What Did Zacharias Janssen Contribute to Microbiology?

Zacharias Janssen, probably with assistance from his father Hans, is credited with the invention of the compound microscope. By introducing a device that increased the ability to see tiny living things, Janssen helped to open up the world of microorganisms to direct study. Within a century of its invention in 1595, scientists such as Robert Hooke and Marcello Malpighi were making significant discoveries using more powerful versions of Janssen’s invention.

Zacharias Janssen was born in 1580 in Holland. He and his father worked as eyeglass makers in Middleburg during a time when eyeglasses were becoming very popular. Another optical scientist, Hans Lippershey, lived nearby and is sometimes credited with the invention of the microscope. However, Dutch diplomat William Boreel, a longtime acquaintance of Janssen, had received letters from Janssen describing the microscope and later observed it firsthand. Though Janssen died in 1638, when the French Royal physician inquired about the origin of the microscope in the 1650s, Boreel provided him with the information from Janssen.

Boreel described a microscope that sat upon a brass tripod fashioned to resemble dolphins. The device was about 2.5 feet long and consisted of a main brass tube between 1 and 2 inches wide with a lens at each end. The use of two lenses is the hallmark of a compound microscope. Janssen improved the original design with two additional tubes that could slide within the main tube. One of movable draw tubes served as an eyepiece with a bi-convex lens, while the lower tube, the objective, had a plano-convex lens. The microscope could magnify objects from three to nine times actual size, depending on how the observer positioned the two draw tubes.

Robert Hooke was one of the preeminent scientists of the 17th century. He made discoveries in many scientific fields and devised a more modern version of Janssen’s compound microscope. In 1665, Hooke published his book, “Micrographia,” containing drawings of various organisms and living structures, from insects to bird feathers. While studying thin cross-sections of cork, Hooke discovered plant cells, and directly observed the cell walls of cork. He then studied cells in other plants. Microscope builder Antony van Leeuwenhoek was the first to observe and accurately describe single-celled microorganisms. Hooke became aware of the discovery of these “little animals” -- protozoa and bacteria -- in 1678 and subsequently confirmed van Leeuwenhoek’s discoveries. Hooke was the first person to study fossils under the microscope and concluded that living tissue could turn into stone over time.

The field of microbiology deals with the study of organisms too small to be seen with the naked eye. Before the development of microscopes, the structure of tiny creatures such as bacteria, viruses, algae, and fungi was unknown. In this sense, Zacharias Janssen can be considered one of the enablers of microbiology. In the 17th century, the microscope helped to disprove spontaneous generation -- the development of life from non-living matter -- by showing the presence of maggot eggs in decaying meat. Modern compound microscopes can magnify objects by 1,000 to 2,000 times, and more advanced magnification devices such as the scanning electron microscope can see objects on the molecular and atomic scales. Microbiology has developed many specialties, including ones relating to medicine, public health, food, agriculture, and industry.