drawn in red chalk. The Dutch and Latin editions that Leeuwenhoek published used the same plates.

In their first appearance, Onsigtbare geschapene waarheden, was published by Gaesbeeck in 1684. All eight figures were placed in the text where Leeuwenhoek discussed them, even Figs. 1 and 8, which could easily have filled a page themselves. However, for the 1695 first edition of Arcana Naturae Detecta, published by Kroonevelt, Figs. 4 and 5 were combined on one plate inserted on a separate unnumbered page between pages 18 and 19.

In the text, Leeuwenhoek noted that he drew the first two, Figs. 1 and 2.

I also slanted the glass tube at least as much as I have figured here.

I have drawn these vessels the size I observed them in my microscope.

The next two figures required drawing skills beyond Leeuwenhoek's.

Not knowing whether these insects are known in your country I ordered a drawing to be made of them, and on the other hand also because the copulation of these animals seemed strange to me, for while one during the copulation moved onward on its legs the other was dragged along on its back. In fig. 3 ABCD is the male during copulation, D being the genitals, which ought to have been drawn in somewhat closer union. EDFG is the outline of the female.

And because I do not know whether these animals are found in your country I have had a drawing made of them, fig. 4 ABC being the female and CDE the male, sticking together while they flew.

He drew the next one, Fig. 5:

I have also drawn one of them in fig. 5 AB, which, being dead, had kept the curves which it had used in its progress.

If Figs. 3 and 4 were beyond his skills, so was Fig. 6, though he did not say explicitly that he had it drawn. He did not say anything about Figs. 7 and 8 either, though neither was beyond his skills.

Publication history

Related sources, especially Philosophical Transactions, and first editions only of Leeuwenhoek's volumes of letters. For later editions see Related events under Learn more.

Year	Author	Title
1679 - 1682	Hooke, R.	Philosophical Collections
1681	Leeuwenhoek, A. van	Some Microscopical Observations made by Mr. Anthony Leuwenhoek, concerning the Globulous Particles in Liquors, and the Animals in Semine Masculino Insectorum
1682 - 1731	Mencke, O. (ed.)	Acta eruditorum
1684	Leeuwenhoek, A. van	Onsigtbare geschapene waarheden
1695	Leeuwenhoek, A. van	Arcana Naturae Detecta
1754 - 1787	Berryat, J. (ed.)	Collection académique
1948	Leeuwenhoek, A. van	Alle de Brieven. The Collected Letters. Volume 3

Other publications:

This letter was the second of Leeuwenhoek's letters published in Philosophical Collections in 1681. The following year, Otto Mencke published an extract in Latin translation, along with 7 of the eight figures, in the first volume of Acta Eruditorum (pp. 321-327). He probably translated it from Philosophical Collections.

Three decades after Leeuwenhoek's death, Jean Berryat published excerpts in French translation in volume II of his Collection Académique (pp. 540-545) but did not include any of the figures.

Notes

In this letter, Alle de Brieven / Collected Letters uses both "my private room" and "my closet" to translate comptoire. Leeuwenhoek often refers to this room, which is more accurately thought of as a small office or workroom on the floor above the ground floor of his house. Its window looked out on the Hippolytusbuurt gracht.

Learn more

Period 2 - 1679-1686

Structure of the letters in Period 2

1680: Member of the Royal Society

Specimens: Sperm

Specimens: Currant bush and seeds

Counting the Little Animals

Spontaneous generation

1681-82: Hooke's Philosophical Collections

Related people:

Robert Hooke

Hendrik d’ Acquet

Related events:

Date	Event
November 21, 1680	Robert Hooke read the headings of Letter L-111 of 1680-11-12
December 5, 1680	Francis Aston promised the Royal Society to translate Letter L-111 of 1680-11-12 into English
January 22, 1681	The Royal Society read Francis Aston's translation of Letter L-111 of 1680-11-12 about the lees of ale and wine
December 10, 1681	Philosophical Collections number 3 published in London, including Leeuwenhoek's Letter L-111 of 1680-11-12 to Robert Hooke
January 1, 1684	Daniel Gaesbeeck wrote Letter L-145 of 1684-01-01 to Leeuwenhoek about why he was publishing his letters
January 1, 1694	Published Onsigbare Geschapene Waarheden (Invisible Creation Truths), Letters 32, 39, 33

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Wrote Letter L-111 of 1680-11-12 to Robert Hooke about blood globules, lees of wine, globules in rain water, milk vessels, reproduction, little animals in the male seed of animals, and their incomprehensible smallness

"I then made several sorts of glasses"

"I only tell fictitious stories about the little animals."

How small are the little animals?

Figures

Life in Holland

in the 1600's