Letters written by Leeuwenhoek during Period 6

Alle de Brieven / Collected Letters has over 350 letters. However, only those in this chronology that Leeuwenhoek designated Letter 1, Letter 2, etc. did he consider to contain publishable microscopic observations.

November 8, 1712 Wrote Letter L-488 of 1712-11-08 to Anthonie Heinsius, a cover letter for Letter L-489
November 8, 1712 Wrote Letter L-489 of 1712-11-08 to Anthonie Heinsius about the muscle fibres of a whale
December 17, 1712 Wrote Letter L-490 of 1712-12-17 to Anthonie Heinsius about salts in the blood of a shrimp and the muscle fibres and enveloping membranes of cod, shrimp, flounder, and perch
February 28, 1713 Wrote Letter L-492 of 1713-02-28 to Jan Meerman about wheat and barley grains, beans, peas, and chestnuts, vessels and membranes in coconut rind, and the embryo in an apple pip and in a coconut
March 14, 1713 Wrote Letter L-493 of 1713-03-14 to Jan Meerman about the eye of a whale, the lens, and the cornea and calculations of the pressure on a whale's eye at great depth
March 25, 1713 Wrote Letter L-494 of 1713-03-25 to Adriaen van Assendelft about little hairs of a mouse, mole, cat, and rabbit all have the same shape; thick, dark bear hair, composition and color of hair, hair of deer and elk
March 29, 1713 Wrote Letter L-495 of 1713-03-29 to Anthonie Heinsius about the muscles of cows, muscle fibers of mice thinner than whales, fat particles, muscle fibers of sheep same size as of mice and oxen, though the animals differ greatly in size
June 28, 1713 Wrote Letter L-496 of 1713-06-28 to the members of the Royal Society about little animals on duckweed, muscle fiber membranes, and a list of unanswered letters; little animals in his mouth come from rinsing glasses with pond water
June 30, 1713 Wrote Letter L-497 of 1713-06-30 to Anthonie Heinsius about the composition of crabs’ eyes and lobster and crab shells, ring-shaped structures in lobster pincer shell, compared to annual rings of woody vegetation, and the lobster's muscle fiber membrane
October 12, 1713 Wrote Letter L-499 of 1713-10-12 to Hans Sloane as a cover letter for a copy of Letter L-489 on muscle fibres of a whale and a request for new numbers of Philosophical Transactions and a list of fellows of the Society to be sent to relatives in Rotterdam
October 24, 1713 Wrote Letter L-501 of 1713-10-24 to Antony Cinck refuting, as requested, Kircher's ideas about poisonous little animals on sage leaves and spontaneous generation
June 22, 1714 Wrote Letter L-504 of 1714-06-22 to the members of the Royal Society to acknowledge Letter L-503 and numbers of Philosophical Transactions and to query why figures of the muscle fibres of whales were not published
August 21, 1714 Wrote Letter L-507 of 1714-08-21 to the members of the Royal Society about the muscle fibres of cow, chicken, mouse, honeybee, flea, ant, and whale and the blood vessels in the leg of a fly; thanks for recent numbers of Philosophical Transactions
October 26, 1714 Wrote Letter L-509 of 1714-10-26 to the members of the Royal Society about muscle fibres and enclosing membranes in the legs of a mosquito, rose chafer, fly, crane fly, honeybee and cow; rectifying earlier opinion, the contractions in a muscle are spiral
November 4, 1714 Wrote Letter L-510 of 1714-11-04 to Adriaen van Assendelft, comparison between muscle fibres and a tightened rope; the shorter the rope, the quicker it can shrink; application of this comparison on the size of muscle fibres of a cow and of a mouse
November 9, 1714 Wrote Letter L-512 of 1714-11-09 to the members of the Royal Society about the muscles of an ox, sheep, chicken, mouse, and hare
November 20, 1714 Wrote Letter L-513 of 1714-11-20 to the members of the Royal Society about muscle fibres and tendons from a mouse leg, a duck wing, a honeybee, a polecat leg, and between the ribs of a mouse; a theory about the structure and action of tendons
January 11, 1715 Wrote Letter L-514 of 1715-01-11 to Anthonie Heinsius, a cover letter for a copy of a recent letter on muscle fibres
March 26, 1715 Wrote Letter L-516 of 1715-03-26 to Antony Cinck about the structure and action of muscle fibres and tendons from the leg of a mouse and the head of cod and a wire model of spiral contraction
July 7, 1715 Wrote Letter L-518 of 1715-07-07 to Antony Cinck about contracting and stretching of muscle fibres and tendons; their connection in lobster and crab; no observed nerves between muscle fibres and membranes; cannot confirm that nerves are hollow
September 28, 1715 Wrote Letter L-521 of 1715-09-28 to Gottfried Leibniz about scholars who do not agree with Leeuwenhoek; sperm the same size in different animals; the pulse; posthumous letters; muscle fibers, tendons, and nerves; Hartsoeker; why he won't train students
November 18, 1715 Wrote Letter L-523 of 1715-11-18 to Gottfried Leibniz, a cover letter for Letter L-524
November 18, 1715 Wrote Letter L-524 of 1715-11-18 to Gottfried Leibniz about vessels in the flesh of fruit and in the seeds of various strains of pears, a pear's embryo and the structure of a pear's skin, and spiral vessels in tea-leaves
January 1, 1716 Wrote Letter L-525 of some years before 1716 to Frederik Adriaan van Reede about the large number of eggs in the roe of a ling
February 25, 1716 Wrote Letter L-526 of 1716-02-25 to Anthonie Heinsius as a cover letter to "notes" about tendons, muscle fibres, and starch grains
March 3, 1716 Wrote Letter L-527 of 1716-03-13 to Gottfried Leibniz about human twins, trees, birds, size of sperm, number of eggs in fishes' hard roe, structure of tendons and muscle fibres, the heart; does not want to be paid for research or to teach students
May 10, 1716 Wrote Letter L-530 of 1716-05-10 to Hubert Kornelis Poot to thank him for two published panegyrics; the size and origin of little animals; wonder at the smallness of little animals and the largeness of the universe; periwinkle seeds
May 16, 1716 Wrote Letter L-531 of 1716-05-16 to Gerard van Loon about hops from Liege, the structure of hops, its bitter oil, and salt particles from the oil, a comparison with sugar candy, and hop embryos; Leeuwenhoek descended from a family of beer brewers
May 19, 1716 Wrote Letter L-532 of 1716-05-19 to Gottfried Leibniz about muscle and tendon fibers, mammal teats, sperm; did not find eggs in ovaries, Fallopian tube, or womb; cannot imagine how the Fallopian tube could suck sperm; does not know the ovary's function
May 22, 1716 Wrote Letter L-533 of 1716-05-22 to Cornelis Spiering about the scales of a carp that Spiering sent him, using scales to age a fish, eggs in hard roe and sperm in soft roe food for other fishes, shrimp eggs, and the life span of whales and fish
June 12, 1716 Wrote Letter L-536 of 1716-06-12 to thank professors Cink, Narez, and Rega for the honorary medal; barley germination and nutrients; again rejects spontaneous generation
June 22, 1716 Wrote Letter L-537 of 1716-06-22 to Jan Gerard Kerkherdere about how wheat, barley, beans, peas, rice, buckwheat, and maize become food for animals and discusses Leeuwenhoek's techniques for preparing samples
September 17, 1716 Wrote Letter L-538 of 1716-09-17 to Abraham Cornelis van Bleyswyck about his own intestinal ailment and the roles of chyle, gall (bile), and the diaphragm in the digestive process
September 28, 1716 Wrote Letter L-540 of 1716-09-28 to Herman Boerhaave about how trees grow and withstand wind; coconut palm wood and nut; he acknowledges previous errors in his observations of coconut tree trunks
November 5, 1716 Wrote Letter L-544 of 1716-11-05 to Herman Boerhaave about the size of sperm from rams, cod, and ling, little animals from rain water and soil, and blood in arteries and veins
November 17, 1716 Wrote Letter L-545 of 1716-11-17 to Gottfried Leibniz about reproduction, numbers of sperm and seeds, reproductive organs of sheep and ram, fallopian tube too small to let eggs through
November 21, 1716 Wrote Letter L-546 of 1716-11-21 to Herman Boerhaave about ram sperm and details of his experimental methods
March 2, 1717 Wrote Letter L-547 of 1717-03-02 to Abraham van Bleyswyck about the structure of nerves and the associated fat in the spinal cords of cows and sheep
March 6, 1717 Wrote Letter L-548 of 1717-03-06 to the members of the Royal Society tendons and muscle fibres in sheep, flea, ox, honeybee, oyster, and mussel
March 6, 1717 Wrote Letter L-549 of 1717-03-06 to the members of the Royal Society about pig brains, apples, and coconuts; blood circulation nourishes; new technique to examine brains; tea and coffee keep the blood thin
May 6, 1717 Wrote Letter L-550 of 1717-05-06 to Ewout van Bleiswijk about dragonflies' muscle fibres, compound eyes, and corneal facets, flies, lobster, and crab
May 26, 1717 Wrote Letter L-551 of 1717-05-26 to Abraham van Bleyswyck about the structure of nerves and associated blood vessels and membranes, the structure of the spinal cord and brains of a pig, cow, and mouse, and the nerves of a calf, bream, and lamb
June 15, 1717 Wrote Letter L-552 of 1717-06-15 to the members of the Royal Society about the muscle fibres of an ox and a flea and the reproduction of fleas
July 6, 1717 Wrote Letter L-553 of 1717-07-06 to Antony Cink about how two doctors treated his recent illnesses with saltpeter and opium; saltpeter’s effects on the blood and its efficacy as a drug
July 13, 1717 Wrote Letter L-554 of 1717-07-13 to Jan Gerard Kerkherdere about one of his personal ailments, the consequences for the digestion of eating fatty meat, the particles in his own excrement, and the role of chyle and gall during digestion
August 18, 1717 Wrote Letter L-556 of 1717-08-19 to Adriaan Swalmius about membranes inside an eggshell, salt crystals from an eggshell, and how birds and oysters produce shells
August 26, 1717 Wrote Letter L-557 of 1717-08-26 to Herman Boerhaave, following up on Letter L-546, about a ram's seed balls, vas deferens, and epididymis, millet grains or mustard seeds as units of measurement, sperm compared smaller little animals, and a sperm’s tail
September 10, 1717 Wrote Letter L-558 of 1717-09-10 to Frederik Adriaan van Reede about haddock intestines, roach and cod, and how scales determine the age of herring, perch, bream, and cod
September 17, 1717 Wrote Letter L-559 of 1717-09-17 to the members of the Royal Society about his own skin's fat globules and sweat ducts, holes in his finger nails, sweat ducts in humans and in cow teats, and how lice and fleas use sweat ducts to obtain their food
October 8, 1717 Wrote Letter L-560 of 1717-10-08 to the members of the Royal Society about Pareira Brava root and the effect of salt particles from it upon blood, starch grains from the membranes of the root, and the roots of “China” and “Irias"
October 22, 1717 Wrote Letter L-561 of 1717-10-22 to the members of the Royal Society about the brain of a cod, the nerves of cod and haddock, and the spinal cord of haddock
November 20, 1717 Wrote Letter L-562 of 1717-11-20 to the members of the Royal Society about tendons and nerves of sheep, lamb, cow, and ox; his last letter to the Royal Society; expresses his gratitude for being elected a fellow and for Philosophical Transactions
November 28, 1718 Wrote Letter L-564 of 1718-11-28 to Francesco Corner, a cover letter for Epistolae Physiologicae