The discovery and introduction of the term "cell" belongs to R. Hooke. However, the scientist perceived it (the cell) as a void in the homogeneous (homogeneous) substance that made up the plant. The animal cell was first described by Levenguk, who discovered red blood cells and sperm. Instruments (microscopes) used by researchers of the 17-18 centuries did not allow to reliably establish any common microscopic structure of the elements of animal organs.
Despite the fact that plant components were more accessible for study, the cellular theory was a fragmented and unsystematic knowledge. After Hooke, researchers say that plant tissues have a specific structure, characterized by the presence in different parts of different microscopic elements. But no conclusions or generalizations from the observations were made then.
In the 18th century, microscopic studies did not provide any qualitatively new knowledge. Only with the start of factory production of microscopes did the study continue. By the 30s of the 19th century, the work of leading botanists of that time made it possible to strengthen knowledge of the elementary structure of plants. From that moment, the cell receives the status of "elementary structure". Using the method of maceration (infusion), the assumption about the presence of common walls of microscopic particles is destroyed. Thus, scientists come to the conclusion that the cell is a closed structure. Moreover, it is endowed with some independence.
G. Moth and L. Kh. Treviranus reveal that plant structures in which no cell structure is found are formed initially by the fusion of individual cells. The elementary system acquires the significance of a morphological and physiological component in which an independent metabolism occurs.
The microscopic anatomy of an animal organism has been actively studied by the Mueller School and the Purkinje School. Thanks to their work, a huge amount of factual material was collected.
The directly formulated cellular theory of the structure of organisms was Schwann (German zoologist, researcher) in 1839. Due to the fact that in his research the zoologist was based on the works of the botanist Schleiden, the latter is rightfully considered to be a co-author of Schwann.
The cell theory was a generalization of numerous data, based on the similarity of animals and elementary plant structures. The same mechanism of their formation was proved. Thus, Schwann's cellular theory characterizes the cell as the functional and structural basis of a living being.
Subsequently, researcher M. Badi applied this knowledge to the study of protozoa. K. Siebold finally formulated (in 1845) the provision on the unicellular nature of protozoa.
Cell theory was, however, revised at the end of the 19th century. R. Virchow (German scientist) put forward a new assumption. Based on new data, he concluded that a cell is formed only from a preexisting cell. Virchow also put forward the hypothesis of a "cell state." According to this assumption, a multicellular organism includes relatively independent units, the vital activity of which is carried out in close interconnection with each other.
Cellular theory has become a reflection of morphological unity in all organic nature. This, in turn, contributed to the development and strengthening of evolutionary doctrine.
Modern cellular theory is based on three points.
According to the first thesis, the elementary structure correlates with the wildlife of the whole planet. In other words, this statement states that, regardless of life form, structural, genetic and functional development is provided only by the cell.
According to the second provision, the emergence of new elementary units occurs only on the basis of the division of preexisting. At the same time, all cells equally preserve biological information, apply information to perform their tasks on the basis of protein synthesis.
According to the third statement, the elementary structure is correlated with a multicellular organism, which is characterized by systemic organization and integrity.