Stone suddenly understood. "The child," he said. "It screamed.

"Yes."

"And the old fellow with the aspirin hyperventilated."

"Yes. And drank Sterno besides."

"And both of them shot their acid-base balance to hell," Stone said.

"Yes," Hall said. "My trouble was, I was hung up on the acidosis. I didn't understand how the baby could become acidotic. The answer, of course, was that it didn't. It became basic—too little acid. But that was all right—you could go either way, too much acid or too little—as long as you got out of the growth range of Andromeda."

He turned back to Burton. "All right now," he said. "Keep breathing rapidly. Don't stop. Keep your lungs going and blow off your carbon dioxide. How do you feel?"

"Okay," Burton panted. "Scared . . . but . . . okay."

"Good."

"Listen," Stone said, "we can't keep Burton that way forever. Sooner or later . . ."

"Yes," Hall said. "We'll alkalinize his blood."

To Burton: "Look around the lab. Do you see anything we could use to raise your blood pH?"

Burton looked. "No, not really."

"Bicarbonate of soda? Ascorbic acid? Vinegar?"

Burton searched frantically among the bottles and reagents on the lab shelf, and finally shook his head. "Nothing here that will work."

Hall hardly heard him. He had been counting Burton's respirations; they were up to thirty-five a minute, deep and full. That would hold him for a time, but sooner or later he would become exhausted—breathing was hard work—or pass out.

He looked around the lab from his vantage point. And it was while doing this that he noticed the rat. A black Norway, sitting calmly in its cage in a corner of the room, watching Burton.

He stopped.

"That rat . . ."

It was breathing slowly and easily. Stone saw the rat and said, "What the hell . . ."

And then, as they watched, the lights began to flash again, and the computer console blinked on:

EARLY DEGENERATIVE CHANGE IN GASKET V-112-6886

"Christ," Stone said.

"Where does that gasket lead?"

"It's one of the core gaskets; it connects all the labs. The main seal is—"

The computer came back on.

They looked at the screen in astonishment. "Something is wrong," Stone said. "Very wrong."

In rapid succession the computer flashed the number of nine more gaskets that were breaking down.

"I don't understand . . ."

And then Hall said, "The child. Of course!"

"The child?"

"And that damned airplane. It all fits."

"What are you talking about?" Stone said.

"The child was normal," Hall said. "It could cry, and disrupt it's acid-base balance. Well and good. That would prevent the Andromeda Strain from getting into its bloodstream, and multiplying, and killing it."

"Yes, yes," Stone said. "You've told me all that."

"But what happens when the child stops crying?"

Stone stared at him. He said nothing.

"I mean," Hall said, "that sooner or later, that kid had to stop crying. It couldn't cry forever. Sooner or later, it would stop, and its acid-base balance would return to normal. Then it would be vulnerable to Andromeda."