He saw it vividly for a moment, the long lines of cars creeping slowly forward.

And the signs by the side of the road. Speed limit 65 maximum, 40 minimum. They always seemed like a cruel joke at rush hour.

Maximum and minimum.

Cars that drove slowly were a menace. You had to keep traffic moving at a fairly constant rate, little difference between the fastest and the slowest, and you had to . . .

He stopped.

"I've been an idiot," he said.

And he turned to the computer.

In later weeks, Hall referred to it as his "highway diagnosis." The principle of it was so simple, so clear and obvious, he was surprised none of them had thought of it before.

He was excited as he punched in instructions for the GROWTH program into the computer; he had to punch in the directions three times; his fingers kept making mistakes.

At last the program was set. On the display screen, he saw what he wanted: growth of Andromeda as a function of pH, of acidity-alkalinity.

The results were quite clear:

ACIDITY OF MEDIUM AS LOG H - ION CONCENTRATION

CORRECTED FOR SKEW

MEANS, MODES, S.D. FOUND

IN CORREL/PRINT

MM - 76

CALL COORDINATES

O.Y.88.Z.09.

REVIEW CHECK

END PRINT

The Andromeda Strain grew within a narrow range. If the medium for growth was too acid, the organism would not multiply. If it was too basic, it would not multiply. Only within the range of pH 7.39 to 7.43 would it grow well.

He stared at the graph for a moment, then ran for the door. On his way out he grinned at his assistant and said, "It's all over. Our troubles are finished."

He could not have been more wrong.

28. The Test

IN THE MAIN CONTROL ROOM, Stone was watching the television screen that showed Burton in the sealed lab.

"The oxygen's going in," Stone said.

"Stop it," Hall said.

"What?"

"Stop it now. Put him on room air."

Hall was looking at Burton. On the screen, it was clear that the oxygen was beginning to affect him. He was no longer breathing so rapidly; his chest moved slowly.

He picked up the microphone.

"Burton," he said, "this is Hall. I've got the answer. The Andromeda Strain grows within a narrow range of pH. Do you understand? A very narrow range. If you're either acidotic or alkalotic, you'll be all right. I want you to go into respiratory alkalosis. I want you to breathe as fast as you can."

Burton said, "But this is pure oxygen. I'll hyperventilate and pass out. I'm a little dizzy now."

"No. We're switching back to air. Now start breathing as fast as you can."

Hall turned back to Stone. "Give him a higher carbon dioxide atmosphere."

"But the organism flourishes in carbon dioxide!"

"I know, but not at an unfavorable pH of the blood. You see, that's the problem: air doesn't matter, but blood does. We have to establish an unfavorable acid balance for Burton's blood."