Diseases are any harmful change that interferes with the normal appearance, structure, or function of the body or any of its parts. Since time immemorial, disease has played a role in the history of societies. It has affected and has been affected by economic conditions, wars, and natural disasters. An epidemic of influenza that swept the globe in 1918 killed between 20 million and 40 million people. Within a few months, more than 500,000 Americans died^more than were killed during World War I 1914-1918, World War II 1939-1945, the Korean War 1950-1953, and the Vietnam War 1959-1975 combined. Diseases have...
life span of about 50 years. By the time the century neared its close, average life span had risen to 76 years. Other developed countries experienced similar increases. Much of the credit for these longer life spans, and for the good health that accompanies them, is due to the conquering of diseases, thanks to vaccines, antibiotics, sophisticated surgical tools, and other medical miracles. The challenges ahead include bringing the benefits of this medical knowledge to all peoples of the world, and expanding on current knowledge in order to understand, treat, and prevent the diseases that still confront us.