This video segment from A Science Odyssey recounts the tactics employed by San Francisco's health officials to prevent bubonic plague from reaching America's West Coast. Using physical examinations, quarantines, and deportation, city officials hoped to isolate disease-carrying immigrants from the general population. They also disinfected people and fumigated properties where disease-carrying rodents were thought to exist. Following the 1906 earthquake, medical research began to consider rats, rather than humans, as the vector responsible for transmitting the disease. Scientists in India discovered that, in fact, it was the fleas carried by rats that were ultimately responsible for transmitting bubonic plague from diseased rats to humans.