Visited by Cornelis Bontekoe

January 1, 1682

On 16 July 1683 (Letter No. 72 [38] wrote about Bontekoe and his 1682 book Reden over de koortzen,

Among the physicians there was one who often visited me and who told me in the presence of other gentlemen that he took great pleasure in my assumptions; that after leaving me some time ago with another doctor who had been one of our party they had philosophized the whole evening about my arguments; that he was going to write about it but that I should have all the credit, since he did not wish to plume himself on borrowed thoughts.

However, I have not found it in the booklets he has published since that day, so that I presume the said gentleman has forgotten all about it. In a little book which recently appeared from his hand, he writes that there is no fermentation in the blood, and, when speaking+ about the circulation of the blood, he says that, though the heart and the pulse beat rapidly, the circulation of the blood is none the quicker. This had been my opinion long before I spoke about it to this physician, and when I was asked what might be the reason I replied as follows.

In a letter on 30 March 1685, Leeuwenhoek quoted a passage from Collectanea Medico Phisical, a book by Stephen Blankaart: "Most amazing of all, however, is that our learned Cornelis Bontekoe cites the ever curious Leeuwenhoek as asserting that human sperma is replete with small babies, and so likewise in other animals, each according to its kind." Leeuwenhoek responded:

It is true that Mr. Bontekoe has often visited me in company with others; but never have I told him or anyone else in the world that the human semen is full of small babies. What I did say was that it is full of living animalcules or tiny worms which have long tails, and I have occasionally shown a drawing of their structure. For, just as we have no reason to say that some worms, while they are still swimming in water, are flying creatures, though creatures with wings will eventually emerge from them; or that the pip or core of an apple is a tree, though a tree will grow from it; it would be equally wrong to assert that the little worms in the human sperm are small babies, even though a child is formed from such a small worm. I must say that I feel most aggrieved at the way my arguments are distorted or maliciously misrepresented, and worse still that, by being thus committed to print, they gain common currency.

In September 1696, Leeuwenhoek wrote, referring to Bontekoe,

I recalled how I said a considerable time ago to a certain distinguished physician who was about to go abroad (who, while drinking tea at my house, very highly extolled and recommended that beverage, but on the other hand very much condemned and advised against the use of all acids and of fish, and said that he for one would not take them, as being unwholesome, thinking that he would thus prolong his life with eighty years, although the issue has shown that he had made a miscalculation and that perhaps, had he taken a little more acid and fish and less wine, his life might have been of longer duration) that I could not imagine that the use of acid and fish could be so harmful.

As Leeuwenhoek pointed out, Bontekoe did not live another three years, dying in 1685 at age 38. Thus, he must have visited Leeuwenhoek in 1682, the year he left for Germany, never to return.