Keywords

Chromosomes, globules

Abstract

The cellular theory was produced in two steps by Schleiden and Schwann (1838–1839) and then by Remak (1855) and Wirchow (1855–1858). This theory claimed that cells were universal and microscopic entities, constituting living beings and that a cell was always produced by the division of another cell. Since that period up to now, the cell has become a central concept in biology.

History

The cellular theory was formulated after more than one and a half century of microscopic observations. Indeed, the invention of microscope during the seventeenth century offered new investigations to naturalists. Robert Hooke (1635–1703) in his Micrographia (1865), Antoni van Leeuwenhoek (1632–1723), Jan Swammerdam (1737–1780)… observed microscopical objects: individual entities, often named animalcules, and parts of organisms. However, they did not have concepts to consider all these new observations. For example, it is important to notice that when Hooke used the word cell to name some little spaces that he had observed in vegetable organism he did not expect to conceptualize anything, his intention was only descriptive.

During all the eighteenth century, microscopic observations were more and more accurate. They showed a broad diversity of animalcules and microscopic structures in living beings. At the beginning of the nineteenth century, some theories claimed that there could be a unity in the microscopic structure. The French botanist Charles-François Brisseau de Mirbel (1776–1854) suggested that plants were constituted by a set of membranes with a lot of pores. A few years later, René Joachim Henri Dutrochet (1776–1847), who had discovered the osmotic phenomenon, claimed that cells constituted plants. However, in the wall of these cells there could be some little globules that could be the fundamental entities. Then, François-Vincent Raspail (1794–1878) (the inventor of the microscopic colorations) considered that living beings were made of globules that were to be formed in the wall of other globules which would fit into each other.

In the period? Lorenz Okenfuss (Oken) (1779–1851) claimed that living beings were a synthesis of infusorians. All these proposals have in common the fact that they are conceptions about the possibility of a microscopic and universal structure.

In 1838, the German botanist Matthias Schleiden (1804–1881 claimed that vegetable organisms were composed of cells in which there was a systematic structure, the cytoblast (that will be later named nucleus). Besides, Schleiden suggested that cells were the result of the accumulation of a liquid, the cytoblastem, between the cytoblast and the membrane. His colleague, Theodor Schwann (1810–1882), a specialist of animal physiology, generalized this theory to animals and indicated that the cytoblastem came from the interstitial fluid.

During the 1850s, Robert Remak (1815–1865) and Rudolph Virchow (1821–1902) independently (Remak in 1855 and Virchow in 1855–1858) asserted that every cell was the result of the division of a previous cell. From this time forth, the concept of cell has become central in biology.

During the end of the nineteenth century, the progress of microscopy led to observations of chromosomes and to the description of mitosis (Fleming 1882) and meiosis (Boveri, Hertwig 1887–1892).

See also

Cell

Protoplasmic Theory of Life

Spontaneous Generation (History of)