Cytology, the clinical study of cells, was born in 1665 when Robert Hooke observed the empty cell walls of cork and created the word cellulae (” little cells”) to explain them. Soon he studied thin pieces of fresh wood and saw living cells “filled with juices”– a fluid later on called protoplasm. 2 centuries later on. Theodor Schwann studied a large range of animal tissues and concluded that animals are made from cells.
Schwann and other biologists initially thought that cells originated from nonliving body fluid that in some way hardened and obtained a membrane and nucleus This concept of spontaneous generation– that living things emerge from nonliving matter– was rooted in the clinical idea of the times. For centuries, it appeared to be basic good sense that decomposing meat became maggots, kept grain into rodents, and mud into frogs. Schwann and his contemporaries simply extended this concept to cells The concept of spontaneous generation wasn’t challenged till some timeless experiments by French microbiologist Louis Pasteur in1859 By the end of the 19th century, it was developed beyond all affordable doubt that cells emerge just from other cells.
The development of biochemistry from the late nineteenth to the twentieth century made it even more obvious that physiological processes of the body are based upon cellular activity which the cells of all types display amazing biochemical unity. Therefore emerged the generalizations that make up the contemporary cell theory:
1. All organisms are made up of cells and cell products.
2. The cell is the most basic structural and practical unit of life. There are no smaller sized subdivisions of a cell or organism that, in themselves, live. An enzyme molecule, for instance, is not alive, although the life of a cell depends upon the activity of many enzymes.
3. An organism’s structure and all of its functions are eventually due to the activities of its cells.
4. Cells come just from preexisting cells, not from nonliving matter. All life, for that reason, traces its origins to the very same initial cells.
5. Due to the fact that of this typical origins, the cells of all types have numerous essential resemblances in their chemical structure and metabolic mechanisms.