Leaping from their saddles, Nort and Dick hurried to the side of their cousin, chum and partner in the ranch venture. Eagerly they looked over his shoulder while he examined the strange object he had picked up, almost at the very door leading into the mysterious tunnel.

The instrument—for such it seemed to be—consisted of a shiny, nickeled part, which was what had reflected the moonlight, thus attracting Bud's attention to it. In addition there were two flexible tubes, of soft rubber, joining into one where they met the shiny metal.

The two tubes each terminated in hard rubber ends, pierced with a tiny hole, and on the end of the single tube was a bright metal disk. The whole formed a strange object, picked up as it was from the ground, and especially when the boy ranchers feared they had some cause for alarm.

"What in the world is it?" asked Bud, as he dangled it in front of his cousins. "I never saw anything like it before. Wait! I have it! Yellin' Kid said he was going to send to Kansas City for a flute he could play on. This must be part of it! He dropped it here; though that couldn't 'a' been him sneaking around the tunnel. But this is Yellin' Kid's musical instrument all right! Oh, won't I rag him, though! I wonder which end you blow in?"

"That isn't a musical instrument!" declared Nort, taking it from
Bud's hand.

"Not What is it then?" asked the western ranch lad.

"It's a stethoscope," declared Nort.

"Whew! x I didn't know Yellin' Kid could play one of them!" exclaimed Bud. "He must be more musical than any of us thought!"

"'Tisn't musical, I tell you!" cried Nort, half laughing. "This is a stethoscope—it's what a doctor listens to your lungs or heart with when you're sick."

"He never listened to mine!" boasted Bud, "at least not since I can remember, for I've never been sick."

"Well, I have," admitted Nort, "and so has Dick. You remember Dr. Thompson using one of these, don't you?" he asked his stout brother.

"Sure I do! And there's some other name for it besides plain stethoscope," declared Dick. "It's a long word—bi—di—"

"Binaural stethoscope! That's it!" broke in Nort. "I remember, now. I thought I'd never be able to say those words, but they come back to me now. Binaural stethoscope."

"'Tisn't good to eat, or shoot with, is it!" asked Bud, as he again took the instrument and turned it over and over in his hands.

"Eat! Shoot!" laughed Nort. "No, I tell you it's to listen to your heart beats, or lungs. Binaural means, simply, that it's fixed so you can listen with both ears at the same time. And stethoscope comes from two Greek words, stethos, the breast, and skopen, to view. It means, literally, to view inside the chest, but of course the doctors who use the stethoscope don't really do that. They only listen through the ear pieces—these," and he held up the two rubber tubes ending in hard nipples, pierced with small holes.

"What's the other end for!" asked Bud, indicating the shiny disk of metal that dangled from the single tube.

"That's the part the doctor holds on your chest or over your heart," Dick answered. "Sometimes the doctor puts it to your back to listen to your breathing from that side."

"Well, who in the world would have a—a binaural stethoscope out here!" asked Bud. "Yon reckon Doc. Tunison dropped it!" he went on, referring to the local veterinarian. "Shucks no! Cow doctors don't use 'em, not that I ever heard of," declared Nort. "Though Doc. Tunison is up to date."

"He sure was in discovering that it was germs which caused the epidemic outbreak in our stock last year," remarked Bud.

"Yes, we got out of that mighty lucky," chimed in Dick. "What's become of Pocut Pete?" he asked, referring to a scoundrel of a cowboy.

"Oh, Del Pinzo and Hank Fisher had pull enough to get him out of jail, after he'd served only part of his term for infecting our stock," said Bud. He had reference to something which is explained in the volume immediately preceding this. Del Pinzo was a notorious Mexican half-breed who, more than once, had made trouble for the boy ranchers. Hank Fisher was the owner of Double Z ranch, adjoining that of Square M, one of Mr. Merkel's, and also adjoining Happy Valley. Pocut Pete was believed to be a tool of these two unscrupulous men, and Del Pinzo had at his command Several Greasers who slipped back and forth over the Mexican border, not far from which were located the holdings of Mr. Merkel and the boy ranchers.

"Well, this is a stethoscope all right," went on Nort, as Bud turned toward his pony, with the evident intention of mounting.

"And I'd give a lot to know what it's doing here, and who dropped it," spoke Bud. "Let's look around a little more. I'm not at all satisfied with this. I sure saw, some one here, and this proves it," and he stuffed the doctor's instrument into his pocket.

"It doesn't prove that the man you saw—or thought you just saw—sneaking around here dropped it," spoke Nort. "We've been away for a week, and it may have been dropped any day within that time."

"Yes," agreed Bud. "But who was monkeying around here as we rode back to camp? That's what I want to know!"

However, search as the boy ranchers did, they found no midnight visitor. All was quiet at their camp, save for the distant howl of a coyote, and the splash of the water into the reservoir. All the stock had been driven away from Happy Valley to the big round-up at Diamond X, but soon the fertile glade would again be dotted with hungry cattle.

"Well, I reckon we'll have to give up," said Bud, when a thorough search had been made, and no one discovered.

"The tunnel door doesn't show any signs of an attempt having been made to bust it; does it?" asked Dick.

"Not as far as I can see, in this light," Bud replied. "We'll take a stroll up here in the morning," he went on as he thrust the stethoscope into his pocket. "Now for a little grub, and then to hit the hay. Oh, boy! But I to tired!"

So were the others, and after rummaging among their camp stores, and eating some crackers and canned peaches, the boys, having picketed their horses, turned in, rolled up in their blankets, and were asleep almost as soon as their heads were on the pillows, which were, as a matter of fact, stuffed with hay.

An examination, next morning, disclosed nothing more in the neighborhood of the tunnel entrance than their own and, their ponies' feet marks, until Bud, with an exclamation, pointed to several cigarette stubs on the ground, and a number of half-burned matches.

"Some one was here last night—or yesterday!" he declared. "And they stood in this one spot for some time—either resting or spying."

"What would they be spying on!" asked Dick.

"Search me!" frankly admitted Bud. "But since we had that water fight I'm suspicious of everything. Those cigarette stubs are fresh, and were dropped last night, or yesterday. None of us use 'em, and though some of our cow punchers do they haven't been here lately enough to have left this fresh evidence. The stubs are new ones."

"Well, maybe there was some one here last night," said Dick.

"I'm positive of it!" declared Bud. "Let's take another look at the big door lock."

Even a close inspection, however, failed to disclose any signs of the great portal, or its heavy padlock having been tampered with. Nor were there any marks tending to show where an effort had been made to force boards off the frame in which the door was set.

"Well, we'll just have to wait," said Bud, as he turned to go back down to the tents. "Hello," he suddenly added, as he gazed off up the valley. "Here comes somebody, riding like all possessed, too!"

The boy ranchers watched the approach of the solitary horseman, and, as he drew nearer Bud exclaimed:

"It's Buck Tooth!"

It was, in fact, that same Zuni Indian, who had been engaged as a sort of camp cook and ranch hand by Bud's father, later being transferred to Bud's service. Buck Tooth was devoted to the boy ranchers.

"What's matter, Buck! What for you ride so pronto fashion!" asked Bud as the Indian, a superb horseman, drew rein close to the boy ranchers. "You race, maybe, Buck Tooth!"

"Yep—race tell you bad news!" half-grunted the Zuni.

"Bad news!" faltered Bud. "Is it my mother—dad—-"

"Them all well," said Buck Tooth. "But got bad news all same. You see anybody out here?" and he slipped from his saddle to rest his almost winded steed.