ANTONIE van LEEUWENHOEK.

...[re]maining only a small opening in the pointed part G. Considering that, once the glass was heated, the air contained within the glass would reach the same temperature as the air outside; however, after a quarter of an hour had passed, I closed the opening G very tightly with the help of fire Leeuwenhoek is describing the process of flame-sealing a glass tube to ensure it is airtight.. I also prepared another glass for myself, which I treated in the same way, except that I did not close the opening G, so that I might observe, if possible, in which water living little animals animalcules original: "animalcula" — Leeuwenhoek’s name for the microscopic organisms he discovered, such as bacteria and protozoa. would first appear. But when it had remained thus for three days, and I had observed it frequently during that time, I concluded that even if the smallest living animalcules had been in the water, it would have been impossible for me to detect them, because the glass was too thick, and because many particles of pepper, which lay inside against the sides of the glass, did not allow for such accurate observations as were required. Therefore, I poured a little water out of the small opening G of the second glass, and in it I encountered a great number of living animalcules of various kinds, moving among themselves according to the speed of each kind.

But since the first tube was made of thinner glass, I left it closed until the fifth day, and in the meantime I observed it frequently, but I could detect no living animalcules. Then I decided to break the glass at point G; during this breaking, the air—which had been enclosed in the glass for five days (and which was greatly compressed by the air bubbles that were carried upward from the water here and there)—burst out of the glass with great force. For this reason, I imagined to some extent that there would be no living animalcules in this water; but I saw the opposite. For I had hardly exposed the water from the small opening G to my sight than I saw a certain kind of living animalcules that were round and larger than the largest kind of those I said were in the other water. Nevertheless, they were so tiny that I could in no way recognize them through the glass tube itself. However, after that tube had remained open for 24 hours, I observed the water again and saw, besides the aforementioned animalcules, various other kinds, but so minute that they could not easily be distinguished.