Three dogs could not drag the sled so fast nor for so long hours as could six, and they were showing unmistakable signs of playing out.

And the men went early to bed, Bill first seeing to it that the dogs were tied out of gnawing-reach of one another.
But the wolves were growing bolder, and the men were aroused more than once from their sleep.

So near did the wolves approach, that the dogs became frantic with terror, and it was necessary to replenish the fire from time to time in order to keep the adventurous marauders at safer distance.
"I've hearn sailors talk of sharks followin' a ship," Bill remarked, as he crawled back into the blankets after one such replenishing of the fire.

"Well, them wolves is land sharks.

They know their business better'n we do, an' they ain't a-holdin' our trail this way for their health.