Tissue Culture

In 1907 American biologist Ross Granville Harrison stumbled upon the amazing discovery that living tissues could be cultured, or grown, outside the body. Although Harrison could not have known it at the time, his discovery would become one of the most valued techniques in medicine. Tissue culture has opened up new ways to study the development of genes (the basic units of heredity), embryos, tumors, toxins, and the pathogens that cause numerous diseases. The technique is also used to produce medicines, vaccines, and replacement tissues, as well as to clone animals, such as Dolly, the famous sheep.
In late summer of 1906 Harrison, an expert on embryos, wanted to solve what was then an important problem in biology. Harrison set out to determine whether nerve fibers grow in local tissues of the body or originate in nerve cells of the brain. He had to devise a new way to study the problem because all the available living specimens contained both nerves and surrounding tissue.
Harrison decided to study living nerves in the absence of any surrounding tissue. To do this, he isolated a portion of the hindbrain of a tiny living frog embryo. To keep his specimen alive, he immersed it in fresh frog lymph (a diluted blood plasma carried by the lymphatic system) and placed it under a cover slip so he could examine it with a microscope. The frog lymph quickly clotted, like blood, and he sealed it with wax to prevent evaporation or contamination of the specimen.
Using a microscope, Harrison discovered that the nerve fiber did actually come from the brain, not the surrounding tissue. Harrison noticed something else: The frog's brain cells were still growing, even though they were no longer in the frog's body. Harrison found the answer to the question he was asking and, at the same time, invented what would become the science of tissue culture. Harrison reported his result in May 1907. Since then tissue culture has allowed researchers to learn more about the basic mechanisms of disease than had been learned in the previous 500 years.
source: encarta encyclopedia