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In 1879 Flemming found a new dye (a by-product of coal tar) that combined well with
particular, stringlike materials inside the cell nucleus and did not stain most other cell parts.
Finally, a dye existed that allowed him to focus his observations on one particular structure
within the cell’s nucleus.
He named the material stained by this dye chromatin (from the Greek word for color)
and began a series of experiments using salamander embryos. Flemming cut tissue-paper
thin slices of embryonic cells from fertilized salamander eggs and stained them with this
dye.
The dye, of course, killed the cells. This stopped all cell activity and cell division. But
it was a price Flemming had to pay in order to study these chromatin structures within the
cell nucleus. Since the cells were dead before he could observe them, what Flemming saw
through his microscope was a series of “still” images of cells frozen in various stages of division. Over time, and with enough samples to study, he was able to arrange these images in
order to show the steps of the cell division process.
As the process began, the chromatin collected into short, threadlike objects (whose
name Flemming changed from chromatin to chromosomes from the Greek words meaning
“colored bodies”). It was soon clear to Flemming that these threadlike chromosomes were a
key feature of cell division. Therefore, Flemming named the process mitosis, from the
Greek word for thread. The words chromosomes and mitosis are still used today.
Flemming saw that the next step was for each individual chromosome thread to break
into two identical threads, doubling the number of chromosomes. These two identical sets
of chromosomes then pulled apart, half going to one end of the cell, half going to the other.
The cell itself then divided. Each of the two offspring cells was thus stocked with a complete set of chromosomes that was identical to the original parent.
Flemming had discovered the process of cell division and published his results in
1882. The real value of Flemming’s discovery lay hidden for 18 years. Then, in 1900, Hugo
deVries put Flemming’s discovery together with Gregor Mendel’s discoveries on heredity
and realized that Flemming had discovered how hereditary traits were passed from parent to
child and from cell to cell.
Fun Facts: Like all living species, humans grow from a single egg cell
into complex organisms with trillions of cells. Louise Brown, born July
25, 1978, in Oldham, England, was the first human test-tube baby. Her
first cell divisions took place not in her mother’s womb, but in a laboratory test tube.
More to Explore
Adler, Robert. Medical Firsts. New York: John Wiley & Sons, 2004.
Alberts, Bruce. Molecular Biology of the Cell. Abingdon, England: Taylor & Francis,
1999.
Boorstin, Daniel. The Discoverers: A History of Man’s Search to Know His World and
Himself. New York: Random House, 1997.