1900: The era of scientific medicine is only just beginning. If you become sick or injured, you'll need a strong constitution, or plenty of luck, to survive. It's been a few decades since the French scientist Louis Pasteur discovered the microscopic creatures we call "bacteria" and demonstrated that these "germs" could cause many illnesses. But despite these discoveries, many people continue to blame sickness on a variety of human traits and social conditions -- a poor constitution, a "degenerate" lifestyle, or miasmic clouds of filth emanating from city slums. Though the scientific community knows that germs cause disease, they don't completely understand how they're spread, and they certainly don't know how to destroy them.

Here are a few steps on the science odyssey from then to now, including links to activities and databank entries on this site.

• In 1900, the bubonic plague hits San Francisco. Armed with an understanding that germs cause disease, Chinatown is quarantined to prevent spread of the plague. Doctors have few of the tools we are now accustomed to for the treatment of such diseases.
  

  You Try It: Doctor over Time
  Discoveries: Bubonic plague hits San Francisco
  

• In 1909, Paul Ehrlich develops the first drug that can cure a specific illness by killing the germ that has invaded the body.
  

  Discoveries: Ehrlich finds cure for syphilis

• In 1915, Joseph Goldberger identifies another potential cause of disease, poor diet.
  

  Discoveries: Pellagra shown to be dietary disease
  People: Joseph Goldberger

• In 1918, a deadly worldwide outbreak of the flu points out the limits of the powers of medicine, as well as the destructive side effects of war.
  

  Discoveries: Worldwide flu pandemic strikes

• In 1922, researchers find a way to treat diabetes, until then untreatable.
  

  Discoveries: Banting and Best isolate insulin
  People: Frederick Banting
  People: Charles Best

• In 1928, a potent substance that can kill bacteria is isolated in the laboratory, but it will be nearly twenty years before it is used to combat infection and disease.
  

  Discoveries: Fleming discovers penicillin
  People: Alexander Fleming
  People: Ernst Chain
  People: Dorothy Hodgkin

• In the next two decades, many more pharmaceuticals appear on the market to treat a range of diseases, including infections, glaucoma, and arthritis.
  

  You Try It: Doctor over Time
  People: Percy Julian
  

• In the 1950s, new vaccines become available that prevent dreaded childhood diseases, including polio.
  

  On the Edge: Paralyzing Polio
  Discoveries: Salk produces polio vaccine
  People: Jonas Salk
  

• Researchers during that decade and beyond study various biochemicals, gradually developing pharmaceuticals that can combat certain forms of cancer.
  

  Discoveries: Drugs developed for leukemia

• Offshoots of that same work led to the development of drugs that affected the immune system, allowing the first successful organ transplants.
  

  Discoveries: First successful kidney transplant performed
  People: Christiaan Barnard

• By the end of the 1970s, optimism about modern medicine is running high, as more and more diseases appear to be conquered.
  

  Discoveries: World Health Organization declares smallpox eradicated
  People: Donald Hopkins

• But in 1981, the accomplishments of medicine are challenged as a new deadly disease, AIDS, is identified. It will be several years before viable treatment methods for AIDS are available.
  

  On the Edge: Hip Hop with Dr. Ho
  Event: AIDS is officially recognized
  

Today: Life expectancy has risen dramatically, but poverty and the environment are still major factors affecting health worldwide. The average citizen knows a great deal about how to maintain health. Antibiotics have proven an indispensable tool in battling illness, but resistant strains of bacteria demand newer and stronger drugs. Organ transplants and high-tech medicine give thousands of people each year a second chance at life, but the medical system has become big business, and there is heated debate over access and cost of care. New disease organisms challenge the limits of scientific medicine.