1632 – 1723

Microscopes and Bacteria
	"…..my work, which I've done for a long time, was not pursued in order to gain the praise I now enjoy, but chiefly from a craving after knowledge, which I note resides in me more than in most men. And therewithal, whenever I found out anything remarkable, I have thought it my duty to put down my discovery on paper, so that all ingenious people might be informed thereof."
Leeuwenhoek was born in Delft, Holland, on October 24th, 1632, his father was a basket-maker and his mother came from a family of brewers. As a child he was educated in the local school at Warmond and then lived with his uncle at Benthuizen. At the age of sixteen he was apprenticed in a linen-draper's and in 1654 after marrying his first wife, Barbara, returned to his original home in Delft where he remained until his death at the great age of ninety-one. After twelve years of marriage, his wife died, and of their five children, only one survived, his daughter Maria. He did marry again, but it was his daughter, who was his constant support and cared for him for the rest of his life after he was widowed for the second time. On returning to Delft, he started in business as a draper and is also known to have worked as a wine assayer. Although he was not well educated, Leeuwenhoek was highly respected and in 1676 the members of the council governing Delft appointed him trustee of the bankrupt estate of the widow of his friend, the painter Jan Vermeer. At some point before 1668, Leeuwenhoek had learned how to grind lenses. He made simple microscopes and spent many happy hours observing with them. He had been inspired to take up microscopy by acquiring a copy of Robert Hook's illustrated book "Micrographia" which was very popular at that time and showed Hook's own observations with the microscope. Leeuwenhoek lived a comfortable life, he enjoyed his food and drink, his daughter, Maria, cared for him and his dog, horse and talking parrot gave him immense pleasure. However, his work as a draper did not fully occupy him and he began to spend more and more time making microscopes. He would spend hours looking through them at many different objects, the lens of a whale, his own sperm and the manure of his horse. He is known to have made over 500 'microscopes', but less than ten have survived to the present day. In design, these microscopes were simply very powerful magnifying glasses, not compound microscopes as used today. They were simple devices 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 whole instrument was only 3-4 inches long and had to be held close to the eye, requiring good lighting and great patience. Although it has been said that Leeuwenhoek was the inventor of the microscope, this is not the case, as several of his predecessors had built compound microscopes using more than one lens and were making important discoveries with them. However, because of technical difficulties in building them, the early compound microscopes were not practical for magnifying objects more than twenty or thirty times their natural size. Leeuwenhoek's skill at grinding lenses and his excellent eyesight enabled him to build microscopes that were able to magnify items over 200 times. He achieved clearer and brighter images than any of his peers and he was intensely curious to observe absolutely anything that could be put under his lenses. As he was not able to draw well, he hired an illustrator to prepare drawings of the things he saw and his detailed written descriptions, which accompanied the drawings, made the micro-organisms instantly recognisable. In 1673, Regnier de Graff, a Dutch physician and anatomist, wrote a letter to the Secretary of the Royal Society of London, Henry Oldenburg, telling him that a fellow Dutchman had constructed a wonderful microscope through which it was possible to see very tiny objects. Because of de Graff's reputation, Oldenburg invited Leeuwenhoek to submit a letter describing some of his microscopic findings for possible publication in the society's "Philosophical Transactions". This was the start of a fifty-year correspondence with the Royal Society. As he could not speak any other language, Leeuwenhoek's letters were written in Dutch and were translated into English or Latin. Naturally, Leeuwenhoek was flattered by Oldenburg's invitation, although the first paper he submitted was not particularly significant. He described the appearance of common mould as well as the eye, sting and mouth of a bee, as seen on his microscope, descriptions of which had already been published earlier by Robert Hooke, a Fellow of the Royal Society. However, in October 1676 Henry Oldenburg received a seventeen and a half page letter, and after translating it into English, published it in the Society's March 1677 issue of "Philosophical Transactions". In Letter 18 Leeuwenhoek described how he had discovered 'little creatures' in rain that had been standing in a tub for a few days. He investigated his discovery further and saw that "these little animals to my eye were more than ten thousand times smaller than the water-flea or water-louse, which you can see alive and moving in the water with the bare eye". He continued with his microscopic investigations with water from his well and seawater. All these different specimens had been left exposed to the air prior to his examination and the "little animals" particularly fascinated him, with their tiny legs and tails, which allowed them to rush around in tiny drops of water. It was not until he examined water that had been infused with ground pepper that he described microscopic "animals" that were undoubtedly bacteria, but in Letter 18 he did not suspect that his little animals had cousins that have proved to be among man's deadliest enemies. Letter 18 caused a stir amongst the Fellows of the Royal Society, as they could not believe that an uneducated Dutch draper could have made such a momentous discovery. They requested that Leeuwenhoek invite some of the more important local dignitaries to his home and demonstrate his findings so that they could be authenticated to the Society. This, Leeuwenhoek was happy to do and in 1678, Robert Hooke, the Society's own microscopist verified his findings. Two years later Leeuwenhoek was invited to become a Fellow of the Royal Society – the one and only time a haberdasher and part-time janitor would be offered such an honour. In gratitude, over the next fifty years of his membership he submitted more papers than any other Fellow in the three hundred years of the Society's existence. Another important letter to the Royal Society, Number 39, submitted in 1683, was concerned with the observations on his own spittle and the plaque between his front teeth. Although he couldn't see any animals in his spittle, he found thousands of them in the scrapings from the plaque. Later, when he re-examined the scrapings, he was unable to detect any of the little animals. Initially, he was mystified as to where they had gone, but some days later it occurred to him that his scalding coffee must have killed them. He then examined the scraping from his back teeth, which had not been directly exposed to the hot coffee, and there he found thousands of his "animalcules". Without doubt, Leeuwenhoek came close to discovering that his little animals did more than just rush to 'corrupted' flesh and bone, they were responsible for the corruption. He was so close to the germ concept of disease; his reports on the animalcules he found in the scrapings of his own coated tongue when he had a fever and the examination with his microscope of the decay he found after extracting one of his teeth. He also examined the mouth of an old man who had never cleaned his teeth, and there he 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 number, that all the water….seemed to be alive". These were amongst the first observations on living bacteria ever recorded. Leeuwenhoek examined his own faeces and also those of cows, horses and pigeons. Only the dung of horses and cows did not contain his little animals. He studied his own blood and found that it consisted in great part of what we now know as red blood cells and when examined under his microscope, the cells lost their red colour. When he examined his own semen he saw that this too swarmed with little animals, but unlike his findings in rain, seawater or well water, the animalcules in his semen were all alike. The thousands he examined had identical tails and bodies consisting of only a head and they were all swimming around in his seminal fluid. It was several decades before his discovery of the existence of these sperm creatures was accepted. It seems strange that other scientists, who had more sophisticated microscopes available to them fifty years before Leeuwenhoek's simple biconvex lens system, had not discovered the existence of creatures invisible to the human eye. They would only examine an object, however small, which could be seen with the naked eye, for example, the egg of a silkworm or the eye of a louse. They had not appreciated that objects of some kind might exist in liquids such as water, blood and semen that were invisible to the eye alone. Leeuwenhoek looked at animal and plant tissues and at mineral crystals and fossils and his discoveries were many. He became famous as his letters were translated and published. In 1680 he was elected a full member of the Royal Society, joining other legendary scientist 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 curious visitors to his home to see the many strange things he described. He continued with his observations until the end of his life. Several years before his death, Leeuwenhoek made a beautiful wooden cabinet containing a number of shelves to hold twenty-six of his different microscopes, many of which had lenses mounted in silver. Each of the microscopes had specimens permanently secured for ease of viewing, for example, a segment of a hog's tongue, the eye of a flea and a section of a whale's eye. Shortly after his death, his daughter Maria carried out his wishes and sent the cabinet to London, where it remained at the Royal Society for over a century until it disappeared. Over the years, Leeuwenhoek had accumulated two hundred and forty-seven other microscopes and one hundred and seventy-two lenses mounted in gold, silver and brass which Maria put up for auction in 1745; they made just Ł61. After his death in 1723, the Royal Society, and the rest of the world, promptly forgot Leeuwenhoek, including his own townsmen and his country. Thirty-nine year years later, an Austrian, Marc von Plenciz (1705-1781), declared that contagious diseases were caused by the Dutchman's small 'animalcules'. Following this assertion, in 1835 Agostino Bassi (1773-1836) from Lodi in Italy, demonstrated experimentally that silkworm disease was caused by bacteria and he suggested that other diseases might also be caused by bacteria. Finally, after one hundred and twelve years, some of Leeuwenhoek's 'little animals' were identified as the cause of infection and this simple man was rightly identified as the founder of bacteriology and protozoology. British Scientist, Brian J. Ford, has rediscovered some of Leeuwenhoek's original specimens in the archives of the Royal Society of London. His study of these specimens and other material, using Leeuwenhoek's own microscopes and other single-lens microscopes, has shown what an extremely good scientist and craftsman the Dutchman really was. Acknowledgements Medicine's Greatest Discoveries Meyer Friedman, M.D and Gerald W. Friedland, M.D. Leeuwenhoek site

Antony Van Leeuwenhoek