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