“SICK?” cried Bob anxiously. “What seems to be the trouble?” He and Mr. Holton had moved over to Joe.

“Got a terrible headache. Feel bad all over. My—my stomach doesn’t seem right.”

Almost at once the two naturalists grasped the meaning of Joe’s misfortune.

“There’s no doubt about it,” began Mr. Wallace, who was himself becoming pale. “You have mountain sickness, or soroche, as it’s called. I think I have a touch of it myself.”

“What causes it?” queried Bob.

“The high altitude,” Mr. Holton answered. “You see, when one makes a sudden change to nearly eleven thousand feet, it is a great strain on him. Usually, though, it doesn’t show up until reaching a much higher altitude than this. I’m surprised that Joe has it so soon.”

Joe did not become worse, but grew no better. One thing was apparent: until he would show improvement, he could not continue the journey.

Mr. Holton and Bob helped him into the cabin of the airplane, where an improvised bed was made.

“If it’s all right, I think I’ll stay with him,” announced Mr. Wallace. “I’m not feeling any too well myself, and then, too, Joe ought to have someone here with him.”

“All right,” said Karl. “Meanwhile the rest of us will go on into the city and have some gasoline sent out to the ’plane.”

In Quito the others found a filling station, the operator of which agreed to send out a truck to the monoplane to fill the tanks.

Back at the field they found that Joe had greatly improved and was anxious to fly on to Lima. It was evident that he had had only a slight attack.

In a short time the gasoline truck arrived, the tanks were replenished, and the explorers again climbed into the monoplane.

The journey to Lima promised to be more dangerous, as there were hazardous stretches of country to be left behind. But all knew that Karl was a skillful pilot. If he had not been he could not have brought them safely out of the terrible storm that they had encountered over the Caribbean.

Mountains, valleys, towns, then more mountains were spread before them as they flew on their way to the “City of the Kings.” The rugged Andes were more impressive than Bob and Joe had imagined.

At last they caught sight of Lima in the distance and before long were hovering over it.

Karl singled out Faucett’s Field and brought the monoplane down at high speed in order to avert a catastrophe. Well he knew that landing at such an altitude would present a difficulty, even at best.

“Can hardly feel the wheels touch the ground,” remarked Bob. “Wonder how Karl knows he’s made a landing?”

They were rolling swiftly over the smooth ground when suddenly Mr. Holton cried out in fright and pointed ahead at another airplane, which was landing directly in their path.

“Look out!” he warned Karl, speaking hoarsely through the transmitter.

Karl Sutman had already seen the danger and was cutting the monoplane to one side as best he could.

He was too late, however. The other airplane came on at sickening speed, heading directly at the explorers. The wings of the two crafts touched, and the monoplane sent the other machine, which was much lighter, spinning around dangerously.

Its lower wing scraped the ground, and a support was broken. A moment later it came to a stop, leaning on its side.

Meanwhile, Karl’s monoplane had continued farther, gradually losing speed until it came to a standstill several hundred feet away from the other airplane.

“A narrow escape!” breathed Joe, as he opened the door of the cabin and stepped out. “A little more and we would have been goners.”

“That crazy guy ought to have his face smashed!” snarled Karl, directing his glance at the distant airplane. “He broke one of the prime rules of flying: Never land when there is another ’plane on the field.”

“Here he comes now,” observed Bob. “Wonder what’s on his mind?”

They soon found out. The other aviator was a native Peruvian and could not speak English, but he addressed them angrily in the native language.

Karl stepped boldly up to the man. His fist shot out and caught the native squarely between the eyes.

The man reeled and then lost his balance, falling heavily to the ground.

At that moment two men from the airdrome came running out and demanded an explanation of what had happened.

Briefly Mr. Holton told them, stressing the fact that the aviator had not waited to land.

“He ought to have his pilot’s license taken away from him,” growled Karl Sutman, when the naturalist had concluded.

The men from the airdrome were greatly angered at the strange aviator for not being cautious in landing. They addressed him in no gentle terms as he lay on the ground.

Karl’s monoplane had been only slightly injured in the accident, but it was enough to require an hour of patient labor to make the repair.

The possibility of the other aviator doing damage to Karl’s machine prompted the tall young man to ask that it be kept under watch near the airdrome.

“Now suppose we walk on into Lima,” suggested Mr. Holton, after the ’plane had been rolled over to a safe place.

At the edge of the field was a wide street that led directly into the city. This the travelers followed and before very long came to the business district. In front of the huge cathedral they stopped to view the crowds through the cluster of palm trees that was before them.

“Quite a bit of life here,” observed Bob, as his eyes followed the busy swarm of people. “Lima must be a place of considerable importance.”

“It is,” said Mr. Holton. “It’s the capital of Peru.”

In the distance, beyond the plaza, a line of lofty mountains was plainly visible in the thin air. No doubt they were many miles away.

The explorers sat down idly on the wide steps of the cathedral.

“Now,” began Mr. Wallace, “we should make plans for the next two weeks. Mr. Lewis, we know, will arrive in Mollendo in about that time. What do you suggest doing—stay in the vicinity of Lima and take in the sights here, or fly on to Cuzco and the heart of Inca land?”

“I’d rather stay where we are for a while,” spoke up Karl. “There’s so much to see here that it will be worth it to spend a good bit of time in this section.”

“That goes for me, too,” came from Joe. “We’ll go to Cuzco later anyway, so why not see what we can around Lima?”

As everyone was in favor of doing this, they agreed to find a hotel and engage rooms.

“If I’m not mistaken, we won’t regret staying in this region,” said Bob Holton.

And they did not. During the next week and a half they spent their time taking in the sights of Lima and the rugged country surrounding it. They visited the botanical gardens, the various plazas, public buildings, streets, and the national museum. They toured the fascinating country about the city, seeing the ancient Inca highway, the mines of Morococha, the lifeless native huts that were everywhere, the marvelously engineered railroads, and the interesting city of Callao, located near by.

At the end of the time that they could spend here, the explorers were well pleased with the eventful days that had passed.

“Now to head for Mollendo,” said Mr. Holton, as one morning he arose early to prepare his possessions for the trip. “We’ve only got about a day before Mr. Lewis’s steamer arrives from the United States, and we must use the time to best advantage.”

The others were ready and climbed into the airplane for the long journey.

Mollendo, the adventurers found after the interesting flight, was much like other cities they had visited. It possessed a very interesting dock, however, which held the boys’ attention for many minutes.

The following day, when it became time for the steamship to arrive, they were on hand to meet the naturalist and the others.

“It’s coming!” cried Joe, pointing excitedly toward the horizon. “And will I be glad to see Dad!”

“I guess we all will,” said Mr. Wallace.

The vessel steamed closer and headed for the port. As it came toward them, the explorers could easily make out someone on the deck whom they recognized. It was Mr. Lewis.