always carry with us. They'd reached the contagious stage before I saw them—but all the kids are kept so quiet that nobody noticed that they were sick. They've certainly spread to each other and their nurses, and therefore out into your general population, all the infections needed for a first-rate multiple epidemic. And you've no doctors, no antibiotics—not even injectors to administer shots with if you had them."

"You're crazy!" cried young Walker. "Crazy! Isn't this a Phaedra trick to make us give in?"

"Phaedra's trick," said Calhoun more drearily than before, "is an atom bomb they're going to drop into this landing-grid—I suspect quarantine or no quarantine—in just two days more. Considering the total situation, I don't think that matters."

VI.

"... The most difficult of enterprises is to secure the co-operation of others in enterprises those others did not think of first...."

Manual, Interstellar Medical Service. P. 189.

Calhoun worked all night, tending and inspecting the culture incubators which were part of the Med ship's technical equipment. In the children's shelters, he'd swabbed throats. In the ship, he'd diluted the swabbings and examined them microscopically. He'd been depressingly assured of his very worst fears as a medical man—all of which could have been worked out in detail from the psych circuit system of child care boastfully described by Fredericks. He could have written out his present results in advance from a glance at the child Jak shown him by the younger Walker's wife. But he hated to find that objective information agreed with what he would have predicted by theory.

In every human body there are always germs. The process of good health is in part a continual combat with slight and unnoticed infections. Because of victories over small invasions, a human body acquires defenses against larger invasions of contagion. Without such constant small victories, a body ceases to keep its defenses strong against beach-heads of infection. Yet malnutrition or even exhaustion can weaken a body once admirably equipped for this sort of guerilla warfare.

If an undernourished child fails to win one skirmish, he can become overwhelmed by a contagion the same child would never have known about had he only been a little stronger. But, overwhelmed, he is a sporadic case of disease—a case not traceable to another clinical case. And then he is the origin of an 

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