inThuringia, Germany, dedicated to the manufacture of high-quality
scientific instruments. Zeiss’s microscopes, employing Lister’s ideas,
were the finest in the world but not widely distributed. With their
cutting-edge instruments, German universities began to attract the
greatest minds in the fields of botany and biology.
Several of the best young scientists were students of a professor at
Berlin University named Johannes Peter Müller. Accomplished in the
study of physiology—how living organisms function—Müller pro-
moted the use of the microscope and chemical analysis in research. He
also urged his students to combine the quest for facts with philosophi-
cal thinking—to think beyond the accepted
truths of the time. In 1837 two of Müller’s
students, Matthias Schleiden and Theodor
Schwann, were dining out in Berlin when
their discussion turned to a recent discovery
about plant cells. Schleiden, a botanist him-
self, noted that the Scottish botanist Robert
Brown had found that various types of plant
cells all had nuclei.This got Schwann, an animal physiologist, to think-
ing about similar structures in animal tissues. The next day Schwann
and Schleiden examined a rod-shaped tissue called a notochord—the
embryonic spinal cord in vertebrates—under the microscope. Indeed
they saw that the cells of the notochord contained nuclei. Schleiden
was inspired to examine a variety of plant tissues with the microscope,
sketching the cells and nuclei of an orchid, a palm, and a cherry rice-
flower. He affirmed in an article that cells and their nuclei are the fun-
damental building blocks of plants. Schwann found the same kind of
structures in various animal tissues, from the pith of bird feathers to
the aorta of a pig fetus. He suggested that all animal tissues are made
of cells. More important, Schwann proposed that the cell is the basic
unit of structure for all living organisms. He wrote in 1839, “It may be
asserted that there is one universal principle of development for the
elementary parts of organisms, however different, and that this prin-
ciple is the formation of cells.”
8
Schwann called his proposition the
cell theory.
WORDS IN CONTEXT
physiology
The study of living
organisms and how
they function.
18
