“When eaten by horses or cattle it is said to put them into deep sleep.  The Rockefeller Institute, I believe, is already making an analytical test of the grass.”

“Please talk so I can understand it,” begged Stacy.

“Yes; those words make my head ache,” scowled Ned.  “Even the guide is making up faces in his effort to understand.”

“He does understand.  He understands only too well.  For many years this grass has been known.  Cows turned out for the day would fail to return at night—­”

“To be milked,” interjected Stacy.

“And an investigation would disclose them sleeping in some region, where the sleepy grass grew

And the fat boy hummed: 

“Down where the sleepy grass is growing.”

“Travelers who have tied out their horses in patches of the grass for the night have been unable to continue their journey until the animals recovered from their strange sleep.  Thus the properties of the grass became known.”

“Indians use ’em to tame bad bronchos,” the guide informed them.

“Just so.”

“But, when will they wake up?” questioned Tad.

“Mebby sun-up to-morrow,” answered Juan, glancing up at the sky.

“What, sleep twenty-four hours?” demanded Ned.

“Si.”

“Preposterous.”

“Then, then, we’ve got to remain here all the rest of the afternoon and night—­ is that it?” demanded Tad.

“It looks that way.”

“And you knew about this stuff, Juan?” questioned Tad.

“Si.”

“Well, you’re a nice sort of a guide, I must say.”

“You ought to be put off the reservation,” threatened Stacy, shaking a menacing fist in front of the white teeth.

In the meantime, Tad had gone over to the animals again, and, taking them in turn, sought to stir them up.  He found he could not do so.  The ponies’ heads would drop to the ground after he had lifted and let go of them, just as if the animals were dead.

“Gives you a creepy feeling, doesn’t it?” shivered Walter.

“I should say it does,” answered Ned.

“Well, what is it, Chunky?” asked Tad, who observed that Stacy had something on his mind that he was trying to formulate into words.

“I’ve got an idea, fellows,” he exploded.

“Hold on to it, then.  You may never get another,” jeered Ned.

“What is it, Master Stacy?” asked the Professor.

“Then—­ then—­ then—­ that’s what Juan and his burro have been eating all the time.  I knew there was something the matter with them.”

A loud laugh greeted the fat boy’s suggestion.

“Guess he’s about right, at that,” grinned Tad.

“A brilliant thought,” agreed the Professor.  “Boys, I must have some of that grass.  I shall make some experiments with it.”

“Experiment on Chunky,” they shouted.

“No; he sleeps quite well enough as it is,” smiled the Professor.