He moved cautiously among its streets. Here and there he saw a sign, "Quarantine." He nodded. Things had gotten really bad! Normal sanitary measures would prevent the spread of contagion of a normal kind. When infections led to the quarantine of every house where plague appeared, it meant that doctors were getting panicky and old-fashioned. However, the ideas of the causes of pestilences would remain modern. Nobody would suspect an epidemic of being actually a crime.
He found a merchandise center. He found a food shop. All the night was dark and silent. He listened for a long, long time, and then committed burglary.
With his hand lamp turned down to the faintest of glimmers, he began to accumulate parcels. There was plague in this area and this town. Therefore, he painstakingly picked out parcels of every variety of foodstuff in the food shop's stock. He stuffed his loot into a bag. He carried everything, even salt and sugar and coffee, meat, bread, and vegetables in their transparent coverings. He took a sample—the smallest possible—of everything he could find.
He piously laid an interstellar currency note on the checkout desk. He left. He went back to the highway by which he'd arrived. He trudged four miles to where a pellet designed for something else made a distinctive patch of unpleasant smell. He turned and traveled by compass until he found another evil-smelling spot. Again by compass . . . and he arrived back at the Med Ship. He went in.
Murgatroyd greeted him with inarticulate cries, embracing his legs and protesting vehemently of his sufferings during Calhoun's absence. To keep from stepping on him, Calhoun tripped. The bag of his burglarized acquisitions fell. It broke. Something smashed.
"Stop it!" commanded Calhoun firmly. "I missed you too. But I've got work to do, and I didn't run across any ditch water. I've got to go out again."
He forcibly prevented Murgatroyd from going with him, and he spent an hour fumbling for a swampy spot in the dark forest. In the end he packed up damp and half-rotted woods-mold. He carried that back to the ship. Then he began to collect the grocery packages he'd dropped. A package of coffeebeans had broken.
"Damn!" said Calhoun.
He gathered up the spilled beans. Murgatroyd assisted. Murgatroyd adored coffee. Calhoun found him popping the beans into his mouth and chewing in high delight.
He went about the essential, mundane labor he'd envisioned. He prepared what a physician of much older times would have called a decoction of rotted leaves. He examined it with a microscope. It was admirable! There were paramecia and rotifers and all sorts of agile microscopic creatures floating, swimming, squirming and darting about in the faintly brownish solution.
"Now," said Calhoun, "we will see if we see anything."
He put the fraction of a drop of a standard and extremely mild antiseptic on the microscope slide. The rotifers and the paramecia and the fauna of the ditch water died. Which, of course, was to be expected. Single-celled animals are killed by concentrations of poison which are harmless to greater animals. Antiseptics are poisons and poisons are antiseptics, but antiseptics are poisons only in massive doses. But to a rotifer or to paramecia all doses are massive.
"Therefore," explained Calhoun to a watching and inquisitive Murgatroyd, "I act more like an alchemist than a sane man. I feel apologetic, Murgatroyd. I am embarrassed to make decoctions and to mix them with synthesized ditch water. But what else can I do? I have to identify the cause of the plague here, without having contact with a single patient because Doctor Kelo . . ."
He shrugged and continued his activities. He was making solutions, decoctions, infusions of every kind of foodstuff the food shop he'd burglarized contained. The plague was not caused by an agent itself in infections. It was caused by something which allowed infections to thrive unhindered in human bodies. So Calhoun made soups of meat, all the kinds of meat, or grain and grain products, and vegetables taken from their transparent coverings. Even such items as sugar, salt, pepper and coffee were included.
Those solutions went upon microscope slides, one by one. With each, in turn, Calhoun mingled the decoction of rotting vegetation which was, apparently, as well-suited for his research as stagnant water from a scummy pond. The animalcules of the decoction appreciated their diverse food supplies. They fed. They throve. Given time, they would have multiplied prodigiously.
Eventually Calhoun came to the solution of coffee. He mixed it with his experimental microscope-animal zoo, and the paramecia died. Rotifers ceased to whirl and dart about upon their sub-miniature affairs. When an infusion of coffee from the food shop was added to the liquid environment of one-celled animals, they died.
Calhoun checked. It was so. He made an infusion of coffee from the Med Ship's stores. It was not so. Coffee from the ship was not fatal to paramecia. Coffee from the shop was. But it would not follow that coffee from the shop would be fatal to humans. The alcoholic content of beer is fatal to paramecia. Wine is a fair antiseptic. No! The food store coffee could very well be far less toxic than the wildest of mouthwashes, and still kill the contents of Calhoun's ditch-water zoo.
However, the point was that something existed which allowed infections to thrive unhindered in human bodies. Something destroyed the body's defenses against infections. Nothing more would be needed to make the appearance of a plague. Every human being carries with him the seeds of infection, from oral bacteria to intestinal flora, and even often streptococci in the hair follicles of the skin. Destroy the body's means of defense and anyone was bound to develop one of the diseases whose sample bacteria he carries about with him.
Instantly one ceased to think of the plague on Kryder II—and Castor IV before it—instantly one ceased to think of the epidemic as an infection miraculously spreading without any germ or bacterium or virus to carry it, instantly one thought of it as a toxin only, a poison only, a compound as monstrously fatal as the toxin of—say—the bacillus clostridium botulinum. Immediately everything fell into place. The toxin that could simulate a plague could be distributed on a foodstuff: grain or meat or neatly packaged coffee. It would be distributed in such dilution that it was harmless. It would not be detected by any culture-medium process. In such concentration as humans would receive, it would have one effect, and one effect only. It would hinder the body's formation of antibodies. It would prevent the production of those compounds which destroy infective agents to which human beings are exposed. It would simply make certain that no infection would be fought. Antibodies introduced from outside could cure a disease the body could not resist, but there would always be other diseases. . . . Yet, in a concentration greater than body fluids could contain, it killed the creatures that thrived in ditch water.
Calhoun consulted the slip of paper the computer had printed out for him. He went down to the ship's stores. A Med Ship carries an odd assortment of supplies. Here were the basic compounds from which an unlimited number of other compounds could be synthesized. With the computer-slip for a prescription form, he picked out certain ones. He went back to the ditch-water samples presently. He worked very painstakingly. Presently, he had a whitish powder. He made a dilute—a very dilute solution of it. He added that solution to ditch water. The paramecia and rotifers and other tiny creatures swam about in bland indifference. He put in a trace of coffee decoction. Presently, he was trying to find out how small a quantity of his new solution, added to the coffee infusion, made it harmless to paramecia.
It was not an antidote to the substance the coffee contained. It did not counter the effects of that monstrously toxic substance, but it combined with that substance. It destroyed it; it was the answer to the plague on Kryder II.