Cell Theory
Section 2.2. Due to improving of microscopic technique and as a result
from a number of studies carried out in the first half of the XIX
century, the concepts concerning the very essence and structure of cells
are also subjected to change. They are already accepted as structural
elements with a cell membrane, which can be linked to one another thus
forming tissues and organs. During this period the cell nucleus has been
discovered. This subject will be in detail treated in Chapter 3 (Section 3. 3).
The accumulation of a lot of experimental material in the studies on both
plant and animal cells gives rise to the idea of uniformity in the morphology of
the plant and animal kingdoms. Such an idea has been launched in a purely
contemplative manner by some philosophers and researchers at that time
while in 1838—1839 it has been finally shaped as a cell theory.
In literature the names of a number of authors have been indicated
as creators of the cell theory — C. F. Wolff, L. Oken, P. F. Goryaninov,
R. Dutrochet, J. E. Purkinje, G. Valentin, M. Schleiden, etc. It would only
be just a historical point of view to state that they all had a certain
tribute, especially Schleiden. The priority however for this great
discovery is due to the German physiologist and histologist Theodor
Schwann (1839) who has not only very clearly formulated the thought of
the uniformity in the building of plant and animal world, but has also
proved it with a convincing experimental material (Fig. 2–7).
The rise of the cell theory has met varying estimates. Some
investigators have accepted it as fully proven, while others were sceptical.
As a logical consequence from its basic premises the world of organisms
has been divided into two large groups: multicellular and unicellular. This
has on its part raised a number of questions: are protozoa cells or are they
organisms; what is a cell and what is an organism; are multicellular
organisms, their tissues and organs a mechanical sum of autonomous cells
or they display a specific wholeness; are there smaller units than the cells,
etc.
Some of these questions are quite reasonable and some of them have
already been answered in a satisfactory way, while others still remain
unanswered. Nevertheless, cell theory has passed the test of time and has
been acknowledged as the only right one in the explanation of living
organism structure.
Cell theory is one of the most fundamental generalizations in biology.
Very justly it is classified by F. Engels as one of the three remarkable
discoveries of the XIX century, together with the discovery of the law for the
preservation of energy and the role of the chemical evolution for the
creation of the living organisms.