He tried another and another, and then another; every one of the tubes was empty.
"Now what in the world do you make of that ?" he asked.
The tubes had yet to be filled and there was no hint of what they were to be filled with.
"What I am wondering about is why they troubled to send the tubes at all ?" said Fairbairn slowly.

"There's some reason, of course, something perhaps in the make of the glass." He held one of the tubes up to the light.

There was nothing to distinguish it from any one of the tubes in which small tabloids are sold by chemists.
Hillyard got out of his bureau the letter in which these tubes were mentioned.
"'They have been successful in France,'" he said, quoting from the letter.

"The scientists may be able to make something of them in Paris.
This letter and the tubes together may give a clue.

I think that I had better take one of the boxes to Paris." "Yes," said Fairbairn gloomily.