The big health crisis today is AIDS, but a century ago the scourge was yellow fever, a disease that was just as terrifying to Americans.

In 1888, Jacksonville, Fla., witnessed the most serious epidemic in its history, a yellow fever crisis that took 427 lives. Public health services in Florida's largest city would never be the same.

To be sure, yellow fever epidemics were not new to Americans in the late 1800s. The disease wiped out 700 residents of Philadelphia, one sixth of the population, in 1699, and epidemics raged in Charleston, S.C., in 1702, 1741 and 1747. New York City experienced five different yellow fever epidemics in the century preceding the American Revolution. But none was worse than the Memphis outbreak of 1878, when about 16,000 perished; the population loss cost the city its corporate charter.

Jacksonville's epidemic was the last before the theory of Cuban physician Carlos Finlay was finally accepted by the medical profession in 1900. Finlay argued that the disease, characterized by high fever and jaundice (hence the "yellow"), was not contagious, but spread by a mosquito bite.

The Jacksonville epidemic of 1888 was preceded by a few isolated cases in the spring. Then, on July 28, a Tampa man who traveled to Jacksonville came down with the disease, and within a few days the Jacksonville board of health declared that yellow fever was reaching epidemic proportions. The next stage was sheer panic: Jacksonville residents fled the city, overloading trains and boats in a desperate attempt to avoid the disease.

No community in Florida or Georgia wanted to accept the Jacksonville emigrants, or even permit them to travel through their environs. Waycross, Ga., officials threatened to destroy railroad tracks if Jacksonville's residents attempted to come through town, even in enclosed rail cars, and St. Augustine postal authorities returned all mail from Jacksonville even though officials claimed that they had fumigated each piece using dry heat.

Federal authorities were pressured to intervene by Florida and Georgia leaders because the Sunshine State had no state board of health to deal with the emergency. So the United States Marine Hospital Service set up several refugee camps outside the city, requiring every emigrant from Jacksonville to spend a minimum of 10 days in quarantine. But the outdoor, tent-city conditions of the centers were worse than the risk of getting yellow fever by staying in Jacksonville.

Many Americans were moved by Jacksonville's tragedy, sending $345,000 in contributions and supplies. The Jacksonville Auxiliary Sanitary Association, composed of public-spirited citizens, worked tirelessly to make certain that donations were turned into adequate supplies for the city's needy. For four months, the association provided each adult in need a weekly ration of two pounds of bacon, three pounds each of meal and grits, a pint of molasses, a half pound of sugar and a bar of soap.

Business in the city came to a standstill. Streets were fumigated daily with a solution of bichloride of mercury, a powerful antiseptic; trash was burned; infected houses were marked by yellow flags, and citizens were urged to stay in their houses from sunset to sunrise, which was thought to be the most likely time for contracting the disease.

No one knew how the disease was spread, but efforts to cope with the epidemic were based on the mistaken assumption that it was contagious. One approach, dubbed the concussion theory, mandated firing cannons into the air to dispel yellow fever microbes; the only effect was the damaging of certain buildings. Every piece of mail leaving Jacksonville between Aug. 1 and Dec. 1, 1888, went through a four-stage disinfectant process, more than 2 1/2 million letters in all.

Only cold weather, beginning with a hard freeze on Nov. 26, brought the epidemic to an end. The last death occurred on Dec. 5, and refugees were permitted to return to the city 10 days later. But the toll was enormous: 4,704 cases, with almost a 10 percent mortality rate. Jacksonville's tourist business, hurt in the previous few years by unseasonably cold weather, would not begin to recover until 1890.

Nevertheless, there was a silver lining in the dark yellow cloud. Jacksonville citizens used unspent contributions ($24,750) to help Johnstown, Pa., residents after a major flood in 1889, and Russians experiencing famine in 1892. The yellow fever crisis moved the Florida legislature in 1889 to do what it had been authorized by the state constitution of 1885 -- establish a state board of health.

Cuban physician Carlos Finlay turned out to be right, but public skepticism remained even after his theory was accepted by the medical profession in 1900. No voice was more scathing than that reflected in newspaper editorials. "Of all the silly and nonsensical rigamarole about yellow fever that has yet found its way into print," declared one screed dated Nov. 2, 1900, ". . . the silliest beyond compare is to be found in the mosquito hypothesis." That editorial, incidentally, appeared in The Washington Post.

Thomas V. DiBacco is a historian at The American University.