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Anthonie van Leeuwenhoek (Engels)

Geschiedenis

Biografie

5.3 / 10
3e klas vwo

Biography Anthonie van Leeuwenhoek

Anthonie van Leeuwenhoek was an unlikely scientist and naturalist. A tradesman of Delft, Holland, he came from a family of tradesmen, had no fortune, received no higher education or university degrees, and knew no languages other than his native Dutch. This would have been enough to exclude him from the scientific community of his time completely. Yet with skill, diligence, an endless curiosity, and an open mind free of the scientific dogma of his days, Leeuwenhoek succeeded in making some of the most important discoveries in the history of biology. It was he who discovered bacteria, sperm cells, blood cells, microscopic nematodes and rotifers, and much more. His researches, which were widely circulated, opened up an entire world of microscopic life to the awareness of scientists.
Leeuwenhoek was born in Delft on October 24, 1632. His father was a basket-maker, while his mother's family were brewers. Anthonie was educated as a child in a school in the town of Warmond, then lived with his uncle at Benthuizen; in 1648 he was apprenticed in a linen-draper's shop. Around 1654 he returned to Delft, where he spent the rest of his life. He set himself up in business as a draper (a fabric merchant); he is also known to have worked as a surveyor, a wine assayer, and as a minor city official. In 1676 he served as the trustee of the estate of the deceased and bankrupt Johannes Vermeer, the famous painter, who had been born in the same year as Leeuwenhoek and who was a friend of him. Probably around 1668 Anthonie van Leeuwenhoek learned to grind lenses, made simple microscopes, and began observing with them. He seems to have been inspired to take up microscopy by having seen a copy of Robert Hooke's illustrated book Micrographia, which depicted Hooke's own observations with the microscope and was very popular.

Leeuwenhoek is known to have made over 500 microscopes, of which fewer than ten have survived to the present day. In basic design, probably all of Leeuwenhoek's instruments certainly all the ones that are known were simply powerful magnifying glasses, not compound microscopes of the type used today. A drawing of one of Leeuwenhoek's microscopes is shown at the bottom of page six. Compared to modern microscopes, it is an extremely simple device, using only one lens, mounted in a tiny hole in the brass plate that makes up the body of the instrument. The specimen was mounted on the sharp point that sticks up in front of the lens,


and its position and focus could be adjusted by turning the two screws. The entire instrument was only 3-4 inches long, and had to be held up close to the eye; it required good lighting and great patience to use.

Compound microscopes (that are, microscopes using more than one lens) had been invented around 1595, nearly forty years before Leeuwenhoek was born. Several of Leeuwenhoek's predecessors and contemporaries, notably Robert Hooke in England and Jan Swammerdam in the Netherlands, had built compound microscopes and were making important discoveries with them. These were much more similar to the microscopes in use today. Although Leeuwenhoek is sometimes called "the inventor of the microscope," he was no such thing!!
However, because of various technical difficulties in building them, early compound microscopes were not practical for magnifying objects more than about twenty or thirty times natural size. Leeuwenhoek's skill at grinding lenses, together with his naturally acute eyesight and great care in adjusting the lighting where he worked, enabled him to build microscopes that magnified over 500 times, with clearer and brighter images than any of his colleges could achieve. What further distinguished him was his curiosity to observe almost anything that could be placed under his lenses, and his care in describing what he saw. Because van Leeuwenhoek himself could not draw well, he hired an illustrator to prepare drawings of the things he saw, to accompany his written descriptions. Most of his descriptions of microorganisms are instantly recognizable.
In 1673, Leeuwenhoek began writing letters (to the newly formed Royal Society of London, describing what he had seen with his microscopes), his first letter contained some observations on the stings of bees. For the next fifty years he corresponded with the Royal Society; his letters, written in Dutch, were translated into English or Latin and printed in the Philosophical Transactions of the Royal Society, and often reprinted separately. To give some of the flavour of his discoveries, we present extracts from his observations, together with modern pictures of the organisms that Leeuwenhoek saw.
In a letter of September 7, 1674, Leeuwenhoek describes an observations on lake water, including an excellent description of the green charophyte alga Spirogyra: “Passing just lately over this lake, . . . and examining this water next day, I found floating therein divers earthy particles, and some green streaks, spirally wound serpent-wise, and orderly arranged, after the manner of the copper or tin worms, which distillers use to cool their liquors as they distil over. The whole circumference of each of these streaks was about the thickness of a hair of one's head. . . all consisted of very small green globules joined together: and there were very many small green globules as well.”
A letter dated December 25, 1702, gives descriptions of many protists, including this description: “In structure these little animals were fashioned like a bell, and at the round opening they made such a stir, that the particles in the water thereabout were set in motion thereby. . . And though I must have seen quite 20 of these little animals on their long tails alongside one another very gently moving, with outstretched bodies and straightened-out tails; yet in an instant, as it were, they pulled their bodies and their tails together, and no sooner had they contracted their bodies and tails, than they began to stick their tails out again very leisurely, and stayed thus some time continuing their gentle motion: which sight I found mightily diverting.”
On September 17, 1683, Leeuwenhoek wrote to the Royal Society about his observations on the plaque between his own teeth, “a little white matter, which is as thick as if 'twere batter.” He repeated these observations on two ladies (probably his own wife and daughter), and on two old men who had never cleaned their teeth in their lives. Looking at these samples with his microscope, Leeuwenhoek reported how in his own mouth: “I then most always saw, with great wonder, that in the said matter there were many very little living animalcules, very prettily a-moving. The biggest sort. . . had a very strong and swift motion, and shot through the water (or spittle) like a pike does through the water. The second sort. . . oft-times spun round like a top. . . and these were far more in number." In the mouth of one of the old men, Leeuwenhoek found "an unbelievably great company of living animalcules, a-swimming more nimbly than any I had ever seen up to this time. The biggest sort. . . bent their body into curves in going forwards. . . Moreover, the other animalcules were in such enormous numbers, that all the water . . . seemed to be alive.” These were among the first observations on living bacteria ever recorded.
Leeuwenhoek looked at animal and plant tissues, at mineral crystals and at fossils. He was the first to see microscopic foraminifera, which he described as “little cockles. . . no bigger than a coarse sand-grain.” He discovered blood cells, and was the first to see living sperm cells of animals. He discovered microscopic animals such as nematodes and rotifers. The list of his discoveries goes on and on. Leeuwenhoek soon became famous as his letters were published and translated. In 1680 he was elected a full member of the Royal Society, joining Robert Hooke, Henry Oldenburg, Robert Boyle, Christopher Wren, and other scientific luminaries of his day although he never attended a meeting. In 1698 he demonstrated circulation in the capillaries of an eel to Tsar Peter the Great of Russia, and he continued to receive visitors curious to see the strange things he was describing. He continued his observations until the last days of his life. After his death on August 30, 1723, the pastor of the New Church at Delft wrote to the Royal Society:
Anthonie van Leeuwenhoek considered that what is true in natural philosophy can be most fruitfully investigated by the experimental method, supported by the evidence of the senses; for which reason, by diligence and tireless labour he made with his own hand certain most excellent lenses, with the aid of which he discovered many secrets of Nature, now famous throughout the whole philosophical World.

The first microscope

The quality of van Leeuwenhoek’s so called first microscope was far superior if you look at other microscopically design over 170 years from different naturalists.
As a matter of fact, the design of the “simple microscope” of van Leeuwenhoek was nothing more than a lens of amazing quality in a holder.
But what made his microscope so different from others?
The lens quality of the magnifying glasses was often poor due to airbubbles, so the images were not very clear. Most made the suggestion that van Leeuwenhoek had grind and polished his lenses with very small pieces of glass, some others mentioned that he used abrasive powders. But it was also his method of glass-blowing that made his lenses so superior. It was a method probably adopted from Robert Hooke and Johannes Hudde.
Due to his interest in the study of Natural History, van Leeuwenhoek started to grind lenses himself and constructed his own microscopes. His microscopes which he crafted himself by hand had powers of magnification ranging from 50X to 300 X and some of his "sharp-sighted high quality" microscopes probably could reach magnifications of about 500 X.
In several studies of some of his original microscopes, a resolution as good as one micron (1/1000) could be established. The focal distance of the lens in a van Leeuwenhoek microscope of superior quality should be under the one millimetre.

The lens thicknesses of his microscopes are under the two millimetres.
Eventhough that Anthonie van Leeuwenhoek only made and used single lens microscopes with extremely short focal lengths made him see bacteria, which he so called "little animals", spermcells and the very little globules (i.e. chloroplasts) in the green leaves for the first time in history. To observe these objects with this simple microscope, the apparatus has to be placed closely before the eye in vertical position, against the light. He improved the resultant image by taking advantage of the optical principle that the least light distortion occurs close to the central ray.

The magnification of the simple microscope is defined by the formula:

(M stands for magnification, f = focal distance of the lens, point of the normal eye = ± 250 mm)

The object to be examined was raised or lowered and rotated upon its axis by a coarse-threaded-screw. Mister Meyer speculates that Leeuwenhoek's hand-held microscopes were only fit for demonstration purposes and that for his researches, van Leeuwenhoek used a compound microscope, which he kept secret and was lost after his death.
To select the parts of his study-objects he was interested in, van Leeuwenhoek first used a magnifying mirror, then he used a “common” microscope or a magnifying-glass and if not satisfied, he took one of his sharp-sighted microscopes or another way of observing, namely through a more magnifying microscope.
Most of his 500 microscopes were made of silver, gold or copper or brass. His lenses were made of crystal, quartz of even scratch resistant diamond. He never published the way of how to make his lenses, so unfortunately he carried this secret with him to the grave.
He did not make his drawings himself but he instructed his Scriba or Tekenaer or limner carefully how to draw the things he observed and either approved or rejected those drawings. The identity of these limners is uncertain, though in a letter (april 4th, 1687), van Leeuwenhoek gave the following information about his limner:
“To observe the thickness of the canals in a tooth, I handed my limner (who is a copperplate engraver),the magnifying glass and ordered him to draw the things he could see without me telling him what is was.”
These engravings were made on copperplates.
Anthonie van Leeuwenhoek used a saffron-coloring procedure to enhance contrast in his objects. Furthermore, he sometimes filled a small glasstube with clean water containing living material and fixed the tube with the aid of two silver springs onto his microscope-plate. Probably this method caused some extra magnifying effect, due to the greater refraction-index of the water in the glasstube.
To investigate an object, he used different microscopes of his own but sometimes also microscopes of other naturalists. He used a sophisticated design from Johan van Musschenbroek because the microscope had an adjustable fine focus.
Another microscope is called the Aalkijker and van Leeuwenhoek used it to study the blood-circulatory system in the tail of an eel (which was filled up with water in a glass-tube). After a long series of experiments (starting from 1683 up to 1688) van Leeuwenhoek was the first to proof that the bloodcirculatory system was a closed system and that the pulsations were caused by the heart-rhythm.

The theory of the Generatio Spontane (Aristotle, Vergil) predicts that living creatures can be originated from inanimated material. It doesn’t say that living creatures could originate from spoiled meat or dirty laundry.
The doctrine of the Spontanous Generation was accepted without question until the Renaissance.
On the otherhand, van Leeuwenhoek believed that “those animalcules” were formed from the “seeds”or “germs” of these animalcules, which were always present in the air. Even Louis Pasteur did not deny the existence of the Spontaneous Generation : Under experimental conditions he showed that the Spontaneous Generation could not be proved.

Concept of fertilisation

Leeuwenhoek discovered spermcells in November 1677 and published his observations between 1678-1717
Van Leeuwenhoek and his followers believed in the concept that:
The mother serves only as an incubator for the spermazoids and that all characteristics are inherited from the father.
Eventhough that another naturalist (Reinier de Graaf) suspected that the female egg was an entire human in miniature and that the male sperm only stimulated its growth.
He also suspected that all characteristics are inherited from the mother.
Most people agreed with van Leeuwenhoek of course because at that time it was highly inappropriate that everybody came from females.

We know today that neither the egg nor the spermatozoon contains a complete or developed embryo. However, in the second half of the 19th century it was recognised that both the role of the egg and the sperm are equivalent. On several pages in his work van Leeuwenhoek observed both the germination of plants as well as that of animals and their sexual organs, he stepped on to a different concept. Especially when he was observed twins, the offspring from a white male and a coloured woman or the crossbreeding between a horse and a donkey, he had his doubts. Eventhough it was his own speculation of which he was hesitating.
In one of his letters which he wrote to Leibnitz, he mentioned that he specifically researched different kinds of spermcells: males or females, dependent on their size and motility, even from different animals.
Van Leeuwenhoek even hesitated about placing a fertilized egg into the uterus of another female animal to see the influence of the mother.

Before he was chosen as a member of the Royal Society van Leeuwenhoek wrote a letter to William Bounker of the Royal Society in which he showed pictures of spermcells of a human and a dog. At the suggestion of the medical student Johan Ham at Leiden, Leeuwenhoek examined seminal fluid and observed spermatozoa. In 1677, Johan Ham, brought him a specimen of semen in which Ham himself had found small animals with tails, which Leeuwenhoek now observed as well.
Ham brought him spontaneously discharged semen of a man who had lain with an unclean woman and was suffering from gonorrhoea." But, Ham thought that these sperm cells were not a normal part of the sperm

Leeuwenhoek resumed his own observations and in his own semen he observed a multitude of animalcules, (at first he called them "Levende Dierkens") less than a millionth the size of a coarse grain of sand and with thin, transparent tails. He drew the conclusion that the tails must be operating by means of muscles. Van Leeuwenhoek estimated that 27,000,000 of these animalcules equalled a grain of sand, which seems minuscule compared with the germs in each egg.
Some scholars abusively think van Leeuwenhoek was convinced that man was preformed in them or that he thought they were human larvae, but van Leeuwenhoek only declared to observe muscles and nerves in those cells that have a long tail. A long running debate with the Harveian school started from that time on.

Sources

http://encarta.msn.com/encyclopedia_761566325/Anton_Van_Leeuwenhoek.html

http://zygote.swarthmore.edu/fert1a.html

http://www.euronet.nl/users/warnar/leeuwenhoek.htm

www.google.nl and www.altavista.com for pictures

http://www.euronet.nl/users/warnar/leeuwenhoek.htm

http://nl.wikipedia.org/wiki/Antoni_van_Leeuwenhoek

http://www.bbc.co.uk/history/historic_figures/leeuwenhoek_antonie_van.shtml

Encyclopaedia from school pages 27,28 part L

Book: Johannes Vermeer (Waanders uitgevers), Johannes Vermeer was a close personal friend of van Leeuwenhoek.

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