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can stay suspended for hours, ready to be sucked into another person's lung. A larger particle would get caught in the mucus that lines the airways to trap such invaders. But these tiny droplets slip through into the tiny mucus-free air sacs that make up the sponge-like lung. Although the bacilli have evaded the mucus, the body does have another trap waiting. In the air sacs, cells known as macrophages (from the Greek words for "big eater") lie in wait to eat such foreign invaders. Unfortunately, unlike most bugs, TB bacilli are very comfortable in the belly of the macrophages. The chemicals inside the macrophage that kill most germs do not harm Mycobacterium tuberculosis. If they were properly armed by the immune system, the macrophages could kill TB, but it takes the immune system, three weeks to notice a tuberculosis infection. Meanwhile tuberculosis reproduces happily inside the "big eaters".
When finally armed, macrophages can kill the bacilli, but they often die themselves in the process, release their chemicals in the lung, and kill lung cells. A cheesy mass of dead cells forms in the midst of the healthy pink spongy lung. And sometimes a few bacilli survive even the armed macrophages. These lie waiting for a moment of weakness wehn they can begin to reproduce again. When their host is severely overworked or underfed or very sick or takes up smoking, they start to proliferate. The host's body resents the sudden growing presence of hundreds of tiny bacilli and orders the immune system to destroy them, but, in the process, it destroys nearby lung cells as well. Eventually blood vessels in the tattered lungs wear through and the host coughs bright red blood. Death can follow. Sometimes such a large vessel is damaged that the patient bleeds to death, or the soup of bacilli and dead lung cells can spill into the bloodstream, causing deadly toxic reaction. Or sometimes the lung is so eroded it collapses upon itself like a popped balloon.
While tuberculosis most often infects the lungs, the germ has many hiding places in the body. The lungs are a favored spot because of the ease with which the germ can travel on the air into the lungs, and the steady supply of oxygen that it receives there, but tuberculosis has alos been known to travel into the body in contaminated, unpasteurized milk and set up shop in the intestines. Sometimes tuberculosis hides in the lymph nodes of the neck and swells the throat like a horrible case of mumps; at other times it hides in the voice box and steals the voice. It an infect the kidneys, the skin, the blood, or the lining of the brain.
Tuberculosis can also infect the bones, and it is in the bones that we can read its history. The lungs and throats of the dead decay with time and leave no discernible trace, but bones riddled with characteristic cavities whre they have been eroded by TB have remained for thousands of years as proof of infection. In 1907, in Heidelberg, Germany, archaeologists found the six-thousand-year old spine of a young man whose fourth and fifth thoracic vertebrae, which are high up in the back, were eaten away. His spine had collapsed forward under the weight of his head, giving him the sharp-angled hump that is the telltale sign of tuberculosis of the spine. In addition to the bones, over the centuries artists have left us images of these high, pointy hunchbacks. Images or bones found in Egypt, China, Peru, California, and Tennessee tell us that tuberculosis, unlike smallpox, had traveled around the world and to the Americas long before Columbus. If there had been any doubt, in 1994 scientists found tuberculosis DNA, the chemical fingerprint of the germ, in a nine-hundred-year-old Peruvian mummy.