Discovery of Microscopic Life
The discovery of microscopic life marks a significant chapter in the history of science, particularly in understanding the biological world. Beginning in the late sixteenth century, microscopy evolved from a nascent interest into a respected scientific discipline by the mid-seventeenth century. Early contributors like Francesco Stelluti and Giovan Battista Hodierna laid the groundwork with their observations of insect anatomy. However, it was Robert Hooke's 1665 publication of *Micrographia* that famously introduced the concept of the cell as a fundamental unit of life. Antoni van Leeuwenhoek further advanced this field through meticulous lens grinding, enabling him to observe and describe various microscopic organisms, including bacteria and protozoa, starting in the 1670s.
Leeuwenhoek's letters to the Royal Society documented his groundbreaking discoveries, revealing a diverse world of microscopic life previously unseen. His work not only identified these organisms but also highlighted their implications, illustrating the microscopic complexity of life. Both he and Hooke are regarded as foundational figures in microbiology, with Leeuwenhoek's innovations in observational techniques paving the way for future scientific inquiry. While much about these microorganisms remained enigmatic at the time, their discovery underscored the potential of microscopy as a vital tool for scientific exploration, setting the stage for advancements in biology that would unfold in subsequent centuries.
Discovery of Microscopic Life
Locale Delft, Holland, United Provinces (now in the Netherlands)
Date 1672-1684
Leeuwenhoek’s pioneer work in designing, building, and using microscopes and his discoveries of protozoa and bacteria laid the foundation for the modern science of microbiology
Key Figures
Antoni van Leeuwenhoek (1632-1723), Dutch biologist and microscopistPierre Borel (1620?-1671/1689), French physician and botanistRegnier de Graaf (1641-1673), Dutch physician and anatomistNehemiah Grew (1641-1712), English physician and botanistRobert Hooke (1635-1703), English mathematician and general scientistZacharias Janssen (1580-c. 1638), Dutch lens grinder and inventor of the compound microscopeGiovan Battista Hodierna (1597-1660), Italian astronomer, naturalist, and Roman Catholic priestHenry Oldenburg (1619-1677), German-English diplomat and administrator, first secretary of the Royal Society of London, and first editor of its journalPhilosophical Transactions Francesco Stelluti (1577-1646/1652), Italian mathematician and naturalist who coined the term “microscope”Jan Swammerdam (1637-1680), Dutch physician and naturalist
Summary of Event
Microscopy began in the late sixteenth century but did not become widespread and respected among scientists until the middle of the seventeenth century. The first published illustrations of microscopic specimens appeared in 1625, as drawings of parts of bees in Francesco Stelluti’s Melissographia . Giovan Battista Hodierna invented the technique of sectioning anatomical structures for microscopic examination, and he published his studies of sectioned insect eyes in 1644.
Pierre Borel was the first to apply microscopy to medical problems. In 1653, he published his discovery of red blood cells, and in 1655, motivated by historical interest, he traced the origin of microscopy to Zacharias Janssen’s invention of the compound microscope around 1590. Jan Swammerdam recorded his description of red blood cells in 1658 and published the results of his microscopic investigations of insects in 1669.
The most important event in microscopy before Antoni van Leeuwenhoek was the publication in 1665 of Robert Hooke’s magnificently illustrated Micrographia: Or, Some Physiological Descriptions of Minute Bodies Made by Magnifying Glasses (better known as Micrographia ), which announced Hooke’s discovery and naming of the cell as the basic biological structure.
Leeuwenhoek was working as a draper, merchant, and minor government official in Delft when he began grinding lenses sometime between 1668 and 1672. By 1672 his lenses were as powerful as any that then existed. What started as a hobby soon made him famous. Inspired in part by Micrographia, Leeuwenhoek examined all kinds of substances and concoctions, carefully recording his observations in his diary.
In an April 28, 1673, letter to Henry Oldenburg, Regnier de Graaf brought Leeuwenhoek’s work to the attention of the Royal Society of London, then the most prestigious scientific organization in the world. Oldenburg published an excerpt from this letter in Philosophical Transactions of the Royal Society (May 19). As the readers reacted enthusiastically to its descriptions of molds, bees, and lice, Leeuwenhoek followed with a letter to Oldenburg about the legs and stingers of bees (August 15). Part of this letter appeared in the October 6 issue and was accompanied by illustrations. A selection of extracts from these letters was published by the society as A Specimen of Some Observations Made by a Microscope (1673). Thereafter, Leeuwenhoek was a popular and frequent contributor to the journal.
Excerpts from Leeuwenhoek’s letters of August 15, 1673, and April 7, 1674 (pb. April 27), and from his letters of June 1 and July 6 (pb. September 21), dealt with microscopic aspects of blood, hair, milk, saliva, brain tissue, bone, and other animal components. The subject matter of his September 7, 1674, letter (pb. November 23, 1674) was similar, but the last paragraph described his examination of water from Lake Berkel. Leeuwenhoek wrote, “among all which there crawled abundance of little animals . . . some of these little creatures were above a thousand times smaller than the smallest ones, which I have hitherto seen. . . .” This was the first mention in any scientific literature of independent unicellular life and probably referred to the alga spirogyra and some species of protozoa.
Leeuwenhoek’s undated letter (pb. September 26, 1675) reported his observations of the optic nerve, blood, sugar and salt crystals, and plant sap. Increasingly encouraged throughout the 1670’s by Nehemiah Grew, Leeuwenhoek turned more attention toward botanical phenomena. His April 23, 1676, letter (pb. July 18) concerned mostly plant life and mentioned Grew several times, but it also recounted his finding in wine “small living Creatures, shaped like little eels.”
Leeuwenhoek’s most celebrated contribution to the Royal Society was his letter of October 9, 1676, “Concerning Little Animals by Him Observed in Rain- Well- Sea- and Snow- Water; as Also in Water Wherein Pepper Had Lain Infused” (pb. March 25, 1677). Here he described “animalcula or living Atoms,” reported that he had first noticed them in standing rainwater in 1675, and provided clear measures of their tiny size. Most of the creatures depicted in this letter were protozoa, but at least one type was a bacterium. In stagnant pepper water that was still for several days, he saw “incredibly small” animals that he computed were each smaller than one-millionth of a grain of sand. This was the first published mention of bacteria. Leeuwenhoek’s March 23, 1677, letter (pb. April 23) answered some questions and clarified some points about these various “little animals.”
In 1677 and 1678, Hooke confirmed Leeuwenhoek’s results by reproducing several of these experiments with protozoa in water infusions. While doing this, Hooke may have been the second scientist to see bacteria. He wrote privately to Leeuwenhoek in December of 1677 of having seen through the microscope what appeared to be “gygantick monsters in comparison of a lesser sort which almost filled the water.” The former were certainly protozoa, and the latter were likely bacteria.
Although Leeuwenhoek probably discovered bacteria in 1676, the earliest published illustrations of these findings did not appear until his letter of September 17, 1683 (pb. May 20, 1684). This letter included the first specific descriptions and drawings of the round, rod-shaped, and spiral forms of bacteria, which later scientists named cocci, bacilli, and spirochaeta respectively.
Observing bacteria and protozoa was just a small part of Leeuwenhoek’s scientific project. After 1677, the “little animals” under his lens were mostly spermatozoa. His letters published from 1683 to 1685 show more interest in salts, minerals, the anatomy of the eye, and spermatozoa than in protozoa and bacteria. He remained a hobbyist and seemed content to let others delve more deeply into his discoveries, although few did during his lifetime.
Leeuwenhoek believed that his greatest accomplishment was being elected a fellow of the Royal Society in 1680. Even though he knew no language other than Dutch, his correspondence to Oldenburg and subsequent secretaries of the Royal Society was always warmly received, and much of it was duly translated into English and quickly published.
Significance
Along with Hooke, Leeuwenhoek can be considered the founder of microbiology. In his long and fruitful career, he discovered protozoa, bacteria, spermatozoa, and the crystalline lens of the eye. He gave the first accurate descriptions of red blood cells and many other basic components of life, and he invented the technique of staining microscopic specimens to better observe their features. Although the function and physiology of most of the living structures that Leeuwenhoek saw would not begin to be understood until the nineteenth century, he proved in his own time the indispensability of the microscope for science in general and underscored the importance of using the most powerful lenses available, in the best possible light, and with the keenest attention to observed detail.
Bibliography
Dobell, Clifford, ed. Antony van Leeuwenhoek and His “Little Animals”: Being Some Account of the Father of Protozoology and Bacteriology and His Multifarious Discoveries in These Disciplines. New York: Dover, 1960. A reprint of the standard 1932 edition of a richly annotated selection of Leeuwenhoek’s most important works in English, including a much fuller text of the famous October 9, 1676, letter that appeared in Philosophical Transactions.
Ford, Brian J. The Leeuwenhoek Legacy. London: Farrand, 1991. A meticulous scholarly study based on research in the archives of the Royal Society.
Ford, Brian J. Single Lens: The Story of the Simple Microscope. New York: Harper & Row, 1985. A history of the development and use of the simple microscope from the period before Leeuwenhoek’s discoveries through the nineteenth century. More than half of the book is devoted to Leeuwenhoek.
Fournier, Marian. The Fabric of Life: Microscopy in the Seventeenth Century. Baltimore: Johns Hopkins University Press, 1996. Examines the work of Leeuwenhoek and four other scientists to explain the reasons for the microscope’s appearance and eventual eclipse in the seventeenth century.
Gest, Howard. Microbes: An Invisible Universe. Washington, D.C.: ASM Press, 2003. A history of microbiology from the time of Leeuwenhoek to the beginning of the twenty-first century.
Hooke, Robert. Micrographia: Or, Some Physiological Descriptions of Minute Bodies Made by Magnifying Glasses with Observations and Inquiries Thereupon. 1665. Reprint. New York: Dover, 1961. Contains the original observation on cork and many other objects. This work is characteristic of the new philosophy of observation.
Huerta, Robert D. Giants of Delft: Johannes Vermeer and the Natural Philosophers, the Parallel Search for Knowledge During the Age of Discovery. Lewisburg, Pa.: Bucknell University Press, 2003. This work shows the symbiotic relationship between art and science as exemplified in the work of Leeuwenhoek and of Dutch artist Vermeer.
Leeuwenhoek, Antoni van. The Select Works of Antony van Leeuwenhoek: Containing His Microscopical Discoveries in Many of the Works of Nature. Translated by Samuel Hoole. New York: Arno Press, 1977. A relatively easy introduction to a complicated body of primary source material.
Mansuripur, Masud. “The van Leeuwenhoek Microscope.” In Classical Optics and Its Applications. New York: Cambridge University Press, 2002. This chapter situates Leeuwenhoek’s contribution within the wider context of the history of microscopy.
Ruestow, Edward Grant. The Microscope in the Dutch Republic: The Shaping of Discovery. New York: Cambridge University Press, 1996. Ruestow compares the work of Swammerdam and Leeuwenhoek and relates both scientists to their contemporary culture.