Juan pointed to the place where the stock had been tethered after they arrived at the camp.

There was not an animal to be seen anywhere on the plain.

“Gone!” gasped the lads, with sinking hearts.

“No, no, no.  There!” stammered the guide.

With one accord the boys ran at top speed to the spot indicated by Juan.

There, stretched out in the long grass lay bronchos and burros.

“They’re dead, the ponies are dead, every one of them!” cried the lads aghast.

CHAPTER IX

 The midnight alarm

“What’s this, what’s this?” demanded the Professor, striding up.

“Look!  Look!  The ponies are dead!” exclaimed Ned excitedly.

“What do you suppose could have happened to them?” stammered Walter.

“Is it possible?  What’s the meaning of this, guide?”

Juan shrugged his shoulders and showed his white teeth.

In the meantime Tad had hurried to his own pony, and was down on his knees examining it.  Placing his hands on the animal’s side, he remained in that position for an instant, then sprang up.

“They’re not dead, fellows!  They’re alive!”

“Asleep,” grumbled Ned disgustedly.

“But there’s something the matter with them.  Something has happened to the stock,” added Tad.

“Only a false alarm,” nodded Stacy.

“Think so?  Try to wake your pony up,” advised Tad.

Stacy had already hurried to his own broncho, and now began tugging at the bridle rein, with sundry pokes in the animal’s ribs.

“I can’t.  He’s in a trance,” wailed Stacy, considerably startled.

That expression came nearer to describing the condition of the stock than any other words could have done.

“Guide, what do you know about this?” questioned the Professor.  “Has some one been tampering with our animals?”

Juan shrugged his shoulders with an air of indifference.

“No bother bronchs.”

“Then will you please tell us what is the matter with them?”

“Sleepy grass!”

“Sleepy grass?” chorused the lads.

“Of course they’re asleep all right,” added Ned.  “But whoever heard of sleepy grass?”

“He means they’re sleeping on the grass,” Stacy informed them.

“Ah!  I begin to understand,” nodded the Professor.  “I think I know what the trouble is now.  The guide is no doubt right.”

The boys gathered around him, all curiosity.

“Tell us about it, Professor.  We are very much mystified?” said the Pony Riders.

“A long time ago I remember to have read, somewhere, of a certain grass in this region that possessed peculiar narcotic properties—­”

“What’s narcotic?” interrupted Stacy.

“Something that makes you go to sleep when you can’t,” explained Tad Butler, rather ambiguously.