“He actually took two tubes that must have had the right labels because he would have seen what they were marked.”
“Labels can be soaked off and transposed from one tube to another, Roger.”
“I think that happened. He took them, went up, and we both saw him use the hypodermic needle.”
“But—” Roger could hardly restrain his thrill at having made as clever a discovery as the coming one:
“Those two tubes—full!—are in back of others, right now. Not the two empty ones he incinerated to be sure the germs were all destroyed.”
“They are? How did you discover it?”
Roger told him: “Our chemical labels that are a green, photograph a darkish gray; and our culture labels, that are a buff, photograph lighter, but still grayer than white paper. The poisons are labeled red and come out in a picture almost black.
“But blue except very dark shades, will photograph nearly white! And those two labels, hidden in a dark corner, show up in the picture where they might not be noticed in the rack.”
“Can you go further and say why no culture was allowed to be given, although the inoculator evidently thought his serum was genuine?”
“Whoever was going to take the rats, did not want them to be dangerous to him.”