Microbiology, 2021

78 3 • The Cell
discoveries leading to a better understanding of what we now call the cell theory. Modern cell theory has two
basic tenets:
• All cells only come from other cells (the principle of biogenesis).
• Cells are the fundamental units of organisms.
Today, these tenets are fundamental to our understanding of life on earth. However, modern cell theory grew
out of the collective work of many scientists.
The Origins of Cell Theory
The English scientist Robert Hooke first used the term “cells” in 1665 to describe the small chambers within
cork that he observed under a microscope of his own design. To Hooke, thin sections of cork resembled
“Honey-comb,” or “small Boxes or Bladders of Air.” He noted that each “Cavern, Bubble, or Cell” was distinct
from the others (Figure 3.5). At the time, Hooke was not aware that the cork cells were long dead and,
therefore, lacked the internal structures found within living cells.
Figure 3.5
Robert Hooke (1635–1703) was the first to describe cells based upon his microscopic observations of cork. This illustration
was published in his work Micrographia.
Despite Hooke’s early description of cells, their significance as the fundamental unit of life was not yet
recognized. Nearly 200 years later, in 1838, Matthias Schleiden (1804–1881), a German botanist who made
extensive microscopic observations of plant tissues, described them as being composed of cells. Visualizing
plant cells was relatively easy because plant cells are clearly separated by their thick cell walls. Schleiden
believed that cells formed through crystallization, rather than cell division.
Theodor Schwann (1810–1882), a noted German physiologist, made similar microscopic observations of
animal tissue. In 1839, after a conversation with Schleiden, Schwann realized that similarities existed between
plant and animal tissues. This laid the foundation for the idea that cells are the fundamental components of
plants and animals.
In the 1850s, two Polish scientists living in Germany pushed this idea further, culminating in what we
recognize today as the modern cell theory. In 1852, Robert Remak (1815–1865), a prominent neurologist and
embryologist, published convincing evidence that cells are derived from other cells as a result of cell division.
However, this idea was questioned by many in the scientific community. Three years later, Rudolf Virchow
(1821–1902), a well-respected pathologist, published an editorial essay entitled “Cellular Pathology,” which
popularized the concept of cell theory using the Latin phrase omnis cellula a cellula (“all cells arise from
cells”), which is essentially the second tenet of modern cell theory. 5 Given the similarity of Virchow’s work to
Remak’s, there is some controversy as to which scientist should receive credit for articulating cell theory. See
the following Eye on Ethics feature for more about this controversy.
5 M. Schultz. “Rudolph Virchow.” Emerging Infectious Diseases 14 no. 9 (2008):1480–1481.
Access for free at openstax.org.