On the circulation of the blood in an eel and the passage from the arteries to the veins.
On the coagulation and crystals of sugar candy.
On the shape of some sulphur containing minerals from Hungary.
Description of a new apparatus, which he called a fish viewer (viskijker) to view the circulation of the blood in a living eel.
At the beginning of this letter, Leeuwenhoek rescounted what he showed to his visitors, no doubt using the fish viewer that he described at the end of the letter.
I have shown the said gentlemen, among other discoveries, the circulation of the blood in an eel, and in particular how the blood dropped into the veins as it were through a valve, which movement we call a pulsation. Although the evening was falling when they came to me and they therefore had to make shift with candle-light (which I avoid, in particular for seeing the flow of the blood), all three saw it so clearly that they told me that they could bear witness to this.
