* * * * * The loud-speaker tuned to outside frequencies muttered again. Calhoun turned up its volume. "_Calling Headquarters_!" panted a voice. "_There's a mob of paras forming in the streets in the Mooreton quarter! They're raging! They heard the President's speech and they swear they'll kill him! They won't stand for a cure! Everybody's got to turn para! They won't have normals on the planet! Everybody's got to turn para or be killed!_" The grid operator looked up at the speaker. The ultimate of bitterness appeared on his face. He saw Calhoun's eyes on him and said savagely: "That's where I belong!" Murgatroyd headed straight for his cubbyhole and crawled into it. Calhoun got out a microscope. He examined the dried glass plates from the vacuum drier. The fractionator turned itself off and he focused on and studied the slide it yielded. He inspected a sample of the dust he'd gotten from the garments that had been sprayed at the south gate. The dust contained common dust particles and pollen particles and thread particles and all sorts of microscopic debris. But throughout all the sample he saw certain infinitely tiny crystals. They were too small to be seen separately by the naked eye, but they had a definite crystalline form. And the kind of crystals a substance makes are not too specific about what the substance is, but they tell a great deal about what it cannot be. In the fractionator slide he could get more information--the rate-of-diffusion of a substance in solution ruled out all but a certain number of compounds that it could be. The two items together gave a definite clue. Another voice from the speaker: "_Headquarters! Paras are massing by the north gate! They act ugly! They're trying to force their way into Government Center! We'll have to start shooting if we're to stop them! What are our orders?_" The grid operator said dully: "They'll wreck everything. I don't want to live because I'm a para, but I haven't acted like one yet. Not yet! But they have! So they don't want to be cured! They'd never forget what they've done. They'd be ashamed!" Calhoun punched keys on a very small computer. He'd gotten an index-of-refraction reading on crystals too small to be seen except through a microscope. That information, plus specific gravity, plus crystalline form, plus rate of diffusion in a fractionator, went to the stores of information in the computer's memory banks somewhere between the ship's living quarters and its outer skin. A voice boomed from another speaker, tuned to public-broadcast frequency: "_My fellow-citizens, I appeal to you to be calm! I beg you to be patient! Practice the self-control that citizens owe to themselves and their world, I appeal to you...._"