"A biochemist." Alcala tried to see past the meditative mask of the thin dark face. "He makes small job-lots of chemical compounds. Special bug spray for sale to experimental plantations, hormone spray for fruits, that sort of thing. Sometimes, when he collects some money ahead, he does research." Camba waited, and his silence became a question. Alcala spoke reluctantly, anger rising in him. "Oh, it's genuine research. He has some patents and publications to his credit. You can confirm that if you choose." He was unable to keep the hostility out of his voice. A waiter came and placed steaming platters of food on the table. Camba waited until he was gone. "You know him well, I presume. Is he sane?" The question was another shock. Alcala thought carefully, for any man might be insane in secret. "Yes, so far as I know." He turned his attention to the steak, but first took three very large capsules from a bottle in his pocket. "I would not expect that a doctor would need to take pills," Camba remarked with friendly mockery. "I don't need them," Alcala explained. "Mixed silicones. I'm guinea pigging." "Can't such things be left to the guinea pigs?" Camba asked, watching with revulsion as Alcala uncapped the second bottle and sprinkled a layer of gray powder over his steak. "Guinea pigs have no assimilation of silicones; only man has that." "Yes, of course. I should have remembered from your famous papers, _The Need Of Trace Silicon In Human Diet_ and _Silicon Deficiency Diseases_." * * * * * Obviously Camba had done considerable investigating of Alcala before approaching him. He had even given the titles of the research papers correctly. Alcala's wariness increased. "What is the purpose of the experiment this time?" asked the small dark Federation agent genially. "To determine the safe limits of silicon consumption and if there are any dangers in an overdose." "How do you determine that? By dropping dead?" He could be right. Perhaps the test should be stopped. Every day, with growing uneasiness, Alcala took his dose of silicon compound, and every day, the chemical seemed to be absorbed completely--not released or excreted--in a way that was unpleasantly reminiscent of the way arsenic accumulated without evident damage, then killed abruptly without warning. Already, this evening, he had noticed that there was something faulty about his coordination and weight and surface sense. The restaurant door had swung back with a curious lightness, and the hollow metal handle had had a curious softness under his fingers. Something merely going wrong with the sensitivity of his fingers--? He tapped his fingertips on the heavy indestructible silicone plastic table top. There was a feeling of heaviness in his hands, and a feeling of faint rubbery _give_ in the table.