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MICROBES, FLEAS, AND THE "VAST CHAIN OF BEING" HOWARD GEST* MICROSCOPE, an optick instrument, contrived various ways to give to the eye a large appearance of many objects which could not otherwise be seen. If the eye were so acute as to rival the finest microscopes, and to discern the smallest hair upon the leg of a gnal, it would be a curse, and not a blessing, to us; it would make all things appear rugged and deformed ; the most finely polished crystal would be uneven and rough; the sight of our own selves would affright us; the smoothest skin would be beset all over with ragged scales and bristly hair. Bentley. MICROSCOPIC. 3. Resembling a microscope. Why has noi man a microscopick eye? For this plain reason, Man is not a fly. Say what the use, were finer opticks given, T'inspect a mite, noi comprehend the heav'n? Pope. FLEA. A small red insect remarkable for its agility in leaping, which sucks the blood of larger animah.—Samuel Johnson, A Dictionary of the English Language [1] During the period 1665 to 1685, the microscope and its revelations of minute living creatures, some unseen by the naked eye, became the rage in scientific and lay circles in England. This was due primarily to the genius of Antoni van Leeuwenhoek (1632—1723). Leeuwenhoek discovered an unknown world of living organisms by examining a great variety of natural materials using simple microscopes of his own design. In 1654, he opened a draper's shop in Delft, Holland, and it has been suggested that use of a low-power magnifying glass to inspect the quality of cloth may have been the starting point of Leeuwenhoek's unique scientific career. He developed the ability to make very small lenses— *Photosynthetic Bacteria Group, Biology Department and Department of History and Philosophy of Science, Indiana University, Bloomington, Indiana 47405.© 1993 by The University of Chicago. AU rights reserved. 003 1 -5982/93/3602-0794$0 1 .00 184 Howard Gest ¦ "Vast Chain of Being" only about 1 millimeter in diameter—of superb quality. The lens was embedded in a small metal sheet (usually about 1x2 inches), and the device was equipped with adjustable screws that could position a sample (for instance, within a very thin glass tube). When held close to the eye, and focused by adjusting the screws, these simple microscopes revealed to Leeuwenhoek clear images of very small objects, magnified as much as 300 times or more. Leeuwenhoek's observations were all described in more than 300 letters , 190 of which were sent to the Royal Society of London. This remarkable shopkeeper, who had little formal education, described for the first time the sperm cells of animals, including humans, and he was also the first person to recognize that in the fertilization process, the sperm enters the egg cell. He provided the first accurate description of red blood cells. At a time when it was widely thought that maggots, fleas, and the like were formed by "spontaneous generation," Leeuwenhoek showed that such creatures hatch from fertilized eggs. The list of "firsts" goes on and on [2]. The reaction to Leeuwenhoek's early letters was that he was either a madman or a fool, but Robert Hooke (1635-1702), the Curator of the Royal Society, introduced microscopic demonstrations at meetings of the Society and confirmed a number of Leeuwenhoek's observations during 1677 and 1678. A recent reminder of Leeuwenhoek's extraordinary skills is owing to interesting findings made by Brian J. Ford [3, 4]. In 1981, Ford was examining the original correspondence of Leeuwenhoek to the Royal Society (kept in their double-locked vaults) and discovered nine packets, attached to letters, that contained sections of biological specimens (of cork, elder-pith, etc.). These were cut by hand by Leeuwenhoek between 1674 and 1687 using a sharp shaving razor. Surprisingly, a number of these sections still gave excellent images in modern microscopes. Ford [4] notes: "Without any doubt these [cork] sections were as good as the best hand-cut sections might be today. The finest parts were only a few micrometres (thousandths of a millimetre) thick, and the detailed structure of the cell walls...

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