“Positive,” said the chemist. “After we worked it out, it was pretty simple. The ‘poison’ was a chelating agent, that’s all. You saw the test run I did for you.”
The colonel nodded. He’d watched the little chemist add an iron salt to some of the fruit juice and seen it turn red. Then he’d seen it turn pale yellow when a magnesium salt was added. “But what’s a chelating agent?” he asked.
“There are certain organic compounds,” Dr. Petrelli explained, “that are … well, to put it simply, they’re attracted by certain ions. Some are attracted by one ion, some by another. The chelating molecules cluster around the ion and take it out of circulation, so to speak; they neutralize it, in a way.
“Look, suppose you had a dangerous criminal on the loose, and didn’t have any way to kill him. If you kept him surrounded by policemen all the time, he couldn’t do anything. See?”
The Space Service Officers nodded their understanding.
“We call that ‘sequestering’ the ion,” the chemist continued. “It’s used quite frequently in medicine, as Dr. Smathers will tell you. For instance, beryllium ions in the body can be deadly; beryllium poisoning is nasty stuff. But if the patient is treated with the proper chelating agent, the ions are surrounded and don’t do any more damage. They’re still there, but now they’re harmless, you see.”
“Well, then,” said the colonel, “just what did this stuff in the fruit do?”
“It sequestered the iron ions in the body. They couldn’t do their job. The body had to quit making hemoglobin, because hemoglobin needs iron. So, since there was no hemoglobin in the bloodstream, the patient developed sudden pernicious anemia and died of oxygen starvation.”
Colonel Fennister looked suddenly at Dr. Smathers. “I thought you said the blood looked normal.”
“It did,” said the physician. “The colorimeter showed extra hemoglobin, in fact. But the chelating agent in the fruit turns red when it’s connected up with iron—in fact, it’s even redder than blood hemoglobin. And the molecules containing the sequestered iron tend to stick to the outside of the red blood cells, which threw the whole test off.”