"That in the end we may arrive at the very truth."
Judged in light of modern standards for scientific papers, Leeuwenhoek's letters lack focus. They seem to jump from topic to topic. In this letter, he gave an example of how one specimen related to another.
I all along intended to examine the disease called leprosy by the common people of this country, but I was prevented from this partly by the long spell of cold weather, partly by my observations of the crystalline bodies in the eyes, especially those of birds, on which I spent a lot of time before I could discern the course of the fibers; and after that I turned my attention to the brains of turkeys, which in its turn was an occasion for me to observe the brains of other animals.
Specifically, he wrote about the lens in the eye of a cow. He then looked at the eyes of hares and rabbits and saw the same structures. He found those structures again in the crystalline bodies he took from the eyes of fishes and birds. This part took a long time.
In spite of all my observations I have not been able to ascertain the actual structure.
I believe these are the little animals or the movement that some say they see in boiled water and take for the animalcules which I maintain I can distinctly see. But let us forgive them: they know no better.
Alle de Brieven / Collected Letters translates eenige seggen te sien as "some pretend to see" but that makes the following sentence confusing. They know no better than to pretend? In the more literal translation above, "some say they see", Leeuwenhoek gave them the benefit of good faith and then "they know no better" makes more sense.
In this letter, Leeuwenhoek turned his attention to a problem he found when he separated a lens from the rest of an eye so that he could study it. A dry lens shattered. How did a lens stay moist?
Nay, I have seen people who, while listening attentively, yet shut their eye-lids (according to my calculation) at least 6000 times in an hour, while others standing near them closed theirs about 2000 times.
It has also frequently happened to me and to others at my house, when looking through a microscope that we saw several little globules coming before our eyes. I firmly believed that these were thrust out from the vessels and filaments composing the tunic of the eye.
He did not name those visitors. His reference gives the impression that he often had them. Perhaps one of them ask the question he answered next in this letter: How does the skin of black people differed from those of white people?
I took from several parts of the arms of a black Moorish girl, about 13 years old, the outer skin with a fine little instrument.
Then he ran into a problem: not all the skin was dark.
The greatest difficulty I met in the case of the epidermis of Moors was the fact that the super-imposed scales (otherwise called callus) on the inside of the hands and feet, were always whitish.
He got more information about the girl. She had come to Delft perhaps as a servant to a family that had been lived in Brazil, where the Dutch established trading posts as early as 1630, two years before Leeuwenhoek was born.
But a certain old lady of this town to whom the grandmother of this Moorish girl had been a slave in Brazil, told me that this Moorish woman was the child of parents from Angola, and that although all Moors come red into this world and shortly after become darker, yet the inside of their hands and the soles of their feet do not become black, but take the white color which they have as they grow old. From this I concluded that the scales on the inside of their hands and on the soles of their feet are more transparent.
Then Leeuwenhoek directly countered a common belief of the time, one he "often experienced".
I know quite well that there are many people in our country (as I have often experienced) who are firmly convinced that the Moors become black merely by rubbing their bodies with a certain oil, for they say the children are red when they come into the world, just like our children. But just as it is impossible to dye the world, or the hair on the body of a sheep, a horse, or any other animal so that it retains this color, because the hair is shed, so also it is impossible to dye the scales forming the epidermis, so as to keep it black, because the scales are constantly shed, as I have said several times.
Always the good empiricist, knowing that his conclusions were only as good as his evidence, he concluded this letter:
As for my suppositions and conclusions, I readily own that they are very uncertain and need not be accepted. I would rather recommend you to reject them altogether and propose other theses instead of them, that in the end we may arrive at the very truth.
