Wrote Letter 42 of 1684-07-25 (AB 81) to Members of the Royal Society about parts of the brain of several animals, chalk stones of gout, leprosy, and the scales of eels

July 25, 1684
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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 nineteen quarto pages, written and signed by Leeuwenhoek, is preserved at the Royal Society (MS. 1901. L 1. 72). It is the first letter with scientific observations that he addressed to the members of the Royal Society in general rather than to one individual. After that, of the letters with scientific observations that he sent to the Royal Society, he sent to the member in general, though he used a variety of phrases to indicate them. Letters sent to individual members were more administrative and not intended for publication.


The original drawings are lost. The six images appeared on two plates. Below is the plate with Figures A through D. Figs. 1 and 2 are on the same plate to show the proportion. The scans came from Opera Omnia, the fourth edition of Arcana Naturae Microscopiorum.

Plate from
Opera Omnia

Figures A-D

In the text, Leeuwenhoek notes that he drew the simple figures.

I have drawn some of them in order to have a better idea of their length as compared with their thickness.

However, for Fig. 1:

I ordered a man, who does engravings to make a drawing of it as he saw it through a magnifying glass. But when he was occupied with this commission, he told me, that he could make an engraving of it as quickly as he could draw it, so I therefore ordered him to make an engraving of it, a copy of which is shown here.

Even engraving had its limits. Leeuwenhoek continued, referring to Fig. 1:

Part B, like all the other scales, pointed towards to tail. These scales are composed mostly of little round as well as oval balls, which little balls showed in many places little figures, which looked like a bit of a spider's web and, because of the extreme delicacy and smallness of their structure, could not be drawn.