Wrote Letter 38 of 1683-07-16 (AB 72) to Christopher Wren

July 16, 1683
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Leeuwenhoek's summary

From the three editions of Onsigtbare verborgentheden and translated into Latin for all of the editions, some re-titled, of Anatomia Seu Interiora Rerum.

Ontledingen en Ontdekkingen. Van de voort-teelinge des Kik-vors, desselfs Mannelijk Saad, Bloed, Vleesch, Bloed-vaten, ende Dierkens in de excrementen van de selve. Van de voort-teelinge van Vogelen ende Visschen. Gestalte van de vleesch-musculen. Verbrijselinge van de spijs in de maag en darmen. Excrementen van Cabbbeljauw. Groote beweging van het hart, en minder ommeloop van het bloed, en dat het hert door een al te lange uytrekkinge niet en kan weder inkrimpen.

Dissections and discoveries. Of the procreation of frogs, the male seed, blood, flesh, and blood vessels of the same, and little animals in the excrement of the same. Of the procreation of birds and fish. The structure of the flesh muscles. The crushing of food in the stomach and guts. The excrement of cod. Great movement of the heart, and less circulation of the blood, and that the heart through an already too long drawing out cannot shrink again.

Text of the letter in the original Dutch and in English translation from Alle de Brieven / The Collected Letters at the DBNL - De Digitale Bibliotheek voor de Nederlandse Letteren.

The original manuscript on twenty-two quarto pages, written and signed by Leeuwenhoek, is preserved along at the Royal Society (MS. 1897. L 1. 68).


The original drawings are lost. The Dutch and Latin editions that Leeuwenhoek published used the same plates, one for each figure, placed near the text discussing it. The scans on the left sidebar came from the 1708 third edition of Arcana Naturae Microscopiorum.

In the text, Leeuwenhoek noted that  he drew Figs. 1 and 3. The other three were well within his technical capabilities. Referring to Fig. 1, he wrote:

However, I have figured them as best I could.

He noted that he made Fig. 3 to show something new.

Because the circular constrictions or wrinkles of each separate fiber were more numerous than I had hitherto seen in the fibres of the flesh of an ox, a fly, a gnat, a flea and a louse, I made a drawing of a small bit of one of the fibres composing a frog's muscle, as in fig. 3.

In the manuscript, he did not give the third figure a number. He treated it as a plate and called them Fig. A, Fig. B, and Fig. C. However, in print, they became Fig. 3 A, Fig. B, and Fig. C.

In the manuscript, the fourth and fifth figures were numbered Fig. 3 and Fig. 4. However, in print, they became Fig. 4 and Fig. 5.