"That place out there--" he considered us thoughtfully.
"Damned if I know what it is. Thought maybe it's gas--
of a sort. If it hadn't been for it we'd have been out of this
hole two days ago. I'm pretty sure it must be gas. And it
must be much less than it was this morning, for then we
made an attempt to get through again--and couldn't."

I was hardly listening. Ventnor had certainly advanced
a theory of our unusual symptoms that had not occurred
to me. That hollow might indeed be a pocket into which
a gas flowed; just as in the mines the deadly coal damp
collects in pits, flows like a stream along the passages. It
might be that--some odorless, colorless gas of unknown
qualities; and yet--

"Did you try respirators?" asked Dick.

"Surely," said Ventnor. "First off the go. But they
weren't of any use. The gas, if it is gas, seems to operate
as well through the skin as through the nose and mouth.
We just couldn't make it--and that's all there is to it. But
if you made it--could we try it now, do you think?" he
asked eagerly.

I felt myself go white.

"Not--not for a little while," I stammered.

He nodded, understandingly.