"The ideal scientific mind," continued Challenger--"I put it in the third person rather than appear to be too self-complacent--the ideal scientific mind should be capable of thinking out a point of abstract knowledge in the interval between its owner falling from a balloon and reaching the earth. Men of this strong fibre are needed to form the conquerors of nature and the bodyguard of truth." "It strikes me nature's on top this time," said Lord John, looking out of the window. "I've read some leadin' articles about you gentlemen controllin' her, but she's gettin' a bit of her own back." "It is but a temporary setback," said Challenger with conviction. "A few million years, what are they in the great cycle of time? The vegetable world has, as you can see, survived. Look at the leaves of that plane tree. The birds are dead, but the plant flourishes. From this vegetable life in pond and in marsh will come, in time, the tiny crawling microscopic slugs which are the pioneers of that great army of life in which for the instant we five have the extraordinary duty of serving as rear guard. Once the lowest form of life has established itself, the final advent of man is as certain as the growth of the oak from the acorn. The old circle will swing round once more." "But the poison?" I asked. "Will that not nip life in the bud?" "The poison may be a mere stratum or layer in the ether--a mephitic Gulf Stream across that mighty ocean in which we float. Or tolerance may be established and life accommodate itself to a new condition. The mere fact that with a comparatively small hyperoxygenation of our blood we can hold out against it is surely a proof in itself that no very great change would be needed to enable animal life to endure it." The smoking house beyond the trees had burst into flames. We could see the high tongues of fire shooting up into the air. "It's pretty awful," muttered Lord John, more impressed than I had ever seen him. "Well, after all, what does it matter?" I remarked. "The world is dead. Cremation is surely the best burial." "It would shorten us up if this house went ablaze." "I foresaw the danger," said Challenger, "and asked my wife to guard against it." "Everything is quite safe, dear. But my head begins to throb again. What a dreadful atmosphere!" "We must change it," said Challenger. He bent over his cylinder of oxygen. "It's nearly empty," said he. "It has lasted us some three and a half hours. It is now close on eight o'clock. We shall get through the night comfortably. I should expect the end about nine o'clock to-morrow morning. We shall see one sunrise, which shall be all our own." He turned on his second tube and opened for half a minute the fanlight over the door. Then as the air became perceptibly better, but our own symptoms more acute, he closed it once again.