Cancer is a mysterious group of diseases which often arouses fearful images of death. There are over one hundred different types of cancer, which can be distinguished by the type of cell or organ which is affected, the treatment plan employed, and the cause of the cancer. Any substance or agent that can cause cancer is called a carcinogen. One of the first people to suspect that certain substances in the environment can cause cancer was Sir Percivall Pott (1714-1788), who in 1775 published a paper on cancer occurrence in chimney sweeps. It has since been discovered that benzo(a)pyrene, a chemical found in soot, is a potent carcinogen. Ionizing radiation was first suspected of being carcinogenic around the turn of the twentieth century, when physicians who developed the use of X-rays and radium in medicine showed a high incidence of skin cancer. Later, in 1915, scientists in Japan...