“Drink,” begged the patient.

“Fetch him some water,” directed Professor Zepplin.

“No, no, no, señor,” protested Juan, gesticulating protestingly.

“What do you want?”

“Guess he wants something stronger than water,” suggested Ned.

“Si, si, si,” agreed the guide, showing his white teeth in an approving grin.

“You won’t get anything stronger than that in this outfit, unless you cook yourself some coffee,” muttered Tad.

“That’s what’s the matter with him,” decided Chunky, who had been observing the sick man keenly.

“Guess we drew a prize when we got Juan,” announced Walter.

“Give him some medicine, anyway,” urged Ned.  “He is sick—­ let him take the dose.”

“Let him have the worst you’ve got in your case, Professor,” added Tad, with a laugh.

A grim smile played about the corners of Professor Zepplin’s mouth as he ran his fingers over the bottles in his medicine case.  Finally, selecting one that seemed to fit the particular ailment of his patient, he directed Chunky to fetch a spoon.

By this time Juan was protesting volubly that he was “all better” and did not need the medicine.  The Professor gave no heed to the fellow’s protestations.

“Open your mouth,” he commanded.

Juan shut his teeth tightly together.

“Open your mouth!” commanded the Professor sternly.  “We want no sick men about this camp.  It will fix you in a minute.”

But the guide steadfastly refused to separate the white teeth.

“Boys, open his mouth while I pour the medicine down him,” gritted the Professor.

They required no urging to do the Professor’s bidding.  Tad and Ned ranged themselves on either side of the patient, while Chunky sat on the guide’s feet.  Almost before he was aware of their purpose the boys had pried his jaws open and into the opening thus made professor Zepplin dropped the concoction he had mixed.

The effect was electrical.  Juan leaped to his feet as if elevated by springs, uttering a yell that might have been heard a mile or more on the open plain.  But Juan did not run in a circle this time.  Acting upon the mathematical theory that a straight line is the shortest distance between two points, the guide made a break for the spring, howling like a madman.  The Pony Rider Boys looked on in amazement.

Juan fell on his knees before the spring, dipping up the water in his hands.

“What did you give him, professor?” grinned Tad.

“Hot drops!” answered the man of science tersely.

“Not that stuff you fed me when I ate too much honey in the Rockies?” questioned Stacy.

“The same.”

“Wow!  I had ten drops and it felt like a pailful when it got inside of me.”

“How much did you give Juan?” questioned Walter.

“Twenty drops,” answered Professor Zepplin without the suspicion of a smile on his face this time.