 Why is Macklin's reaction to the shot alarming?
But Macklin is exactly what we need for a quick, dramatic test. "I would have said the common cold," Macklin replied, "but I suppose from what you have said you mean headaches." "Aspirins would still be used to reduce fever and relieve muscular pains," Mitchell said. Ferris and I are confident that there is no danger.... By established periodic cycle he should be suffering hell right now, shouldn't he? "What do you mean by that, Mrs. Macklin," Mitchell said sharply. "What could be wrong with Macklin?" he asked without removing his hand from the telephone. "Mrs. Macklin," Mitchell said quickly, "I'm sure we can help if there is anything wrong with your husband.
 The shot has somehow removed his intelligence.
 He's acting as if he took a narcotic, enough that Mrs. Macklin suspects that they gave him heroin?  He's much too happy, as observed by Sidney. He's inexplicably healthy and too adjusted.  He seems unbothered by it, despite the fact that it should have changed his life.  The shot has somehow removed his intelligence.