"No, it's still oxygen, Colonel, but not the way your pack handles it. You see, Dr. Lurie has figured out a way to use atomic, not molecular, oxygen--O instead of O_{2}, if you follow me--and to give it by injection in a highly concentrated form. As you see, we're not wearing oxygen packs any more." "So I noticed. But I'm afraid your little hoax can't go on very long. In another two minutes, my friends, you'll be gasping like fish and running frantically home to get those pesky oxygen packs." "Why don't you time us?" Baker sipped his coffee. "I _am_ timing you, my friends. There are certain principles of physiology that can't be contravened. We're at the oxygen equivalent of a 27,000-foot elevation. The average duration of useful consciousness is two and a half minutes." Baker sipped his coffee, watching the faces of the two men. The clock on his desk moved past two minutes. Two and a half minutes. Baker shrugged. He knew there were some exceptions. Some persons in superior physiological condition had proved in aeronautical tests on Earth to be able to go on for as long as four minutes in as rarefied oxygen as existed here. But no more than four minutes. The clock hand reached four minutes. The men still sat there. He had timed them wrong. He had missed a minute. Certainly. They were going to start sagging now. Now. Another minute went by. Another minute. The men sat there, looking straight at him through the tele-screen. There was a cynical smile on their faces, as if they knew the camera was on them--as if they could actually see him. Another minute passed. Another minute. Baker leaped to his feet. "Die, damn you!" he screamed. The two men burst into laughter that exploded all over the screen. With a curse, Baker switched off the set and stood there, breathing hard. A moment later, he flicked it on again. The two men were leaving the booth. "Come back," he yelled. They turned, part way. Their indifference was maddening. "Come up here," Baker commanded. "I want to see your invention. I want to buy it." "Not interested." "Damn you, you must!" Baker shouted, his heart beating furiously. His hypnotized eyes kept swinging back to the clock. At least eleven minutes had passed! "We're not walking into any trap, Colonel," Harvey Flanders said. "If you want to do any dickering, you'll have to come see us. You know where to get us if you want us." The two men started up the road. Baker watched them with sick eyes as they went with firm steps to Harvey Flanders' house, and disappeared inside the doorway. * * * * * Inside Harvey Flanders' doorway, Dr. Lurie staggered. Harvey caught him, but didn't have the strength to hold him, and both sagged to the floor. "Quick, Ruth," Harvey said, gasping. She was waiting with the oxygen packs. Red Brace was with her. They fitted the masks quickly over the faces of the two men on the floor, and anxiously watched their rapid, intense breathing.