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Designed his own light microscope. (The Editors of Encyclopedia Britannica, 2024)

Used wood, glass, and brass to develop the design.

Grounded glass multiple times to achieve the desired thickness of the lens.

1665: Hooke examines slices of cork, which he describes as cells. (The Editors of Encyclopedia Britannica, 2024)

He first noticed their hexagonal shape, which was later discovered to be the cell wall of the cork cell.

The name of "cells" was coined by Hooke from inspiration of the small rooms where monks reside.

In reality, his discovery was the phenomenon of plant cells.

Hooke's research led to the foundation of cell theory due to his observations during research and his inventions. His observation of the small cells in cork helped lead to the understanding of cells being the smallest units of life, because he was the first to view the basic unit of a plant cell. His creation and usage of the light microscope also contributed to developing this tenet.

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1801: Jean Baptiste Lamarck formulates a full theory explaining the evolution of cells. (Corbis, 2019)

He proposes the idea that simple cells become more complex through the phenomenon of spontaneous generation. (He believed spontaneous generation caused environmental pressures which led to the evolution of cells.)

Spontaneous generation: The idea of living organisms being produced from nonliving matter.(Corbis, 2019)

Eventually was proved incorrect by Louis Pasteur's experiment which disproved spontaneous generation. (Corbis, 2019)

However, his idea that cells developed from simple to complex organisms was proven correct later on.

He also believed that cells modify their behaviors after experiencing a change in their environment. (Corbis, 2019)

Lamarck also constructed the idea regarding the characteristics of an individual being inherited from the traits their parents obtained. (Corbis, 2019)

Lamarck contributed to the third tenet of cell theory. Most of his work was focused on the evolution of cells, and the idea of spontaneous generation. This phenomenon explains how cells are always produced from other living organisms, which is included in the third tenet. Larmarck first proposed that cells would evolve and produce spontaneously due to environmental pressures, but was later proved incorrect. This influenced the creation of the third tenet of cell theory.

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1855: Virchow concludes all cells come from preexisting cells. (Schultz, M., 2008)

Proposes from this discovery that all diseases cause changes to the original state of cells.

He adds to this idea by discovering later on that an entire organism does not become diseased, only detained cells or groups of cells.

Virchow also discovered the cells in bones and connective tissues. (Schultz, M., 2008)

He additionally studied parasitic worms to further his research in disease and illness. (Schultz, M., 2008)

Establishes the concept of zoonosis: Diseases transmitted from animals to humans. (Schultz, M., 2008)

Virchow mainly advanced the third tenet of cell theory. This tenet explains how all cells come from preexisting cells. His research was mainly focused on diseases transmitted through cells. He understood that diseases became more severe from reproduction of cells via preexisting cells.

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1838: Matthias Schleiden and Theodore Schwann

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1838: Matthias Schleiden and Theodore Schwann

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1838: Schleiden and Schwann propose the theory that all plants and animals are made up of cells. (Alberts, B. M., 2024)

Additionally, they both proposed the idea of a single cell being classified as the basic structural unit of all tissues. (Alberts, B. M., 2024)

Specifically, the each studied muscle and nerve tissues in order to propose the unified cell theory. (Owecki, M. K., 2021)

Recognized the common features of the cells to be the nucleus, the cell membrane, and the cell body. (Owecki, M. K., 2021)

Each of them compared these structures in both plant and animal cells. (Alberts, B. M., 2024)

Their discoveries regarding basic cell structure are reflective of the cell theory and biological advancements regarding structural components of cells today. (Alberts, B. M., 2024)

Both Schleiden and Schwann contributed to the second tenet of cell theory, which states that cells are the basic units of structure and function in all organisms. They furthered this tenet by observing the similarities and differences in plant and animal cells. These key factors helped to understand why and how plants and animals function differently. (Difference in organelles and composition.)

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1858: Louis Pasteur disproves spontaneous generation. (Libretexts, 2024)

Spontaneous Generation: The hypothetical process by which living organisms develop from nonliving matter. (Libretexts, 2024)

He formed multiple experiments in order to disprove this idea. (Libretexts, 2024)

Pasteurs Experiment: Different flasks

Broth was boiled in two types of flasks.

S-shaped neck

Broken neck

Result:

The flask with the broken neck became cloudy from the exposure to the outside.

The flask with the S-shaped neck stayed clear.

Conclusions:

His experiment showed that the microorganisms in the broth come from the atmosphere outside the flask and do not arise spontaneously.

When the S-shaped flask was tilted, the appearance became cloudy.

Pasteur contributed to the third tenet of cell theory. His work on disproving spontaneous generation explained how cells can only be produced from preexisting cells. The controlled experiment conducted only yielded cloudy appearance when the opening of the flask was exposed to the outside atmosphere. This advances the development of the third tenet.

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1937: James Hillier and Albert Prebus assemble a microscope which can magnify up to 7000 times the size of an object. (Lemelson, n.d.)

This new and efficient invention was named the electron microscope, due to the mechanism of the tool.(Lemelson, n.d.)

The machine passes a beam of electrons through the microscope rather than a beam of light.

This increases visibility by using a focused beam of electrons, which have a shorter wavelength than visible light.

This allows for a much higher resolution and a clear, high quality visual.

From this, he curated major contributions to electron microscopy and furthered cell theory. (Lemelson, n.d.)

Hillier and Prebus both furthered the first tenet of cell theory, explaining how all living things are made of one or more cells. Their production of the electron microscope allowed scientists to increase their understanding of cell structure and quantity in living organisms. The focused beam of electrons contain a shorter wavelength in comparison to the beam of photons previously used in the light microscope. This creates a clearer and more precise image, increasing discoveries related to cell theory.

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1668: Francesco Redi performs experiments with maggots. (Helmenstine, 2018)

One of his experiments: Maggots and meat (Helmenstine, 2024)

3 flasks each contain meat.

Control group: Open flask containing meat.

Experimental groups:

Cork sealed flask containing meat.

Gauze covered flask containing meat.

His prediction:

Covered flasks will result in no maggots being produced.

Conclusions:

Each flask attracted flies due to smell of the meat. However, the open flask resulted in the production of maggots in the meat. The gauze covered flask had maggots sitting on the cover, while the cork sealed contianer had no maggots whatsoever.

From this, Redi was able to conclude that the maggots were produced from the flies and not spontaneously.

This discovery contributed to the cell theory by developing the tenent stating that all cells come from preexisting cells. It was observed in the experiment that the maggots were reproduced by the flies, which are living organisms. Therefore, his experiment advanced the 3rd tenent of cell theory. (Helmenstine, 2024)

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Francesco Redi was an Italian naturalist, physician, and poet. Besides Galileo, he was one of the most important scientists who challenged Aristotle's traditional study of science. Redi gained fame for his controlled experiments. One set of experiments refuted the popular notion of spontaneous generation -- a belief that living organisms could arise from nonliving matter. Redi has been called the "father of modern parasitology" and the "founder of experimental biology".

Here is a brief biography of Francesco Redi, with particular emphasis on his contributions to science:

Born: February 18, 1626 in Arezzo, Italy

Died: March 1, 1697 in Pisa Italy, buried in Arezzo

Nationality: Italian (Tuscan)

Educatio n: University of Pisa in Italy

Published Works: Francesco Redi on Vipers ( Osservazioni intorno alle vipere), Experiments on the Generation of Insects ( Esperienze Intorno alla Generazione degli Insetti), Bacchus in Tuscany ( Bacco in Toscana)

Redi's Major Scientific Contributions
Experimental Toxicology
Redi studied venomous snakes to dispel popular myths about them. He demonstrated that it is not true that vipers drink wine, that swallowing snake venom is toxic, or that venom is made in a snake's gallbladder. He found that venom was not poisonous unless it entered the bloodstream and that the progression of venom in the patient could be slowed if a ligature was applied.

His work paved the foundation for the science of toxicology.

Flies and Spontaneous Generation

One of Redi's most famous experiments investigated spontaneous generation. At the time, scientists believed in the Arisotelian idea of abiogenesis, in which living organisms arose from nonliving matter. People believed rotting meat spontaneously produced maggots over time.

However, Redi read a book by William Harvey on generation in which Harvey speculated insects, worms, and frogs might arise from eggs or seeds too tiny to be seen. Redi devised and performed an experiment in which he divided six jars into two groups of three. In each group, the first jar contained an unknown object, the second jar contained dead fish, and the third jar contained raw veal. The jars in the first group were covered with fine gauze that permitted air circulation, but kept out flies. The second group of jars was left open. Meat rotted in both groups, but maggots only formed in the jars open to air.

He performed other experiments with maggots. In another experiment, he placed dead flies or maggots in sealed jars with meat and observed living maggots did not appear. If living flies were placed in a jar with meat, maggots did appear. Redi concluded maggots came from living flies, not from rotting meat or from dead maggots.

The experiments with maggots and flies were important not only because they refuted spontaneous generation, but also because they used control groups, applying the scientific method to test a hypothesis.

Redi was a contemporary of Galileo, who faced opposition from the Church.

Although Redi's experiments ran contrary to the beliefs of the time, he did not have the same sort of problems. This may well have been because of the different personalities of the two scientists. While both were outspoken, Redi did not contradict the Church. For example, in reference to his work on spontaneous generation, Redi concluded omne vivum ex vivo ("All life comes from life").

It's interesting to note that despite his experiments, Redi believed spontaneous generation could occur, for instance, with intestinal worms and gall flies.
Parasitology
Redi described and drew illustrations of over one hundred parasites, including ticks, nasal flies, and the sheep liver fluke. He drew a distinction between the earthworm and the roundworm, which were both considered to be helminths prior to his study.

Francesco Redi performed chemotherapy experiments in parasitology, which were noteworthy because he used an experimental control. In 1837, Italian zoologist Filippo de Filippi named the larval stage of the parasitic fluke "redia" in honor of Redi.
Poetry
Redi's poem "Bacchus in Tuscany" was published after his death. It is considered among the best literary works of the 17th century. Redi taught the Tuscan language, supported the writing of a Tuscan dictionary, was a member of literary societies, and published other works.
Recommended Reading
Altieri Biagi; Maria Luisa (1968). Lingua e cultura di Francesco Redi, medico. Florence: L. S. Olschki.

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Francesco Redi - Spontaneous Generation, Parasites, and More

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Francesco Redi was an Italian naturalist, physician, and poet. Besides Galileo, he was one of the most important scientists who challenged Aristotle's traditional study of science. Redi gained fame for his controlled experiments. One set of experiments refuted the popular notion of spontaneous generation -- a belief that living organisms could arise from nonliving matter.

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1670: Anton Van Leeuwenhoek creates the first single lens microscope. (The Editors of Encyclopedia Britannica, 2018)

This new invention was substantial to the discovery of cells, functioning similar to a magnifying glass.

The single lens greatly amplified the view of miniscule specimens. (Such as cells.) (The Editors of Encylopedia Britannica, 2018)

1674: His creation of this new microscope leads him to discover red blood cells. (Davis, 2022)

Due to his invention, Leeuwenhoek was the first to measure the size of these cells accurately. (Davis, 2022)

He also was able to examine some of the first single-celled forms. (Protists.)

His discovery helped develop the 2nd tenet of cell theory, stating that cells are the basic unit of structure and function in all organisms. He contributed to this tenet by observing the first living cells. His invention of the light microscope and his idea of using photons to observe specimens on a smaller scale caused more developements in cell theory to be made in the future.