Transcript 1590 Two Dutch eye glass makers, Zaccharias

1590
Two Dutch eye glass makers, Zaccharias Janssen
and son Hans Janssen experimented with two lenses
placed in a tube. The Janssens observed that viewed
objects in front of the tube appeared greatly enlarged,
creating both the forerunner of the compound
microscope and the telescope.
Zacharias Janssen
In 1665, the English physicist Robert
Hooke looked at a sliver of cork through
a microscope lens and noticed some
"pores" or "cells" in it. Robert Hooke
believed the cells had served as
containers for the "noble juices" or
"fibrous threads" of the once-living cork
tree. He thought these cells existed only
in plants, since he and his scientific
contemporaries had observed the
structures only in plant material.
Robert Hooke wrote Micrographia, the
first book describing observations made
through a microscope. The drawing to
the top left was created by Hooke.
Hooke was the first person to use the
word "cell" to identify microscopic
structures when he was describing cork.
The father of microscopy, Anton Van Leeuwenhoek of Holland (1632-1723),
started as an apprentice in a dry goods store where magnifying glasses were
used to count the threads in cloth. Anton van Leeuwenhoek was inspired by
the glasses used by drapers to inspect the quality of cloth. He taught himself
new methods for grinding and polishing tiny lenses of great curvature which
gave magnifications up to 270x diameters, the finest known at that time.
These lenses led to the building of Anton Van
Leeuwenhoek's microscopes considered the first practical microscopes, and
the biological discoveries for which he is famous. Anton Van Leeuwenhoek
was the first to see and describe bacteria (1674), yeast plants, the teeming life
in a drop of water, and the circulation of blood corpuscles in capillaries. During
a long life he used his lenses to make pioneer studies on an extraordinary
variety of things, both living and non-living, and called these structures
“animalcules”.
Mathias Jacob Schleiden, German botanist.
Schleiden was educated at Heidelberg (1824–
27) and practiced law in Hamburg but soon
developed his hobby of botany into a full-time
pursuit. Repelled by contemporary botanists’
emphasis on classification, Schleiden preferred
to study plant structure under the microscope.
While professor of botany at the University of
Jena, he wrote “Contributions to Phytogenesis”
(1838), in which he stated that the different
parts of the plant organism are composed of
cells or derivatives of cells. Thus, Schleiden
became the first to say that plants were made
of cells. He also recognized the importance of
the cell nucleus. He became professor of
botany at Dorpat, Russia, in 1863.
1839
Theodor Schwann (1810–1882), a
German, proposed that in animals
too every structural element is
composed of cells or cell products.
Schwann's contribution might be
regarded as the more
groundbreaking, since the
understanding of animal structure
lagged behind that of plants. In
addition, Schwann made the
explicit claim that the fundamental
laws governing cells were identical
between plants and animals: "A
common principle underlies the
development of all the individual
elementary subunits of all
organisms."
1855
Virchow was a German physician who studied cells. He stated that
living cells come only from other living cells (This is a part of cell
theory.) Virchow’s greatest accomplishment was his observation
that a whole organism does not get sick—only certain cells or
groups of cells. In 1855, at the age of 34, he published his now
famous aphorism “omnis cellula e cellula” (“every cell stems from
another cell”).