This letter consisted of observations occasioned by the writing of three other researchers and a conversation with a physician. The first was unnamed by Leeuwenhoek but was noted by Alle de Brieven / Collected Letters as a reference to Regnier de Graaf's Een nieuw ontwerp van de ledematen der vrouwen, tot de voort-teelinge dienstig, which he had in the year before his death published in Latin under the title De mulierum organis generationi inservientibus (title page on right).
Having read a certain book, edited by a physician of this country and dealing with human procreation, in which the author writes at great length about the ovary of woman (as it is now called), I once more took the ovaries of a number of lambs, now about a year old, and fattened a few months in a stable this winter. These lambs rut every month, but no rams serve them. And I imagine that if anything could be said about the so-called ovaries of woman, those of quadrupeds could serve just as well.
In addition to responding to his old friend De Graaf, he was also involved with Cornelis 's Gravesande and the other physicians in the group portrait that Cornelis de Man painted the previous year. By demonstrating it in their presence, he could have been referring to one of the Wednesday afternoon meetings in the Theatrum Anatomicum.
This so-called ovary I have not only studied by myself, but have also demonstrated it in the presence of a certain learned Anatomist and other learned gentlemen and have there adduced the reasons why I cannot imagine why so many learned men agree with, and adhere to, the opinion that the tuba fallopiana sucks off or pulls off an egg from the ovary and transmits it through such a narrow channel as I showed the tuba fallopiana to have, the more so because the supposed eggs, that is to say the largest in the ovary, were as big as peas, nay, some as large as an entire ovary, mostly consisting of glandular parts, full of blood-vessels and so tightly enclosed in membranes that I was not able to tear off with my nails one of these so-called eggs.
Second, he responded to a false charge made about him in a book that the editors of Alle de Brieven / Collected Letters have not been able to identify.
In a certain book it is laid to my charge that I had proclaimed that a human being will originate from a little animal in the male seed, although I have on the contrary never expressed an opinion on this subject.
But now that I have discovered that the animalcules also occur in the male seed of quadrupeds, birds and fishes, nay even in vermin, I now assume with greater certainty than before that a human being originates not from an egg but from a little animal that is found in male seed, the more so since I remember having seen that in the sperm of a man and also of a dog there are two sorts of animalcules. Seeing these I imagined that one sort were males and the other sort females.
Third, he had a conversation with a local physician, unnamed, but they were discussing a remedy prescribed in several books at the time.
A certain physician told me that many people suffering from fever were entirely cured after having taken Sal volatile oleosum, because Sal volatile oleosum makes the blood very quick and thin. So I resolved to mix the Sal volatile oleosum with blood, in order to discover, if possible, its action on blood.
Fourth, he responded to a book that Alle de Brieven / Collected Letters identifies as Nieuwe beginselen tot de genees- en heelkonst, published in 1681 by Heydentryck Overkamp (title page on right).
A few days ago a certain booklet, recently published, fell into my hands, in which a physician of this country proclaims that there is fermentation in our blood, just as batter is made to rise by yeast, salt, and eggs; also that the fermentation is caused by the air which acts upon our blood, especially in the lungs and is mixed with it.
But to me it is inconceivable that air-bubbles are made in the blood. ... If there had been air-bubbles in the blood, though a thousand million times smaller than a grain of sand, I should certainly have discovered them in the numerous observations of the blood and the globules contained in it which I have made in the course of 11 or 12 years.
