So Ms heart beat high when he heard the door open. He turned, walking rapidly to meet them as they walked in.

"Gus old man." He held out his hand, wrung the other's. "And David boy!"

An hour passed. It was true night before they could stop speaking of themselves and turn to the universe.

It was David who broke out. He said, "I saw my first poisoning today, Uncle Hector. I knew enough to prevent panic. I wish I knew enough to prevent poisoning."

Conway said soberly, "No one knows that much. I suppose, Gus, it was a Martian product again."

"No way of telling, Hector. But a marplum was involved."

"Suppose," said David Starr, "you let me know anything I'm allowed to know about this."

"It's remarkably simple," said Conway. "Horribly simple. In the last four months something like two hundred people have died immediately after eating some Mars-grown product. It's no known poison, the symptoms are those of no known disease. There is a rapid and complete paralysis of the nerves controlling the diaphragm and the muscles of the chest. It amounts to a paralysis of the lungs, which is fatal in five minutes.

"It goes deeper than that too. In the few cases where we've caught the victims in time, we've tried artificial respiration, as you did, and even iron lungs. They still died in five minutes. The heart is affected as well. Autopsies show us nothing except nerve degeneration that must have been unbelievably rapid."

"What about the food that poisoned them?" asked David.

"Dead end," said Conway. "There is always time for the poisoned item or portion to be completely consumed. Other specimens of the same sort at the table or in the kitchen are harmless. We've fed them to animals and even to human volunteers. The stomach contents of the dead men have yielded uncertain results."

"Then how do you know it's food poisoning at all?"

"Because the coincidence of death after eating a Martian product time after time, without known exception, is more than coincidence."