THE sight that the explorers beheld was unpleasant to the extreme. Scarcely had Joe uttered the cry of horror when the organ suddenly fell, pushing one of the natives over the cliff.

The man screamed in terror and then disappeared into the depths below. It was thousands of feet to the bottom of the abyss, and instant death was almost certain.

Bob drew back from the brink with a shudder. Joe and Dr. Rander gave cries of repugnance. The other Indians screamed hoarsely, uttering something that only Dr. Rander understood.

The natives ran wildly down the trail, scowling and making gestures.

“Terrible!” muttered the old explorer, when they had disappeared around a turn.

“What did they say?” inquired Joe, who had been struck by the Indians’ attitude of anger.

“They intend to kill the man who wanted the organ,” Dr. Rander told him. “They blame the Indian’s death on him.”

“Well, of all things!” exclaimed Joe indignantly. “Isn’t there anything we can do about it?”

The old man shook his head.

“When they set their minds on anything there’s no use trying to change them,” he said hopelessly.

“We might warn the man whom they intend to kill,” suggested Bob Holton.

“Don’t know who it is,” Dr. Rander returned. “And the Indians wouldn’t tell us.”

Bob and Joe all during that day felt that something could have been done to prevent the natives from killing the plantation owner, or whoever it was that was getting the organ. They were not a little vexed at Dr. Rander for treating the matter so lightly.

“But then,” said Bob hopefully, “maybe the Indians didn’t get away with it.”

Ten minutes later the youths forgot about the incident. They had been struggling over an exceedingly rough stretch when they suddenly came to another river, much wider than the one they had seen several days previously.

“Have to ford it, I guess,” said Joe Lewis. “No other way across.”

Again the boys put on their hip boots, and again they plunged into the water, driving the mules before them. The going here was difficult, as the current was rather strong, and the mules had to be watched more closely.

They were about halfway across when the old explorer cried out in fright.

“Help!” His voice was wild with terror.

“What is it?” demanded Joe, who was nearest him.

Then the youth saw. Dr. Rander was rapidly sinking into a hole. Already the water had reached his chest, and he was going down rapidly.

Joe at once put thought into action. He dashed over to one of the mules, opened a bag, and began searching about for a rope.

Frantic with the delay, the youth worked his hand like a machine, feeling in every corner of the bag. What if he could not find the rope?

But fortune was with him. In another bag on the opposite side of the mule he found the rope. Luckily it was not tangled.

Joe was almost afraid to turn for fear Dr. Rander would be gone. His heart gave a leap as he saw that the explorer’s head was still above the water.

“Here, get hold of this,” Joe called, throwing the rope over to the old man. “Now come on, Bob. Let’s pull.”

This last was unnecessary, as Bob was already on the spot waiting to catch hold of the rope.

“Steady, now!”

Slowly the youths pulled their friend out of the heavy mud, which oozed ominously as it released its victim. Once it seemed as if the old man would have to release his hold, but he managed to hang on desperately.

At last, when he was completely out of the mud, he moved over to his young companions and gazed at them gratefully.

“You did wonderful,” he commended. “Many people would have acted more slowly—and I would have gone under.”

“Wonder if there are any more treacherous places like that?” Bob scanned the chocolate water closely, as if by instinct to detect any dangerous spots.

“We’ll have to risk it,” Joe said. “It might be well to spread apart, so if anyone gets caught, the others can come to his rescue.”

“Good suggestion,” praised Bob. “I’ll get away over to this side.”

But if there were any more mud holes the explorers failed to come across them, and finally reached the other side safely, driving the mules before them.

On the bank Dr. Rander took off his mud-soaked clothes and replaced them with dry ones. Then, after a short rest, they resumed the journey.

“Who’s coming?” Joe strained his ears to make out the source of footsteps.

Then, rounding a growth of stunted trees, appeared a long caravan of small llamas, which were heavily loaded with what was probably firewood. Beside the curious animals walked two Indians, wearing the common “pancake” hats.

Luckily there was enough room for both cavalcades to pass freely, and they experienced no difficulty.

The natives stopped for a few minutes and conversed with Dr. Rander, who spoke Quichua freely. Then they started down the trail, driving the llamas at a rapid pace.

“Funny animals,” observed Bob when they had gone. “I was afraid all the time one or two would come at me and spit in my face, like the one back at Cuzco.”

Joe laughed.

“As long as you don’t bother them, I guess they’re all right,” he said. “But from what I’ve heard, they don’t like to be played with.”

“Don’t I know it!” grinned the other youth.

Before long they saw the origin of the llama caravan. Set back from the path was a large mud hut, about which played several Indian children. Another man and a woman came out to meet the adventurers.

Again Dr. Rander stopped to converse in the Quichua tongue. But not for long. He was anxious to lose no time in getting to the secrets. Even at best it would require many, many days.

“Hope we don’t have any trouble from now on,” said Joe, as he followed the old man up a steep slope. “But I suppose we will.”

Bob nodded.

“Exploring has its difficulties,” he said. “It will be funny if we don’t have any more things happen to delay us.”

That evening they camped in a little valley between two high peaks. All were glad to rest their tired limbs after such an arduous day over rocky paths.

At a small gurgling spring but a short distance away they drank freely and filled their canteens to capacity. Then, refreshed and ready to prepare the meal, they were about to head for the tent when Dr. Rander noticed something coming at them. He turned about quickly, his face white with fear.

The youths saw the danger and ran toward the mules as fast as they could.

Advancing toward them was a heavy swarm of green jungle flies, whose bite all knew to be poisonous as well as annoying. If the flies attacked the explorers, the result would be marks and red, swollen scratches that would disappear only after several weeks of patient treating.

“The mosquito nets—quick!” cried Dr. Rander, opening a pack and fumbling about nervously. “We must have them! That swarm of flies is so large that there won’t be anything left of us!”

But the adventurers were not quick enough. Before they could get out the nets the buzzing flies were upon them, biting their faces and arms severely. The little insects even penetrated the heavy clothing in a determined effort to satisfy their thirst for blood.

“This is awful!” groaned Bob, working feverishly to find a net.

Scarcely would they put a hand into the packs when they would have to remove it and slap away the flies, the marks of which already pained severely.

At last Joe found the pack that contained the nets, and lost no time in distributing the latter among his friends and himself.

“Now let them come,” challenged Bob, facing the swarm angrily. “I guess it won’t do ’em any good now.”

But even with the protection afforded by the closely woven nets, the menacing little creatures bit the explorers’ arms and legs most annoyingly.

Relief did not come until dark. The blackness of the night served in some manner to cause the flies to leave, although a small few remained threateningly.

“Oh!” muttered Bob, trying in vain to bend his wrist. “They sure fixed us up plenty good. Our—— My gosh! Joe, look at yourself in a mirror. And you, too, Dr. Rander.”

The three were indeed a sorry-looking sight. Their faces were so swollen that their eyes were hardly visible, and their hands and arms were no better off.

“And how it hurts!” Joe was almost frantic with the stinging pain. “It’s a good thing the sun went down when it did, or there would have been nothing left of us,” he added.

All were too bruised and tired to prepare a meal, but necessity forced them to do so. But not until Dr. Rander produced a large tube of a special salve, which he applied freely to the swollen parts.

“This will relieve the pain,” he told the youths. “In the morning we’ll be a little better, but it won’t be for a week that the sores will disappear completely.”

Dawn found the adventurers scarcely aware that they had been bitten, although the scars were still there to tell the story.

“Let’s forget all about that unpleasant encounter,” suggested Joe optimistically. “Suppose we take everything that happens purely as an adventure.”

“Now you’re talking!” Bob patted his chum on the back. “We came here for adventure, and we mustn’t kick when we get it.”

Along toward noon Bob was lucky in bringing down a wild duck, which flew from a jungle not far away. Roasted over a fire, it proved good eating, despite the fact that it was tough.

Dinner—for that was what the youths called the noon meal when they were on exploration trips—over, they took it easy in the shade of a group of stunted trees, which grew almost straight out from the mountainside.

“Trail’s pretty bad,” observed Joe, his eyes on what could be seen of the narrow path as it circled up the peak. “But I suppose it’s nothing to what we’ll find it later on.”

Which proved fairly accurate, as they later observed. At times the trail was so rough and rocky that it was with greatest difficulty that the mules were able to clamber up the steep elevations. On one occasion it was necessary for the mules to jump up a three-foot rock, which obstructed the trail dangerously near a five-hundred-foot drop.

“Steady, now,” cautioned the old man, helping the youths unload the mules. “If we make a misstep, it will prove our finish.”

None of the explorers did, fortunately. But one of the mules was not as lucky. It was the last animal in the line and had been carrying only trifles that were not of necessity to the explorers.

The other mules had safely jumped to the top of the rock and were grazing on the thin patches of grass that grew on the mountainside.

“Hurry, now,” came from Joe. “Let’s get this last fellow up.”

Scarcely had the words left his mouth when the unfortunate animal lost its footing and, balancing for a moment at the edge of the canyon, plunged helplessly over the brink.

“Gone!” Dr. Rander could hardly believe the fact.

Bob and Joe had watched the accident tensely, unable to render any assistance to the terrified mule. At last they climbed up on the rock with a resolution to take matters as they were.

“Talk about adventure,” said Bob with a grim smile. “I guess we’re getting plenty of it.”

“Just wait,” murmured Joe meaningly. “This won’t be anything to what’s coming, or else I’ll miss my guess.”

“I sincerely hope nothing else will happen today,” Dr. Rander said. “I wish to get beyond this short range of mountains before nightfall.”

They later saw that traveling was so slow that it would be impossible to do this. But they were well on the other side of the peaks when darkness overtook them.

“Now to make camp,” sang Bob, tethering the foremost mule to a stout crag.

“Wait,” called Joe, who was just out of sight around a turn.

“What for?”

“Because—I’ve found something. Come here.”

Bob and Dr. Rander went around the bend, where Joe was waiting for them.

“It’s a cave,” explained the youth. “A big cave. Let’s see what’s in it.”

“Better be careful,” was the old man’s warning. “It isn’t unlikely that some snake has its lair here.”

They went in cautiously, Joe holding his flashlight and Bob his revolver. How far the opening extended they had not the slightest idea, for the light beam did not reach the other end.

Suddenly Joe shrank back, as his light rested on something not thirty feet ahead.

“Bats!” he cried. “Vampire bats! And they’re coming toward us!”