He moved toward the door of the control-building, once more. Allison said somehow desperately:
"They'll have hidden their equipment. You'll never be able to find it!"
Calhoun shook his head in the starlight.
"Anything that can fly can spot it in minutes. Even on the ground one can walk almost straight to it. You see, something happened they didn't count on. That's why they've left it turned on at full power. The earlier, teasing uses of the cattle-fence were low-power. Annoying, to start with, and uncomfortable the second time, and maybe somewhat painful the third. But the last time it was full power."
He shrugged. He didn't feel like a long oration. But it was obvious. Something had killed the plants of a certain genus of which small species were weeds that destroyed Earth-type grasses. The ground-cover plants—and there were larger ones; Calhoun had seen one plant decaying in a florist's shop which had had to be grown in a cage—the ground-cover plants had motile stems and leaves and blossoms. They were cannibals. They could move their stems to reach, and their leaves to enclose, and their flowers to devour other plants. Perhaps small animals. The point, though, was that they had some limited power of motion. Earth-style sensitive plants and fly-catcher plants had primitive muscular tissues. The local ground-cover plants had them too. And the cattle-fence field made those tissues contract spasmodically. Powerfully. Violently. Repeatedly. Until they died of exhaustion. The full-power cattle-fence field had exterminated Mayan ground-cover plants all the way to the end of the east-bound highway. And inevitably—and very conveniently—also up to the exact spot where the cattle-fence field had begun to be projected. There would be an arrow-shaped narrowing of the wiped-out ground-cover plants where the cattle-field had been projected. It would narrow to a point which pointed precisely to the cattle-fence projector.
"Your friends," said Calhoun, "will probably give themselves up and ask for mercy. There's not much else they can do."
Then he said:
"They might even get it. D'you know, there's an interesting side effect of the cattle-fence. It kills the plants that have kept Earth-type grasses from growing here. Wheat can be grown here now, whenever and as much as the people please. It should make this a pretty prosperous planet, not having to import all its bread."
The ground-cars of the inhabitants of Maya City did begin to arrive at sunrise. Within an hour after daybreak, very savagely intent persons found the projector of ground-induction and hence cattle-fence fields. They turned it off. It was a very bulky piece of equipment, and it had been set up underground. It should have been difficult to find. But it wasn't.
By noon there was still some anger on the faces of the people of Maya, but there'd been little or no damage, and life took up its normal course again. Murgatroyd appreciated the fact that things went back to normal. For him it was normal to be welcomed and petted when the Med Ship Aesclipus Twenty touched ground. It was normal for him to move zestfully in admiring human society, and to drink coffee with great gusto, and to be stuffed with cakes and sweets to the full capacity of his expandable belly.
And while Murgatroyd moved in human society, enjoying himself hugely, Calhoun went about his business. Which, of course, was conferences with planetary health officials, politely receiving such information as they thought important, and tactfully telling them about the most recent developments in medical science as known to the Interstellar Medical Service.
PLAGUE ON KRYDER II
I
After Calhoun and Murgatroyd the tormal were established on board, the Med Ship Aesclipus Twenty allowed itself to be lifted off from Med Service Headquarters and thrust swiftly out to space. The headquarters landing grid did the lifting. Some five planetary diameters out, the grid's force fields let go and Calhoun busied himself with aiming the ship for his destination, which was a very long way off. Presently he pushed a button. The result was exactly the one to be expected. The Med Ship did something equivalent to making a hole, crawling into it, and then pulling the hole in after itself. In fact, it went into overdrive.
There were the usual sensations of dizziness, nausea, and a contracting spiral fall. Then there was no cosmos, there was no galaxy, and there were no stars. The Aesclipus Twenty had formed a cocoon of highly stressed space about itself which was practically a private sub-cosmos. As long as it existed the Med Ship was completely independent of all creation outside. However, the cocoon was active. It went hurtling through emptiness at many times the speed of light. The Aesclipus Twenty rode inside it. When the overdrive field—the cocoon—collapsed and the ship returned to normal space, it would find itself very far from its starting point. For every hour spent in overdrive, the ship should break out somewhat more than a light-year of distance farther away from Med Service Headquarters.
The background tape began to make its unobtrusive sounds. In overdrive, of course, the Med Ship was wholly isolated from the normal universe of galaxies and stars. There was, in theory, only one conceivable way in which it could be affected by anything outside its own overdrive field, and that had never happened yet. So there could have been a sepulchral, nerve-racking silence in the small spacecraft but for such sounds as the background tape provided.
Those were trivial, those sounds. One had to pay close attention to hear them. There was the sound of rain, and of traffic, and of wind in treetops and voices too faint for the words to be distinguished, and almost inaudible music—and sometimes laughter. The background tape carried no information; only the assurance that there were still worlds with clouds and people and creatures moving about on them.
But sensory assurance of the existence of a real cosmos is as essential to a man's subjective health as hormones and enzymes to his body. Calhoun would have suffered from the lack of such noises if they'd stopped, but he paid no attention to them when they began.
On this occasion the Med Ship stayed in overdrive for three long weeks, while the overdrive field hurtled toward the planet Kryder II. Calhoun was supposed to make a special public health visit there. Some cases of what the planetary government called a plague had turned up. The government was in a panic because plagues of similar type had appeared on two other worlds previously and done great damage. In both other cases a Med Ship man had arrived in time to check and stop the pestilence. In both cases the plague was not a new one, but a pestilence of familiar diseases. In both forerunners of this third plague, the arriving Med Ship's tormal had succumbed to the infection. So the government of Kryder II had called for help, and Calhoun and Murgatroyd answered the call. They were on the way to take charge.
Calhoun was singularly suspicious of this assignment. The report on the contagion was tricky. Typically, a patient was admitted to hospital with a case of—say—typhoid fever. It was a sporadic case, untraceable to any previous clinical one. The proper antibiotic was administered. With suitable promptness, the patient ceased to have typhoid fever. But he was weakened, and immediately developed another infectious disease. It might be meningitis. That yielded to treatment, but something else followed, perhaps a virus infection. The series went on until he died. Sometimes a patient survived a dozen such contagions, to die of a thirteenth. Sometimes he remained alive, emaciated and weak. No amount of care could prevent a succession of totally unrelated illnesses. Exposure or non-exposure seemed to make no difference. And the cause of this plague of plagues was undetectable.