Wrote Letter 57 of 1687-08-06 (AB 102) to Members of the Royal Society

August 6, 1687
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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 manuscript is lost. The transcript in Alle de Brieven / Collected Letters is from Vervolg der Brieven.

There is no record in Birch's History that this letter was received or read at a weekly meeting.

Public reception: "Those who cannot see past the end of their nose."

Leeuwenhoek began this letter by telling why he studied calanders. His contemporaries did not understand where little creatures like insects came from, for example, the pests that infested grain storehouses.

Some persons have been doing their utmost to make me believe that the calander and the wolf (... both well-known everywhere in this country among corn merchants and bakers) are generated without reproduction.

The principal reasons that those people adduced were these:

The wheat, having been carried to a new loft, where no wheat has ever lain before, gets the calander growing inside it, and this must happen without any propagation.

On the other hand, they say:

We may open up a lot of wheat that is quite sound and uninjured, without there being the slightest tiny hole on the outside; and there will be an adult, living calander sitting inside it.

Where could the little beetle have come from? Certainly not from the wheat itself. Therefore, common sense said, it must have been generated out of nothing. Leeuwenhoek had his own "common sense".

I have tried to convince them by reasoning, and I said, among other things, that we might easily, without knowing it, carry this vermin from one loft to another.

He gave two plausible scenarios.

For, only let a worker that stirs the corn, leave a corn-loft where there is calander, and the same may very easily carry a few wheat-grains with the calander inside, or the calander itself, along with him, either on his clothes or his boots, without knowing it, to a loft where no calander had been before.

And on the other hand, the ship, waggon or cart, in which the corn was transported, may be infested with calanders, because of having previously carried grain in which there had been calanders; and from those few transmitted calanders, the calander may be generated by propagation.

At the end of the letter, he returned to this situation and the public reception of the implications of his observations:

I might add several more of my notes, which I kept while shutting up and observing the calanders, to this letter; but I believe that what I have related here is sufficient to prove to Your Honours, and to all learned intellects, that the calanders cannot originate in any other way than through propagation; namely, that a calander mates, lays eggs, and that worms come forth from those eggs, and that those worms turn into calanders.

But whether this will be sufficient for the corn dealers, bakers, millers, and those who cannot see past the end of their nose, and from whom I have had to put up with so much contradiction concerning reproduction, I am still inclined to doubt.

Souls and miracles

Based on the breadth of his observations and his principle of a great degree of uniformity in nature, Leeuwenhoek generalized from these beetles to all living creatures:

I definitely assert that, just as I have now clearly proved with regard to the calanders; that they cannot originate except through propagation, so it must also be with all creatures that are endowed with movement; (that which we call, in animals, a living soul) for however small it may be, its first production depends upon the beginning of Creation.

If this were otherwise; namely, if from immobile substances such as stone, wood, earth, plants, seeds, etc. a body came forth that (as said above) was mobile, that would be a miracle and its production would once again be dependent upon the great almighty Creator.

It is unclear whether the calander beetle's soul had the same nature and status as the human being's soul. Still, Leeuwenhoek had the problem of where this soul came from. Did each one of the "unimaginable large number" of little animals in male seed have a soul? He called them living (levende), so apparently they did. Not only that, all of these souls had existed since the beginning of creation.

And just as I said in one of my foregoing missives, that no tree is newly-made, but that they all depend upon the beginnings, or young plants that are in the seeds; so all creatures that are endowed with a moving or living soul, depend upon their first generation; or to put it in a better way, they depend upon the moving or living animals that were made in the male seeds, in the beginning of Creation.

This will probably seem strange to some people, and they might perhaps refer me to the propagation of other small animals; but whoever wants so much work as I have spent on this examination of the calander (which has occupied me, on and off, for more than four months).

Leeuwenhoek was struggling to reconcile what he saw before his eyes and the assumptions of his time about the nature of living things that stretched back at least to Aristotle.

Specimens and methods: beetles in his pocket

At several places in the text, Leeuwenhoek mentioned that he carried the calendar beetles around in his pocket.

And as the weather was cold, and these animals were mostly lying without any movement, I carried the small glasses in leather cases in my pocket. I had no other though but that I should be able to demonstrate clearly to the World that the calander comes forth from a worm.

Also, he showed visitors what he was currently examining, even to the point where he negatively affected his ability to observe.

My intention was to cut open the calanders that had, therefore, been shut up in the glasses for a long time; but since at that time several prominent gentlemen of our country came to visit me, it was not long before all the calanders had run away.

He found sperm in male calanders and used a vivid metaphor to describe them.

After this I began to search for the male seed of the calander; and I collected about as much as a coarse grain of sand of that substance, and I brought it before my vision through a very good and greatly magnifying microscope, and discovered an unimaginable large number of living creatures in the said minute quantity of substance, so that it is, for him who does not see it himself, unbelievable.

Nay, I imagined that no commander in the field, though he might see two field armies in action against one another, which together numbered fifty thousand, could see such a multitudinous movement of people, as I saw animals moving in the aforesaid minute quantity of the male seed.

Sometimes upon further examination, Leeuwenhoek revised his first impressions:

This supposed male organ I have taken out of the calander, and placed it before a microscope, as shown here in Fig. 3. MLKN.

But as I inspected it more closely with greater attention, I found that I had been deceived in my opinion; for this part was no male organ, but only a case, or sheath, of the male organ; and whereas this sheath was hard, or horny, the male organ, on the contrary, was soft and pliable, and from the same there evaporated (when it was in the air) much moisture, which made it thinner.

Royal visitor

Leeuwenhoek was not one to drop names. He usually referred to his visitors as "gentlemen" and sometimes gave their professions or interests, but he seldom wrote their names. In this letter, however, he told exactly who had visited him eight years earlier, King James II (reigned 1685-1688). When he visited Delft in 1679, he was still the Duke of York and his daughter Mary had recently married the Dutch stadhouder.

In 1687, the king was apparently still on Leeuwenhoek's mind. On March 1, he wrote a letter addressed to James that he published in Latin translation as the dedication to Anatomia Seu interiora Rerum later in 1687. In June of that year, when Leeuwenhoek wrote Letter 57, he mentioned the visit again.

I have shown, among other things, also the above-mentioned parts of the louse to his Royal Majesty of Great Britain (when he was lately in these countries, and condescended, and did me the honour, to come to my house to inspect my humble experiments); and I recounted to him the use of the sting, which the louse carries in its abdomen, from which I gave the reason why the soldiers, when drenched with rain, are plagued more by the lice, than in dry weather. Which created much pleasure.

Leeuwenhoek had not hesitated to offer a practical application of his research that would have been relevant to James's position as a military officer.

Response to other researchers

On the plate below, the lower two figures look as though they were drawn by a different hand than the upper eight. Fig. 9 was re-engraved from the recently published Micrographia nova, written in Latin by German researcher Johann Franz Griendel. At the end of Letter 57, Leeuwenhoek wrote:

People have come to talk to me, and sing the praises, of a certain little book, dealing with microscope observations, which were uncommonly magnified, which booklet was sold by auction at the last Frankfort Trade Fair. I was very anxious to have that, as I hoped to get some enlightenment from it.

But no sooner had I received that book, called Micrographia Nova, published by Mr. Joh. Francisco Griendelio, than I saw that it was to me quite worthless: for the small creatures that, amongst others, are depicted therein, as louse, flea, ant, etc., were indeed big, but drawn very imperfectly and deformed. Now whether this is due to the lack of good magnifying-glasses, or whether it is the draughtsman's fault, is not known to me. I have thought fit to get only two legs copied, of the louse, that was in that booklet, to indicate the deformity of the same.

Fig. 9. AB. and CD. are the two legs of the Louse that are found drawn in Micrographia Nova, published by Mr. Joh. Francisco Griendelio, Pag. 14, and which legs were indicated there by I. and C.

He was referring to the drawing on the right. His draughtsman copied the two legs on the upper right, cropped and rotated below left to more easily compare to Leeuwenhoek's Fig. 9. It was not only Griendel's book that had inaccuracies.

I have seen several lice as drawn through the microscope, but they all differ from my own observations. About twelve years ago I sent Your Honour the drawing of a Louse's leg, in order that you might see the perfect shape of such a tiny creature.

However, this Letter 11 of March 26, 1675, written to Henry Oldenburg, had not been published in Philosophical Transactions. Had it been, perhaps Griendel and the others would have been able to learn from it. Fortunatly, Leeuwenhoek wrote:

As I have also found another drawing of it, I have caused this to be printed here as well, in order that one may see the structure of the Louse's leg, as I showed it to the Draughtsman, and which he has drawn from life, against the structure such as they have depicted it in Germany.

This drawing is Fig. 10, which Leeuwenhoek explained in terms of its function:

The big claw that the louse necessarily requires on each leg: For when the same is on a hairless part of the body, he strikes this claw into the outer skin, in order to press the sting (which he carries in his head, and with which he draws the blood from the body) with force into the body.