Wrote Letter L-135 of 1683年09月17日 to Francis Aston about saliva, nasal hairs and blackheads, skin, pores, calluses, and cleaning teeth; the discovery of bacteria in tartar

This letter was in the first batch that Gaesbeeck published. 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 these summaries.

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. This letter survives in bundles with Letters 32 and 33, in later edition bound between them, other times bound last, as in the volume here titled Onsigtbare geschapene waarheden (Dobell #1). It is also sometimes found bound after Letter 37 in the volume here titled Eyerstok (Dobell #3).

About six weeks after it was written, this letter was received at a weekly meeting of the Royal Society (Birch's History, vol. IV p. 219). First, the members listened:

These claims interested the members, some of whom doubted Leeuwenhoek.

Others seemed to affirm Leeuwenhoek's observations, which led to speculation and questions:

The year before Leeuwenhoek began publishing his own letters in Dutch, he wrote about the value he found in their publication in Philosophical Transactions.

From your welcome letter of 17 August O.S. I see the gratitude of the Royal Society for my latest observations. I was glad to hear this and especially to read what you say about their going to be printed in the Philosophical Transactions because then the world may know how far I have proceeded in discovering the great secret of generation.

He followed that with a comment about two unnamed noblemen.

I was also glad to hear that you offered to take the two noblemen whom I addressed to you, to a meeting of the R.S., merely for my sake. They ought to have accepted this great honor. In a letter from London they write about this, saying that they had no other reason (for not accepting it) than the fact that they did not know English and thus feared to incommode the Gentlemen.

He appended a personal request.

I am looking forward to the Transactions mentioned in your last letter; please send them to Rotterdam, bearing this direction: To Mrs. Catherina Leeuwenhoek, Hoogh-straat int Oude Gemenelants huis at Rotterdam.

"He had never washed his mouth all his life."

This letter is often cited as the first unambiguous observation of bacteria. If so, these creatures were the smallest that Leeuwenhoek saw which means his lenses and his technique never got better than they were in the mid-1680's.

I am in the habit of rubbing my teeth with salt in the morning, and then rinsing my mouth with water. After eating I usually pick my molars with a tooth-pick and also rub them with a cloth quite vigorously. This keeps my teeth and grinders so clean and white that only few people of my age can compare with me. Also when I rub my gums with hard salt, they will not bleed. Yet all this does not make my teeth so clean but that I can see, looking at them in a magnifying glass that something will stick or grow between some of the molars and teeth, a little white matter, about as thick as batter.

This is one of two (?) letters in which Leeuwenhoek may well have referred to his wife Cornelia and his daughter Maria, though not by name. He looked for little animals in their mouths, but of course, they cleaned their teeth often.

I also took spittle from the mouths of two different women, who, I am convinced, daily cleaned their mouths, and I examined it as closely as I could.

He let his own mouth go unclearned, but only for three days.

I did not clean my mouth on purpose for three days and then took the matter that, in a small quantity, had stuck to the gum above my front-teeth; this I mixed both with spittle and with clean water and discovered a few living animalcules in it.

What about children and people who did not clean their mouths as often, if at all?

I have also examined the spittle of a child about 8 years old.

While an old man (who leads a sober life and never drinks aqua vitae or tobacco and very seldom any wine) was talking to me, my eye fell on his teeth, which were all coated over; this made me ask him when he had last cleaned his mouth and the reply was, that he had never washed his mouth all his life. So I took spittle from his mouth and examined it, but could not find in it anything but what I had seen in my own spittle or that of the others.

I also took the spittle and the white matter, lodged upon and between his teeth from an old man who is in the habit of taking aqua vitae in the morning and of drinking wine and tobacco in the afternoon, wondering whether the little animals could live in spite of this continual drinking. I judged that this man, because his teeth were so uncommonly dirty, would not clean his mouth; when I asked him, he answered: never in all my life with water, but every day by flushing it with aqua vitae and wine. Yet I could not find anything in his spittle in addition to what I found in other saliva.

He concluded this part of the letter:

Especially in those who never clean their mouths, owing to which such a stench comes from the mouth of many that one can hardly bear talking to them. Many call this a stenching breath, but actually it is in most cases a stinking mouth. For my part, I judge from my own case, although I clean my mouth in the manner heretofore described, that there are not living in our United Netherlands so many people as I carry living animals in my mouth this very day.

He then returned to the study of what he called "nose worms", which he had first reported on in Letter 34 of November 4, 1681. He got specimens from his own face and from those of several other people living in Delft.

After being told that a large number of worms had been taken from a certain man's face I asked this person to come to my house and took both from his nose and his face quite a number of these so-called worms which I put upon a piece of clean glass for examination when I could be alone.

Looking through a magnifying glass I saw that in the lower and thicker part of my nose, close to my face, there were unusual little black spots which I at once pressed out. Examining these I was astonished to see that they consisted of quite a bundle of little hairs.

I also pressed these so-called worms from the lower part of the nose of a man and of a woman and found many hairs in them.

But when I pressed these supposed worms from a higher part of the nose there were very seldom hairs in them except in those taken from a certain man, who had very dark and thick hair.

Strength of his lenses

Leeuwenhoek made a comment about how he used lenses of different strengths.

For at first I saw through an ordinary microscope much more distinctly the particles which seemed to me to be round and to lay united; and in my opinion they were so small that a grain of sand would cover 200 or 250 of them, that is to say those parts of the scales which can be seen by our eyes or on which the light falls and which I have indicated by fig. H. But on examining them through a stronger microscope I saw that they were not made by the moisture exuded from our body.

If Leeuwenhoek's lenses let him see bacteria, it is surprising that they did not let him see the pores in skin, humans or other mammals'. In this case, the local physicians were correct.

In this letter, Leeuwenhoek did not directly respond to any other researchers. However, he ended the letter by responding to a request by the Royal Society.

"They vowed they would never use vinegar again."

Again, Leeuwenhoek commented on how others viewed him.

I have had several gentlewomen in my house, who were keen on seeing the little eels in vinegar; but some of them were so disgusted at the spectacle, that they vowed they would never use vinegar again. But what if one should tell such people in future that there are more animals living in the scum on the teeth in a man's mouth, than there are men in a whole kingdom? Especially in those who don't ever clean their teeth?

Figures

The original drawings are lost. The Dutch and Latin editions that Leeuwenhoek published used the same plates placed throughout the text. Two of those plates had more than one figure (see below; click to enlarge). They, as well as the scans on the left sidebar, came from the 1695 first edition of Arcana Naturae Detecta.

In the text, Leeuwenhoek does not say who drew these figures. However, they were well within Leeuwenhoek's skills, so he probably drew them.

Fig. 1 appeared between Fig. G and Fig. H. It may have been a late addition or re-arrangement after the other figures had been engraved. It could also be the letter I, not the number 1, which was the decision made by the editors of Alle de Brieven / Collected Letters. However, in all of the Dutch and Latin editions printed under Leeuwenhoek's supervision, the typesetters used the same cast piece for the 1 in the page numbers that they used for this figure when they referred to it in the text. On the same pages, they several times used a capital letter I, so it was readily available. If it is indeed the letter I, it would be out of alphabetical order, coming before H, not after it.

Fig. G was not included in the first edition printed by Gaesbeeck in 1684. The edition published by Kronevelt ten years later had the same plate with Fig. G added (right; click to enlarge). That plate was used in all subsequent editions.

In Philosophical Transactions, this letter was published in two parts, in 1684, volume 14 number 159 and nine years later (after the editorship of Edmond Halley) in 1693, volume 17 number 197.

On other journal published an extract during Leeuwenhoek's lifetime, Historia naturalis et medica latorum lumbricorum in 1715.

After Leeuwenhoek's death, Genees-kundig Verhaal published a quotation from the beginning of the letter in 1745.

Collection académique published most of the letter and nine of the ten figures in Vol. VII pp. 64-68 in 1766. Finally, a short extract and one figure were published in Abhandlungen zur Naturgeschichte, Physik und Oekonomie in 1780.