Observations through the microscope opened the doors to a previously invisible and unknown world, confirming the existence of microorganisms and producing the first descriptions of cells in plants and animals.

No true cell theory existed in the seventeenth century. That red blood cells were homologous with cells in solid animal tissue was an unknown fact, and no one had inferred that the concept of the “cell” included plant and animal cells, single-cell organisms (such as the protozoa), and sex cells. Moreover, no one understood the functions of the cell, that is, no one knew how cells functioned until the invention of the microscope. [kw]First Microscopic Observations (1660’-1700)
[kw]Microscopic Observations, First (1660’-1700)
Science and technology;1660’-1700: First Microscopic Observations[1990]
Inventions;1660’-1700: First Microscopic Observations[1990]
Health and medicine;1660’s-1700: First Microscopic Observations[1990]
Biology;1660’-1700: First Microscopic Observations[1990]
England;1660’-1700: First Microscopic Observations[1990]
Italy;1660’-1700: First Microscopic Observations[1990]
Netherlands;1660’-1700: First Microscopic Observations[1990]
Microscope
Biology;microscope and
Botany;microscope and

The first compound microscopes Microscope , built in the first half of the seventeenth century, were in widespread use by the 1620’. Microscopes had two or three convex lenses with an average magnification of up to 50 times normal, with the best at 100 times normal. Though single lens magnifying devices such as spectacles and flea-glass lenses existed earlier, it was not until later in the seventeenth century that lens grinders began making single lens microscopes.

Antoni van Leeuwenhoek Leeuwenhoek, Antoni van perfected the single lens microscope with its tiny bead lens and its best magnification of more than 250 times normal in the late 1660’. While the much weaker compound microscopes were easier to use, they were subject to chromic aberrations, a problem not solved until the nineteenth century. The stronger single-lens microscope was much more difficult to use, however, as it had an extremely short focal length often requiring the lens to be placed on the object. Robert Hooke Hooke, Robert and Nehemiah Grew, Grew, Nehemiah and perhaps Marcello Malpighi, Malpighi, Marcello used compound microscopes. Jan Swammerdam Swammerdam, Jan constructed single lens microscopes also, some with lenses as tiny as 1 to 2 millimeters in diameter.

Hooke’s Micrographia: Or, Some Physiological Descriptions of Minute Bodies Made by Magnifying Glasses(1665; better known as Micrographia
Micrographia (Hooke) ), considered to be the first publication to describe cells, marked an advance over earlier microscopic work. Hooke dissected and described not only common things such as glass beads and the edges of a razors (revealing imperfections) but also natural forms such as snowflakes, molds, nettle, hair, and the head of a fly (revealing perfections).

Also, Hooke called “pores” and “cells” those structure he observed in everything from stones to living bodies such as wood, plants, and bones, theorizing that in living bodies, pores conveyed juices. The pores and cells resembled little boxes separated by “diaphragms.” He believed that these cells explained some of the properties of cork, such as its lightness and buoyancy, but the pores of plants such as the carrot, fern, and reed revealed a different arrangement. Hooke also observed pores in a feather shaft. Using the terms “caverns,” “bubbles,” or “cells” to designate the feather-shaft pores, he described what looked more like a froth of tiny bubbles than pores separated by a diaphragm. In plants, the cells were filled with juices, though Hooke could not detect a “passage” to account for the phenomenon of “sweating.” He had hoped to find analogous phenomena in animal vessels.

Grew, author of many papers and several books on plants, studied the anatomy of plant roots, leaves, reproductive parts and products, and their chemical composition, attempting to explain plant nutrition by the circulation of fluids and air. Distinguishing with the naked eye the parenchyma and ligneous tissues, he discovered that a plant’s woody tissues consisted of numerous tiny “vessels” or fibers as well as separate “bubbles” or “bladders” (that is, cells composed of the parenchymatous part).

In Anatome plantarum
Anatome plantarum (Malpighi) (1675, 1679; plant anatomy), Malpighi illustrated the cellular arrangement of herbaceous plants such as portulaca, wheat, chicory, and hemp as well as bark and trees such as the willow and poplar. The word Malpighi used to describe this arrangement was “utriculus” (small bag), for, like Hooke, he believed the individual cell contained fluid. Malpighi is considered, along with Grew, the cofounder of the study of plant anatomy.

Cells within the solid organs of animals were more difficult to detect (lacking the plant’s cell wall), but animal blood would help in the discovery of the animal cell. The first reference to red blood cells appeared in 1665, with Malpighi’s observation of reddish “globules” of fat in the blood vessels of the hedgehog. (The use of the word “fat” illustrates an uncertainty, for microscopists confused fat and blood cells for some time.) Jan Swammerdam also observed red blood cells, which appeared to him also as reddish particles in a clear fluid. The date of Swammerdam’s observation is not certain because his works were undated and were published posthumously by the Dutch physician Hermann Boerhaave as Bybel der naturre (1737-1738; Book of Nature: Or, The History of Insects
Book of Nature (Swammerdam) , 1758).

Marcello Malpighi.

(National Library of Medicine)

Leeuwenhoek made the first definitive description of red blood cells, or “globules,” in 1674, but he used the word “globule” also for particles in milk (fat particles). In a letter to Hooke dated March 3, 1682, Leeuwenhoek observed that the particles in mammalian (including human) blood shared the red color when in a group of three of four cells, and shared the same flat oval shape.

Leeuwenhoek’s next discovery, in 1688, in effect replicated a discovery made by Malpighi in 1661: the existence of capillaries. The two had thus solved a problem concerning the circulation of the blood, which had been proposed by William Harvey Harvey, William . Harvey, however, was been unable to see the “communication” between the veins and arteries that his theory demanded. In 1688 also, Leeuwenhoek observed red blood cells coursing through the capillaries in the tail of a tadpole. In the frog’s gills, the vessels were so thin than only a single corpuscle at a time could flow through them.

Leeuwenhoek also discovered other kinds of cells, including the spermatozoan, animalcules, and bacteria. He discovered animalcules (protozoa such as ciliates and flagellates) in rainwater in 1674 and in a pepper infusion in 1676. Also in 1676, he described an animalcule, which, based on that description as well as his estimate of its size, must have been a free-living bacterium. He observed many other animalcules, including intestinal protozoa and bacteria in human plaque. In 1677, he observed spermatozoa in the semen of a man with gonorrhea.

Scientific interest in microscopy and cell theory began to wane around 1680, though Leeuwenhoek continued to publish in the field until his death in 1723. Cell theory developed in the nineteenth century, however, initiated by the work of Matthias Schleiden (1804-1881) in botany and Theodor Schwann (1810-1882) in physiology.

Seventeenth century microscopy, specifically, is noteworthy for applying the Baconian ideal of empirical science. In the preface to Micrographia, Hooke asserted that it was time for plain observations by scientists to replace “brain and fancy,” and Swammerdam rejected book knowledge in favor of direct observation. The microscope certainly expanded the horizon of observation.

Microscopy also illustrates how mechanical philosophy was applied to subjects beyond physics. For example, Swammerdam advocated a theory of preformationism, that is, that animals were not generated but instead grew from their inception. In addition, Malpighi, Hooke, and Grew attempted to place their findings within contemporaries philosophies of nature.

• Cobb, Matthew. “Reading and Writing ’The Book of Nature’: Jan Swammerdam, 1637-1680.” Endeavour 24 (2000): 122-128. This article, by a noted Swammerdam scholar, describes the biologist’s work.
• Dobell, C. Antony van Leeuwenhoek and His “Little Animals.” London: Bale and Danielsson, 1932. This work contains translations from Leeuwenhoek’s observations of protozoa and bacteria as well as a description of his life. Includes illustrations.
• Ford, Brian J. Single Lens: The Story of the Simple Microscope. New York: Harper, Row, 1985. Ford details the development and use of the microscope from its invention to the nineteenth century. Includes good illustrations.
• 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.
• Harris, Henry. The Birth of the Cell. New Haven, Conn.: Yale University Press, 1999. A short history of the discovery of the cell, covering the seventeenth to the early twentieth 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. Although this book focuses on artist Jan Vermeer’s perception of the world, it describes how that perception was influenced by the microscope and other discoveries in the science of optics. Several chapters describe how seventeenth century scientists created a “more optical” way of viewing the world.
• Piccolino, Marco. “Marcello Malpighi and the Difficult Birth of Modern Life Sciences.” Endeavour 23, no. 4 (1999). Focuses on Malpighi’s contributions to science, including his pioneering work in microscopic medical anatomy, the composition of the human body, and the pathology of diseases.
• Ruestow, Edward G. The Microscope in the Dutch Republic: The Shaping of Discovery. New York: Cambridge University Press, 1996. Ruestow focuses on the work of Swammerdam and Leeuwenhoek, and includes a chapter on the development of the microscope.
• Wilson, Catherine. The Invisible World: Early Modern Philosophy and the Invention of the Microscope. Princeton, N.J.: Princeton University Press, 1995. Wilson discusses theoretical issues that influenced early microscopy, including the preformation-epigenesis dispute and the theory of contagion developed in response to the discovery of infusoria. She examines also the larger philosophical issues of the day, such as the nature of generation.

Galileo; William Harvey; Jan Baptista van Helmont; Robert Hooke; Christiaan Huygens; Antoni van Leeuwenhoek; Hans Lippershey; Marcello Malpighi; Jan Swammerdam; Jan Vermeer. Microscope
Biology;microscope and
Botany;microscope and