Andreas Gavalas

Events

Hans and Zacharias Janssen

1595

Hans and Zacharias produced the first compound microscope by combining two convex lenses within a tube.Jansen's microscope consisted of three draw tubes with lenses inserted into the ends of the flanking tubes. The eyepiece lens was bi-convex and the objective lens was plano-convex, a very advanced compound design for this time period. Focusing of this hand-held microscope was achieved by sliding the draw tube in or out while observing the sample. The Jansen microscope was capable of magnifying images approximately three times when fully closed and up to ten times when extended to the maximum. No early models of Janssen microscopes have survived, but there is a candidate housed in the Middleburg Museum in the Netherlands that some historians attribute to Jansen. Though rudimentary when compared with modern microscopes, the Jansen microscope was an important advance from single lens magnification. By the end of the seventeenth century, further developments, notably by Anton van Leeuwenhoek and Robert Hooke allowed the observation of organisms such as fossils, diatoms, as well as the first cells.

Robert Hooke

1665

Robert discovered the cellular composition of cork and introduced the word cell to science. thin cutting of cork he discovered empty spaces contained by walls, and termed them pores, or cells. The term cells stuck and Hooke gained credit for discovering the building blocks of all life. He recorded all of his observations in something called Micrographia: or Some Physiological Descriptions of Miniature Bodies Made by Magnifying Glasses.

Anton van Leeuwenhoek

1674

He improved magnification of microscopes by polishing lenses, by placing the middle of a small rod of soda lime glass in a hot flame, van Leeuwenhoek could pull the hot section apart like taffy to create two long whiskers of glass. By then reinserting the end of one whisker into the flame, he could create a very small, high-quality glass sphere. These glass spheres then became the lenses of his microscopes, with the smallest spheres providing the highest magnifications. Basic in design, van Leeuwenhoek's instruments consisted of simple powerful magnifying glasses, rather than the compound microscopes (microscopes using more than one lens) of the type used today or in Zacharias Jansen's original microscope design. Compared to a modern microscope, van Leeuwenhoek's design is extremely simple, using a single lens mounted in a tiny hole in a brass plate that makes up the body of the instrument. The specimen was then mounted on a sharp point that sticks up in front of the lens. Its position and focus could be adjusted by turning the two screws. The entire instrument was only 3-4 inches long, and had to be held up close to the eye, requiring good lighting and great patience to use.

Anton van Leeuwenhoek

1676

Anton discovered animacules or protozoa. He likely observed protozoa for the first time bacteria. Those “very little animalcules” he was able to isolate from different sources, such as rainwater, pond and well water, and the human mouth and intestine. He also calculated their sizes.

Anton van Leeuwenhoek

1683

In 1683 Leeuwenhoek discovered bacteria in water. The bacteria were at the limit of observation of his microscope – he estimated that it would take more than 10,000 of them to fill the volume of a small grain of sand. Such was the brilliance of his work that nobody else observed bacteria until another century had passed.

Matthias Schleiden

1838

Schleiden discovered the plants were made up of cells. Schlieden investigated plants microscopically and conceived that plants were made up of recongnizable units, or cells. Plant growth, he stated, came about through the production of new cells, which, he speculated, where prophagates from the nuclei of old cells. Although later discoveries proved him wrong about the role of the nucleus in mitosis, or cell division, his conception of the cell as the common structural unit of plants had the profound effect of shifting scientific attention to living processes as they happened on the cellular level-a change that initiated the field of embryology.

Theodor Schwann

1839

Theodor Schwann, a German biologist, reached the same conclusion as Schleiden about animal tissue being composed of embryonic cells, ending speculations that plants and animals were fundamentally different in structure. Schwann described cellular strucures in animal cartilage (rigid extracellular matrix).

Rudolph Virchow

1855

Rudolph Virchow : Omnis cellula e cellula, or all cells develop only from existing cells( cells only formed from the division of other cells).