"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.
By these observations I have proved better than before that there are no openings in our epidermis for the sweat to pass through.
From this it appears that our body is as it were only one pore, whereas our physicians are forever talking about the pores or orifices for perspiring of our body, as if special openings had been supplied for this purpose in our body.