Clay's Ark by Octavia E. Butler

put through.
    "What's the matter?" Meda asked softly. She had a big voice, not intended for speaking softly, but she managed. She
    had come closer. God help her, why didn't she go away? Why didn't he order her away or leave himself?
    She touched his arm. "Are you all right?"
    His body went on automatic. Helplessly, he grasped her hand. He managed not to scratch her, and tried to feel good
    about that until he saw that she had a small abrasion on the back of her hand. That was enough. His touch would
    probably have been enough anyway. Eventually she would have eaten something with that hand or scratched her lip or
    wiped her mouth or scratched or licked her hand to quiet the slight itching sensation contamination sometimes
    produced. And the disease organism could live on the skin for hours in spite of normal, haphazard hand-washing. Any
    person he touched was almost certainly doomed in one way or another.
    "Why are your hands wet?" she asked. And when he did not answer, she examined his hands. He had expected her to
    drop them in disgust, but she did not seem disgusted. She was a big, strong girl. Maybe she could be saved. Maybe he
    could save her -if he stayed.
    He remembered trying vainly to save his wife, Disa. She had been a short, slender woman with no weight to lose,
    barely big enough to qualify for the space program. The disease had eaten her alive. She had been one of the mission's
    two M.D.s, however, and before she died, she and Grove Kenyon, the other doctor, had discovered that the disease
    organism caused changes that could be beneficial-if the host survived its initial onslaught. Surviving hosts became
    utterly resistant to more conventional diseases and more efficient at performing certain specialized functions. Only the
    toxin excreted by the disease organism was life-threatening. Not surprisingly, the human body had no defense against
    it. But in time the organism changed, adapted, and chemically encouraged its host to adapt. Its by-products ceased to be
    toxic to its host and the host ceased to react as strongly to increased sexual needs and heightened sensory awareness-
    inevitable effects of the disease. The needed time was bought by new organisms of the same disease-new organisms
    introduced after significant adaptation had occurred. The new, unadapted organisms quickly spent themselves
    neutralizing the toxic wastes of the old. Thus, the new organisms had to be replaced frequently. The host body was a
    hostile environment for them-an environment already occupied, claimed, chemically marked by others of their kind.
    Their toxin-neutralization was merely their reflexive effort to survive in that hostile environment.
    But the original invading organisms had too much of a start. Or, if they were not well started, if the new organisms
    were introduced too soon, those new organisms simply became part of the original invasion, and the host, the patient,
    was no better, no worse.
    The meager statistics provided by the crew and the few experimental animals they managed to raise from frozen
    embryos seemed to support these findings. All four of the surviving crew members had been reinfected several times.
    There were no survivors among the first crew members stricken. These had been isolated and restrained. Their vital
    functions had been continually monitored and restored when they failed. But finally their brains had ceased to function.
    Reinfection was the answer, then-or an answer. A partial answer. Without it, everyone died. With it, some lived. Disa
    had died. Meda was obviously stronger. Perhaps she could live.
     
    PRESENT 8
     
    Meda brought Blake his bag when he asked for it and permitted him to examine her. She even permitted him to cleanse
    the scratches she had made on his arm and face, though she warned it would do no good. It had never done any good
    before when someone was infected, she said. The organisms were aggressive and fast. He had the disease.
    She or someone else had found and sabotaged