A: Anthrax is mainly a disease of grazing animals. The rod-shaped bacteria, called Bacillus anthracis, spend most of their time as spores in the soil, encased in a tough shell and practically lifeless. But when an animal swallows or inhales these spores, they come to life, and exude a protein which allows them to burrow into the white blood cells called macrophages.

Macrophages normally destroy bacteria. But safe inside one, anthrax bacilli shed their shells, multiply explosively, and swarm out into the bloodstream. There they keep dividing, producing toxins which cause the victim to go into toxic shock and die.

The dead animal is then attacked by scavengers, most of which can resist anthrax. It bleeds into the soil, and the hordes of bacilli in its blood turn back into spores, to await the next victim. They can survive for decades.

A: Spores on wool or hides usually cause a skin infection, nasty but treatable with antibiotics. Swallowing anthrax, in infected meat, produces a more serious intestinal disease which is frequently fatal. Inhaling the spores, as the victim in Florida did, is extremely rare, but nearly always fatal unless you take the right antibiotics before symptoms start.

The incubation period is anywhere from two days to two months. For respiratory anthrax, the earliest symptoms are flu-like - fever, headache, muscle pains. By the time coughing, painful breathing, and a tell-tale enlargement of the space under the breastbone permit a doctor to diagnose anthrax, it is too late for antibiotics. Those will kill the bacteria, but the toxins already produced will still kill the victim.

A: Anthrax spores are tough, fairly easy to culture and have a long shelf-life: spores seized from a World War One German spy targeting allied pack animals in Norway were revived after 80 years. They also survive delivery via bombs, shells or sprays better than many other pathogens.

A human with anthrax cannot infect someone else, which could be seen as useful on a battlefield. Spores released in a fine, inhalable mist - the main difficulty with mass administration of anthrax - should affect only the target troops, rather than creating a general epidemic.

This might limit the appeal of anthrax as a doomsday, terrorist bug - although being unable to diagnose it until it is too late for treatment does give anthrax a particular horror. It is easy to handle and obtain - animal anthrax occurs almost worldwide.

A: Anthrax figured in every known bio-arsenal of the last century, including those of Britain, the US, Japan, the Soviet Union and Iraq. But no one ever used them in battle, although Japan did tests on humans. Britain infected a Scottish island, Gruinard, while testing anthrax weapons, and only succeeded in cleaning it up with massive formalin treatments decades later.

No successful terrorist use of anthrax is known, unless that was the intent in the US and Kenya - in which case, it was the first to work. The murderous Aum Shinrikyo cult in Japan tried spraying anthrax, but used only a harmless, vaccine strain, either by mistake, or to practice. Foul play has long been suspected, but never proved, in an economically devastating outbreak of anthrax in Zimbabwe in 1979 which helped tip the political balance.

The Soviet Union had anthrax missiles, shells and cluster bombs, antibiotic and vaccine resistant strains, highly infectious strains, and recipes for reliable aerosols. Like every other admitted bioweapons state in the world, it is now meant to have destroyed its stocks.

A: Anthrax researchers, and many members of the US, Canadian and British military, have had an anthrax vaccine based on the first toxin the bacteria produces during infection. However, this is decades old, might cause side-effects, and is of unknown worth against inhaled anthrax. And there isn't much available. The US had to curtail plans to vaccinate all its troops due to production problems, while a similar British vaccine is also in short supply. Vaccines based on live bacteria bereft of some toxin genes are recommended only for animals in the West, although Russians have used live vaccines.

Scientific research is underway in many countries, especially the US, to improve anthrax vaccines and treatment, and to diagnose infection before it is too late to treat. Researchers are also learning which genetic variants of anthrax live where, so as to pin down the source of any attack. Such methods showed that the anthrax used in Florida is related to common North American varieties.

The best hope might be a more vigorous enforcement of the 1972 international treaty banning biological weapons. But an agreement on the mechanisms for monitoring compliance was blocked by the US this year.