 Why do they want Macklin specifically to be the test subject?
But Macklin is exactly what we need for a quick, dramatic test. "When we prove our results that should be of enough practical value for anyone. Our reputations don't go outside our own fields," Mitchell said. "But now Macklin—" Elliot Macklin had inherited the reputation of the late Albert Einstein in the popular mind. He was the man people thought of when the word "mathematician" or even "scientist" was mentioned. No one knew whether his Theory of Spatium was correct or not because no one had yet been able to frame an argument with it. The government took up a lot of his time using him as the symbol of the Ideal Scientist to help recruit Science and Engineering Cadets. For the past seven years Macklin—who was the Advanced Studies Department of Firestone University—had been involved in devising a faster-than-light drive to help the Army reach Pluto and eventually the nearer stars. Mitchell had overheard two coeds talking and so knew that the project was nearing completion. "Actually, Doctor, we haven't the right to ask this of a man of your importance. "Doctor, we understand you have severe headaches," Mitchell said. "No, Harold, it isn't," Macklin admitted. "Doctor," Mitchell said, "what would you say the most common complaint of man is?" "I would have said the common cold," Macklin replied, "but I suppose from what you have said you mean headaches." "Everybody has them at some time in his life. "Aspirins would still be used to reduce fever and relieve muscular pains," Mitchell said. "There are a number of different causes for headaches—nervous strain, fatigue, physical diseases from kidney complaints to tumors, over-indulgence—but there is one effect of all of this, the one real cause of headaches," Mitchell announced. "The pressure effect caused by pituitrin in the brain," Mitchell said eagerly. "That is, the constriction of blood vessels in the telencephalon section of the frontal lobes. It's caused by an over-production of the pituitary gland. We have artificially bred a virus that feeds on pituitrin." "In certain areas it is valuable to have a constriction of blood vessels." "The virus," Ferris explained, "can easily be localized and stabilized. A colony of virus in the brain cells will relax the cerebral vessels—and only the cerebral vessels—so that the cerebrospinal fluid doesn't create pressure in the cavities of the brain."
 He is a man of great importance, and people will believe him if it works.
 As a fellow scientist, he'd understand and appreciate what they're doing.  He's in relatively good health, meaning he'd survive the experiment and yield resutls.  He is a man of great importance, and people will believe him if it works.  He has chronic migraines, making him a good candidate.