"My body is uncommonly thickly covered with hairs."
In the first part of this letter, Leeuwenhoek wrote about hairs. Discussing the four figures of a hog's bristle, he gave a rare insight into his technique of specimen preparation. He had a razor sharp enough to make sections thin enough for light to shine through to his lens. But even it left marks that could confuse him.
And though as a rule the notches left in a sharp razor, even when whetted on a good oil-stone, leave a great number of scratches in cutting hairs across, I yet perceived only few scratches while cutting this hair. In my opinion this was the only reason why I thus could discern the fibers of which the hair consists inside more distinctly than ever before. We can also see from the hair figured here that those err who maintain that all hairs are round. Nay, one might well say: so many hairs, so many shapes.
This observation, which contradicted a common opinion, was only possible because Leeuwenhoek had such good tools.
After looking at these hog's bristles, he wanted to look at human hair. He often used his own body as the source of his specimens. In this letter, he gave some details:
Though I am quite healthy, my body itches badly, but mostly in spring. I am firmly convinced that this is caused only by the fact that my body is uncommonly thickly covered with hairs; these in my case, come off in spring (except those of the scalp and of the beard), but I believe that the hair that covers the bodies of all human beings annually falls off.
Having found two other spots of my body, where hair falls off but which my eyes cannot reach, I have shaved off the hair on my hand in three different places. A few days running I observed these cut-off hairs and noticed that, while one hair grows rapidly, another will not grow at all.
I then saw to my great satisfaction that some of these hairs were going to fall off unaided, and pulling them out painlessly with a fine little instrument, I saw that, while hairs that are pulled out when they are firmly attached usually have thick roots; those which were on the point of falling off only had a sharp, pointed little root.
He followed up on this experiment in Letter 35, written the following March. Then, he wrote:
For I have now frequently shaved for as long as four months the hair of my hand with a razor, and observed with astonishment to what length it grows in a fortnight, while it will constantly keep short.
"I squeezed ... worms from another man's nose."
After that, he discussed what he called nose worms. Were they really living creatures?
In order to expel these supposed worms some physicians, especially those in the town of Aix-la-Chapelle, order a man to be put with his back turned towards a fire of oak-wood and his body to be smeared with honey, owing to which, both the sweetness and the warmth, the supposed little animals will protrude their heads further from the skin; then their heads are cut off with a razor.
When a certain gentleman had been treated in this manner at Aix-la-Chapelle, and had told me about it, I resolved to make some further observations concerning this. So I squeezed these supposed worms not only from my own nose where there are no hairs, but also from another man's nose at various times and must own that some people looking at them through ordinary spectacles, would swear to it that they are little worms, for some seemed to have heads.
In this case, he did not deplore other people's ignorance. He understood why they would call them worms. However, close observation let him explain what others could not see.
This was merely caused by the fact that this part had protruded from the skin and so had become much drier and darker in color than the part enclosed in the skin; and of all the numerous so-called little animals that I observed, not two were alike. I have cut up most of them into several parts and next observed them, but cannot say that I have seen any part that at all resembled a little animal.
But I did find in a very small number of them, very thin, short little hairs with roots, some at least 25, others 100 times thinner than an ordinary hair. When I saw this I was strengthened in my opinion that the so-called worms were merely the spots in which a hair ought to have been formed and that the food, which has formed the said thin hairs, was scanty and of short duration.
"Animals moving very prettily"
He had more things to explore that could be squeezed out of bodies. He used two words for it, drek and gangen, here translated as "dung" and "stool". See the Notes section below.
"I have sometimes seen animals moving very prettily," Leeuwenhoek wrote after closely examining his own excrement. And not just his own. He also put before his lens the excrement from cows and horses, including his own mare, and from chickens and pigeons.
I weigh about 160 pounds and have been of very nearly the same weight for some 30 years and ordinarily have a fairly thick stool in the morning, but at one time I occasionally had a looseness every 2, 3 or 4 weeks, so that I went to stool some 2, 3 or 4 times a day. But this summer this happened to me very often and especially when I partook of hot smoked beef or ham, which food I like to eat; indeed I was once afflicted with it for three days, and whatever food I took I kept in my body not above 4 hours, and imagined (for various reasons) that I would recover by drinking uncommonly hot tea, which I did several times with good success.
Ever curious, he had to look more closely.
This induced me several times, when my dung was so thin, to examine it; and now and then I noted down what food I had eaten and what drink I had taken, and what I saw but it would take up too much time now to tell all my observations.
I will only say that I have repeatedly seen in my dung many irregular particles of various sizes, most of them tending to a round figure and of a yellow color. It was these that make the whole substance look yellow to our eye.
He could not resist sharing one other observation, what he recently had for dinner.
Sometimes I have also seen in [my excrement] some particles of food that had not been digested, among others, for example, after I had eaten asparagus I saw very clearly the little tubes (the soft parts of which had been digested).