HISTOLOGY
is, essentially, MICROANATOMY; that is, the
study of the structure (ANATOMY)
of small (MICRO) things. The
small things are the cells and their arrangement to constitute tissues
and, finally, the association among these to form organs.
Nowadays,
Histology also includes what is called Histophysiology; that is,
the study of the close associated function of cells / tissues.
So,
I believe that HISTOLOGY should be faced, literally, as HISTO + LOGOS ... meaning
the study of tissues, in both
a structural and functional perspective!
It is obvious
that the scientific knowledge about tissues was preceded by the study of
the respective units that constitute them. In 1665, Robert
Hooke (1635-1703), an English microscopist
and physic, when examining a piece of cork with a rudimentary microscope,
saw an abundance of empty small compartments — the “cell” was discovered!
Hooke derived the designation from the Latin, cellula
;
i.e., small compartment, having in mind a comparison with a honeycomb.
Indeed, we have a certain impression that he examined something empty —
that is why the designation is written in inverted commas. Therefore, the
designation of the units that constitute the living beings had a correct
etymological origin, but the concept was rather wrong. Almost two hundred
years were passed before a definition of cell was achieved; according to
Max
Schultze (1861): Cell
is a small mass of nucleated protoplasm. Nowadays,
we may say that Cell is the smaller quantity of protoplasm that possesses
a certain functional autonomy.
2. Then, how was achived the transition
from "empty cell” to the actual cell?
In that very year
Hooke
discovered the “cell”, he and Malpighi
were the first to observe the true units that form the tissues of animals,
but now the properly speaking cells. In this sequence, everything was in
standby for the discovery of the nucleus (from
the Latin, nucleus = almond). The first
description of the nucleus was carried out by Leeuwenhoek,
in 1700, when examining the red blood cells of the salmon. The first description
of the nuclear envelope was accomplished by Jan
Evangelista Purkinje (1787-1869), a Czech
biologist, in 1830; nevertheless, who verified the constancy of the organelle
and who introduced the term nucleus in microscopy was Robert
Brown (1773-1858), a Scottish botanist,
after the examination, in 1831, of epidermal cell of some orchids and some
Asclepiadacea. Purkinje
also introduced in Science the term protoplasma (1840).
3. Tell me. Are all the living beings
made of cells?
Almost all. In
fact, the cell is the fundamental unit that constitutes all the generality
of animals and plants. Protozoa and bacteria present only one cell; viruses
possess no cells. Wolff
(1759), Brisseau-Mirbel
(1802), Oken
(1805) and Lamarck
(1809) seemed to have recognized that the cellular organization is a characteristic
of all living beings they studied; however, Matthias
Schleiden (1804-1881), a German botanist,
in 1838, had the merit of having understanding the true importance of the
cells. He saw, under the microscope, thousands of plant specimens, and
inferred that all the vegetables are made of cells. By extension, similar
studies carried out on animals, in 1839, by Theodor
Schwann (1810-1882), a German zoologist
and physiologist, came to the conclusion that all the then known living
beings were composed of cells. Thus, the dogma called the cell
theory became established. According to it,
the living beings may grow and reproduce themselves because, in fact, the
cells may in turn multiply. In addition, it assumed that it is only possible
to form new cells from other pre-existing ones.
4. I was told
that someone was left behind in the authorship of the cell theory!
Unfortunately,
that seems to be so! Indeed, Rudolf
Virchow (1821-1902), a great German
pathologist, was not considered to be an author. Virchow gave a big contribution
to the establishment of the theory, when he demonstrated that the pathological
injuries also had a cellular structure; thus, he is considered to be the
pioneer of the cellular pathology. In the sequence of the works of Schwann,
Virchow
saw (1855/56) that all the cells of the pathological tissues derived from
healthy ones and that all living cells originated from pre-existing ones.
This discovery was known as the Law of Virchow
(or Fundamental Law of Biology).
Indeed, Virchow edified the bases of the modern Pathology, being the author
of the famous fundamental aphorism: Omnis
cellula e cellula ; that is, each cell
comes from another cell (1858).
5. OK! Then, tell
me when the tissues come into action!
Between the first
description of the nucleus and the statement of its constancy in the cell,
was introduced in Science the definition of tissue. The so-called 21 textures
of Marie François Bichat,
a French pathologist (1771-1802), are world famous. A texture was a “tissue”
(i.e., a body component) as perceived by its macroscopic physical properties.
We owe to him the notion of tissue, when he verified that certain textures
presented a thin thickness and were very flat, to the extent of being compared
to pieces of cloth. In ancient French, tissu
was the past participle of the verb tistre
or tître
that meant to weave (in modern French — tisser,
past participle tissé ).
Owing to the importance of his works, Bichat
is considered, by some authors, to be the founder of Animal Histology.
6. Only some authors?
Why not all?
Despite Bichat
is, virtually, the first histologist, Marcello
Malpighi (1628-1694), an Italian anatomist,
is in fact considered the true “Father of Histology”. Firstly, because
Malpighi
preceded Bichat
in a number of years; secondly, because Bichat never used a microscope,
indeed! — His textures were described based on dissections, carried out
with bistoury and scissors, and in the subsequent analyses of the macroscopic
physical characteristics of the different structures that form the human
organism. On the contrary, by using a microscope so rudimentary that could
be compared to a toy, Malpighi
described a series of microscopic structures never seen until then; for
instance, was the first scientist to observe the capillaries.
Although the modern
histologists only considered 4 fundamental kinds of tissues (i.e., epithelial,
connective, muscular and nervous), we must stress that taking into account
the subvarieties of each kind, we may state that the total number of tissues
actually described is not inferior to the above referred 21 textures of
Bichat.
Truthfully, these textures have anatomical and physiological reality; in
fact, the important contribution of Bichat‘s
works for the advance of Science forced Buckle
to assume that: "... between Aristotle
and Bichat I cannot find a man in between".
7. OK! Then, give
me now a definition of tissue?
Tissue is each
of the elementary multicellular components, microscopically and functionally
distinct, that constitute either animals or plants where they associate
to form organs and systems (Translated from M.
J. Xavier Morato.
Tecido Conjuntivo, Estrutura, Funções e Reacções.
Page 6. Lisboa, 1980).
8. I am still
waiting for the origin of the word HISTOLOGY!
17 years after
the death of Bichat,
that is to say, in 1819, A. Mayer
created the term Histology. In the sequence of the previous word tissu,
made use of two classical Greek root words (histos
= tissue and logos
= study). The term histos meant originally any woven material. In 1844,
it was recommended for large usage by Sir Richard
Owen (1804-1892), a great English palaeontologist.
9. Finally, who
wrote the first textbook of Histology?
It was Rudolph
von Kölliker (1817-1905), a Swiss
professor of Anatomy — Handbuch der Gewebelehre
(i.e., The book for teaching tissues), published in 1852; so, some authors
considered him the true founder of Histology.
