FROM 1900 TO WORLD WAR II, great strides were made in understanding the structures, functions and chemistry of living organisms. Drugs to combat infectious diseases were developed, and x-rays were used to diagnose and treat illnesses. Cancer research in cell culture, chemical carcinogens, diagnostic techniques and chemotherapy firmly established oncology as an experimental science.

						Radiotherapy: Irradiation as Treatment Radium and x-rays were enlisted in the battle against cancer early in this century. Their first uses on humans were inconclusive, but tests on animals soon yielded the promising news that x-rays harmed rapidly multiplying cells more than others. Thus it was found that x-rays selectively damaged cancer cells, causing less harm to other tissues. As safe levels of dosage were determined, the therapy became standard.

		A Genetic Explanation for Cancer An early 20th-century theory that would reemerge as an important area of research later in the century held that cancer was due to abnormal chromosomes. Its leading advocate was professor of zoology at Wurzberg, Germany, Theodor Boveri.

		The First "Wonder-Drugs" Discoveries concerning infectious diseases and microbes late in the 19th century spurred the early 20th-century search for chemical weapons to fight illnesses. Through trial and error, the new science of chemotherapy produced natural and synthetic drugs to cure a number of diseases. While not effective against cancer, the new drugs encouraged researchers to continue the pursuit of chemical means to control cancer.

		Experiments in Search of Cancer's Causes Throughout the early decades of this century, researchers pursued different theories of the origin of cancer, subjecting their hypotheses to systematic experimentation. A viral cause of cancer in chickens was documented in 1911, and both chemical and physical carcinogens were conclusively identified. Chromosomal abnormalities were also investigated as possible causes of cancer.

		Bringing Cancer Into the Light of Day A need to combat rising public fear and ignorance concerning cancer led in 1913 to two significant events: publication of the first known article on cancer's warning signs in a popular woman's magazine, and formation of a nationwide organization dedicated to public education on cancer.

		New Ways to Test Theories: Advances in Experimental Techniques As investigations into the nature, causes and treatment of cancer, multiplied, new experimental techniques and laboratory methods came into use. In addition to the electron microscope and other new tools, specialized procedures such as growing cells in test tubes and breeding particular strains of mice soon became standard elements of research.

		Chemical Carcinogens The cancer-causing potential of chemicals had been suggested in the 18th century with Percivall Pott's observations on the high rate of cancer among chimney sweeps. Theory became fact in 1915 when experiments confirmed that cancer could be induced by chemicals.

		Sun and Radium: Tracking Physical Carcinogens Physical carcinogens were positively identified early in the 20th century. Some, such as the sun, had long been suspected as a cause of skin cancers. Others were more obscure and required investigative skills as well as laboratory tests.

		Cancer Statistics As experimental research on the nature and causes of cancer moved forward, the first reliable statistics on the incidence and mortality rates of cancer were compiled. This effort was undertaken in part to determine whether or not the disease was becoming more common, as it appeared to be.
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