Even the hardy, swaggering half-breed seemed cowed.
I learned, however, that day once for all that both Summerlee and Challenger possessed that highest type of bravery, the bravery of the scientific mind.
Theirs was the spirit which upheld Darwin among the gauchos of the Argentine or Wallace among the head-hunters of Malaya.
It is decreed by a merciful Nature that the human brain cannot think of two things simultaneously, so that if it be steeped in curiosity as to science it has no room for merely personal considerations.
All day amid that incessant and mysterious menace our two Professors watched every bird upon the wing, and every shrub upon the bank, with many a sharp wordy contention, when the snarl of Summerlee came quick upon the deep growl of Challenger, but with no more sense of danger and no more reference to drum-beating Indians than if they were seated together in the smoking-room of the Royal Society's Club in St. James's Street.
Once only did they condescend to discuss them.
"Miranha or Amajuaca cannibals," said Challenger, jerking his thumb towards the reverberating wood.
"No doubt, sir," Summerlee answered. "Like all such tribes, I shall expect to find them of poly-synthetic speech and of Mongolian type."
"Polysynthetic certainly," said Challenger, indulgently.
"I am not aware that any other type of language exists in this continent, and I have notes of more than a hundred.
The Mongolian theory I regard with deep suspicion."
"I should have thought that even a limited knowledge of comparative anatomy would have helped to verify it," said Summerlee, bitterly.
Challenger thrust out his aggressive chin until he was all beard and hat-rim.
"No doubt, sir, a limited knowledge would have that effect.
When one's knowledge is exhaustive, one comes to other conclusions."
They glared at each other in mutual defiance, while all round rose the distant whisper,
"We will kill you—we will kill you if we can."
That night we moored our canoes with heavy stones for anchors in the center of the stream, and made every preparation for a possible attack.
Nothing came, however, and with the dawn we pushed upon our way, the drum-beating dying out behind us.
About three o'clock in the afternoon we came to a very steep rapid, more than a mile long—the very one in which Professor Challenger had suffered disaster upon his first journey.
I confess that the sight of it consoled me, for it was really the first direct corroboration, slight as it was, of the truth of his story.
The Indians carried first our canoes and then our stores through the brushwood, which is very thick at this point, while we four whites, our rifles on our shoulders, walked between them and any danger coming from the woods.
Before evening we had successfully passed the rapids, and made our way some ten miles above them, where we anchored for the night.
At this point I reckoned that we had come not less than a hundred miles up the tributary from the main stream.
It was in the early forenoon of the next day that we made the great departure.
Since dawn Professor Challenger had been acutely uneasy, continually scanning each bank of the river.
Suddenly he gave an exclamation of satisfaction and pointed to a single tree, which projected at a peculiar angle over the side of the stream.
"What do you make of that?" he asked.
"It is surely an Assai palm," said Summerlee.
It was an Assai palm which I took for my landmark.
The secret opening is half a mile onwards upon the other side of the river.
There is no break in the trees. That is the wonder and the mystery of it.
There where you see light-green rushes instead of dark-green undergrowth, there between the great cotton woods, that is my private gate into the unknown.
Push through, and you will understand."
It was indeed a wonderful place.
Having reached the spot marked by a line of light-green rushes, we poled out two canoes through them for some hundreds of yards, and eventually emerged into a placid and shallow stream, running clear and transparent over a sandy bottom.
It may have been twenty yards across, and was banked in on each side by most luxuriant vegetation.
No one who had not observed that for a short distance reeds had taken the place of shrubs, could possibly have guessed the existence of such a stream or dreamed of the fairyland beyond.
For a fairyland it was—the most wonderful that the imagination of man could conceive.
The thick vegetation met overhead, interlacing into a natural pergola, and through this tunnel of verdure in a golden twilight flowed the green, pellucid river, beautiful in itself, but marvelous from the strange tints thrown by the vivid light from above filtered and tempered in its fall.
Clear as crystal, motionless as a sheet of glass, green as the edge of an iceberg, it stretched in front of us under its leafy archway, every stroke of our paddles sending a thousand ripples across its shining surface.
It was a fitting avenue to a land of wonders.
All sign of the Indians had passed away, but animal life was more frequent, and the tameness of the creatures showed that they knew nothing of the hunter.
Fuzzy little black-velvet monkeys, with snow-white teeth and gleaming, mocking eyes, chattered at us as we passed.
With a dull, heavy splash an occasional cayman plunged in from the bank.
Once a dark, clumsy tapir stared at us from a gap in the bushes, and then lumbered away through the forest; once, too, the yellow, sinuous form of a great puma whisked amid the brushwood, and its green, baleful eyes glared hatred at us over its tawny shoulder.
Bird life was abundant, especially the wading birds, stork, heron, and ibis gathering in little groups, blue, scarlet, and white, upon every log which jutted from the bank, while beneath us the crystal water was alive with fish of every shape and color.
For three days we made our way up this tunnel of hazy green sunshine.
On the longer stretches one could hardly tell as one looked ahead where the distant green water ended and the distant green archway began.