"Tatanka! Tatanka! The buffaloes! The buffaloes!" cried the sentinels who had been watching on the north side of the camp.

Then the Sioux suddenly realized the truth. A vast herd of stampeded buffaloes were thundering down upon them. There was not a moment to spare. Springing upon the frightened ponies, the Sioux rode madly into the night to escape from the great mass of panic-stricken beasts behind them. The buffaloes were sweeping across the plain with the irresistible force of an avalanche, and the horsemen knew that only the speed of their ponies could save them. They kept close together, and rode at a breakneck pace. A false step meant destruction for horse and rider, and the Sioux made little attempt to guide the agile little beasts beneath them.

Sun Bird and White Otter soon found themselves beside one another at the head of the company. The two ponies were running evenly, and it was apparent that neither of them had reached the limit of its speed. Nevertheless, they were well in advance of all the other ponies, and appeared to be increasing their lead with each stride.

"That wild horse can run," laughed Sun Bird as his blood tingled with the excitement of the race. "Come, we will see what that pony can do."

"Hi!" shouted White Otter, as Sun Bird suddenly took the lead.

He had carefully estimated the ability of the little roan which Sun Bird rode, and felt sure that it was a worthy competitor for the piebald. Now, as Sun Bird applied his rawhide quirt, the roan began to show its speed. The piebald, however, quickly accepted the challenge, and although White Otter made no effort to force it the fiery little beast was soon at the shoulder of the roan. Then they raced madly through the darkness at a speed which few if any of the ponies in the great Dacotah nation could equal. Sun Bird was leaning forward and vigorously applying his whip. White Otter, however, was still allowing the piebald to make its own pace. Inch by inch it crept steadily forward until the roan's lead was cut to a nose length. Then, as he perceived that the roan had reached the limit of its powers, White Otter pulled heavily against the lower jaw of the piebald. He knew that a few more strides would take it into the lead, and regard for the pride of his friend made him unwilling to claim the victory.

"Listen," he cried, suddenly. "Our people have turned around. Come, we must follow them."

"No! No! I see what you are trying to do," Sun Bird cried, impatiently. "Come, let me see that pony run."

Then the Minneconjoux struck the piebald a sharp blow with his quirt, and the marvelous beast bounded past him and raced away at a speed which astounded its rider. White Otter could scarcely believe that he was mounted upon a creature of real flesh and blood, for the piebald was rushing through the night at a pace which seemed beyond the powers of anything mortal. Carried away with enthusiasm, the Ogalala applied his quirt for the first time, and the piebald reached the limit of its speed. White Otter was forced to crouch close over the pony's neck to keep his breath. He was dazed by the pace at which he was being carried across the plain. It seemed as if he were flying through space on the wings of a tempest.

"It must be a Medicine Horse," he whispered, superstitiously.