Page:The Poison Belt - Conan Doyle, 1913.djvu/118

 Rh  and the sound of the loud hissing fell away till it was the most gentle sibilation.

"We must husband our supply of the gas," said he. "The atmosphere of the room is now strongly hyper-oxygenated, and I take it that none of us feel any distressing symptoms. We can only determine by actual experiments what amount added to the air will serve to neutralize the poison. Let us see how that will do."

We sat in silent nervous tension for five minutes or more, observing our own sensations. I had just begun to fancy that I felt the constriction round my temples again when Mrs. Challenger called out from the sofa that she was fainting. Her husband turned on more gas.

"In pre-scientific days," said he, "they used to keep a white mouse in every submarine, as its more delicate organization gave signs of a vicious atmosphere before it was perceived by the sailors. You, my