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1590
Hans and Zacharias Janssen created the compound microscope in the late 16th century after realizing that objects at the other end would be enlarged if a lens was placed at the top and bottom of a tube. Cell observation became more convenient and simple as a result. The original microscope was made up of three draw tubes with lenses at the ends. This microscope was sophisticated for its day. A bi-convex eyepiece lens and a plano-convex objective lens made up the construction. By focusing on the sample and sliding the draw tube in or out, pictures might be magnified. A sample might be magnified up to 10 times its original size when the tubes were at their longest length. The development of this scientific theory laid the foundation for the advancement in microscopy.

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1665

In 1665 Hooke was studying snowflakes and found small objects that made it up. He named these cells. This name is still used today as a major part of science. In 1666 to 1672 he devolped theories on gravity which was then modified by newton. These things caused him to become one of the first father of the theory of evolution. This discovery led to the development of the classical cell theory.

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1674

Anton van Leeuwenhoek created lenses to refine the microscope. He was the first to see microorganisms, for example he was the first to see the nucleus of blood cells. People didn’t accept the term that cells are the building blocks of organisms until Leeuwenhoek proved otherwise.

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1838

The first fundamental idea regarding cells was that all plant tissues are made up of cells. This was brought together by a German botanist and his collaborator, Schwann. Through experiments with plants, he observed that plants were made of cells. These cells showed vegetable tissue development, which was a result of cellular activity. In 1838, Schleiden's research led him to conclude that all living things are made up of one or more cells. Schleiden also proved eukaryotic cells were the starting component of plant embryos. According to him, all plant matter is made up of cells, which are its fundamental building blocks

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1839

Schwann verified the existence of cells and traced the development of many adult tissues from early embryo stages.

He proposed generalizations about the nature of cells: First, animals and plants consist of cells plus the secretions of cells. Second, these cells have independent lives, which, third, are subject to organism’s life.

The phenomena of individual cells can be placed into two classes. Plastic phenomena relate to the combination of the molecules to form a cell. Metabolic phenomena result from chemical changes either in the component particles of the cell itself, or in the surrounding cytoplasm.

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1855

The discovery made by Virchow that contributed towards the cell theory was that only particular cells or cell types might become ill, not the entire organism as a whole. Virchow realized that it was a particular interpretation of the cell. At the age of 34, he wrote the now-famous phrase "omnis cellula e cellula" ("every cell stems from another cell"), which was published in 1855. The theory showed that each cell came from an earlier cell rather than from amorphous material.