His development (or retrogression) was rapid. His muscles became hard as iron, and he grew callous to all ordinary pain. He achieved an internal as well as external economy. He could eat anything, no matter how loathsome or indigestible; and, once eaten, the juices of his stomach extracted the last least particle of nutriment; and his blood carried it to the farthest reaches of his body, building it into the toughest and stoutest of tissues. Sight and scent became remarkably keen, while his hearing developed such acuteness that in his sleep he heard the faintest sound and knew whether it heralded peace or peril. He learned to bite the ice out with his teeth when it collected between his toes; and when he was thirsty and there was a thick scum of ice over the water hole, he would break it by rearing and striking it with stiff fore legs. His most conspicuous trait was an ability to scent the wind and forecast it a night in advance. No matter how breathless the air when he dug his nest by tree or bank, the wind that later blew inevitably found him to leeward, sheltered and snug.

And not only did he learn by experience, but instincts long dead became alive again. The domesticated generations fell from him. In vague ways he remembered back to the youth of the breed, to the time the wild dogs ranged in packs through the primeval forest and killed their meat as they ran it down. It was no task for him to learn to fight with cut and slash and the quick wolf snap. In this manner had fought forgotten ancestors. They quickened the old life within him, and the old tricks which they had stamped into the heredity of the breed were his tricks. They came to him without effort or discovery, as though they had been his always. And when, on the still cold nights, he pointed his nose at a star and howled long and wolflike, it was his ancestors, dead and dust, pointing nose at star and howling down through the centuries and through him. And his cadences were their cadences, the cadences which voiced their woe and what to them was the meaning of the stiffness, and the cold, and dark.

Thus, as token of what a puppet thing life is, the ancient song surged through him and he came into his own again; and he came because men had found a yellow metal in the North, and because Manuel was a gardener's helper whose wages did not lap over the needs of his wife and divers small copies of himself.

At the Pelly one morning, as they were harnessing up, Dolly, who had never been conspicuous for anything, went suddenly mad. She announced her condition by a long, heartbreaking wolf howl that sent every dog bristling with fear, then sprang straight for Buck. He had never seen a dog go mad, nor did he have any reason to fear madness; yet he knew that here was horror, and fled away from it in a panic. Straight away he raced, with Dolly, panting and frothing, one leap behind; nor could she gain on him, so great was his terror, nor could he leave her, so great was her madness. He plunged through the wooded breast of the island, flew down to the lower end, crossed a back channel filled with rough ice to another island, gained a third island, curved back to the main river, and in desperation started to cross it. And all the time, though he did not look, he could hear her snarling just one leap behind. Francois called to him a quarter of a mile away and he doubled back, still one leap ahead, gasping painfully for air and putting all his faith in that Francois would save him. The dog–driver held the axe poised in his hand, and as Buck shot past him the axe crashed down upon mad Dolly's head.

Buck staggered over against the sled, exhausted, sobbing for breath, helpless. This was Spitz's opportunity. He sprang upon Buck, and twice his teeth sank into his unresisting foe and ripped and tore the flesh to the bone. Then Francois's lash descended, and Buck had the satisfaction of watching Spitz receive the worst whipping as yet administered to any of the teams.

"One devil, dat Spitz," remarked Perrault. "Some dam day heem keel dat Buck."

"Dat Buck two devils," was Francois's rejoinder. "All de tam I watch dat Buck I know for sure. Lissen: some dam fine day heem get mad lak hell an' den heem chew dat Spitz all up an' spit heem out on de snow. Sure. I know."

It was beautiful spring weather, but neither dogs nor humans were aware of it. Each day the sun rose earlier and set later. It was dawn by three in the morning, and twilight lingered till nine at night. The whole long day was a blaze of sunshine. The ghostly winter silence had given way to the great spring murmur of awakening life. This murmur arose from all the land, fraught with the joy of living. It came from the things that lived and moved again, things which had been as dead and which had not moved during the long months of frost. The sap was rising in the pines. The willows and aspens were bursting out in young buds. Shrubs and vines were putting on fresh garbs of green. Crickets sang in the nights, and in the days all manner of creeping, crawling things rustled forth into the sun. Partridges and woodpeckers were booming and knocking in the forest. Squirrels were chattering, birds singing, and overhead honked the wild–fowl driving up from the south in cunning wedges that split the air.

From every hill slope came the trickle of running water, the music of unseen fountains. All things were thawing, bending, snapping. The Yukon was straining to break loose the ice that bound it down. It ate away from beneath; the sun ate from above. Air–holes formed, fissures sprang and spread apart, while thin sections of ice fell through bodily into the river. And amid all this bursting, rending, throbbing of awakening life, under the blazing sun and through the soft–sighing breezes, like wayfarers to death, staggered the two men, the woman, and the huskies.

With the dogs falling, Mercedes weeping and riding, Hal swearing innocuously, and Charles's eyes wistfully watering, they staggered into John Thornton's camp at the mouth of White River. When they halted, the dogs dropped down as though they had all been struck dead. Mercedes dried her eyes and looked at John Thornton. Charles sat down on a log to rest. He sat down very slowly and painstakingly what of his great stiffness. Hal did the talking. John Thornton was whittling the last touches on an axe–handle he had made from a stick of birch. He whittled and listened, gave monosyllabic replies, and, when it was asked, terse advice. He knew the breed, and he gave his advice in the certainty that it would not be followed.

He was older than the days he had seen and the breaths he had drawn. He linked the past with the present, and the eternity behind him throbbed through him in a mighty rhythm to which he swayed as the tides and seasons swayed. He sat by John Thornton's fire, a broad–breasted dog, white–fanged and long–furred; but behind him were the shades of all manner of dogs, half–wolves and wild wolves, urgent and prompting, tasting the savor of the meat he ate, thirsting for the water he drank, scenting the wind with him, listening with him and telling him the sounds made by the wild life in the forest, dictating his moods, directing his actions, lying down to sleep with him when he lay down, and dreaming with him and beyond him and becoming themselves the stuff of his dreams.

So peremptorily did these shades beckon him, that each day mankind and the claims of mankind slipped farther from him. Deep in the forest a call was sounding, and as often as he heard this call, mysteriously thrilling and luring, he felt compelled to turn his back upon the fire and the beaten earth around it, and to plunge into the forest, and on and on, he knew not where or why; nor did he wonder where or why, the call sounding imperiously, deep in the forest. But as often as he gained the soft unbroken earth and the green shade, the love for John Thornton drew him back to the fire again.

Thornton alone held him. The rest of mankind was as nothing. Chance travellers might praise or pet him; but he was cold under it all, and from a too demonstrative man he would get up and walk away. When Thornton's partners, Hans and Pete, arrived on the long–expected raft, Buck refused to notice them till he learned they were close to Thornton; after that he tolerated them in a passive sort of way, accepting favors from them as though he favored them by accepting. They were of the same large type as Thornton, living close to the earth, thinking simply and seeing clearly; and ere they swung the raft into the big eddy by the saw–mill at Dawson, they understood Buck and his ways, and did not insist upon an intimacy such as obtained with Skeet and Nig.

As twilight fell the old bull stood with lowered head, watching his mates–the cows he had known, the calves he had fathered, the bulls he had mastered–as they shambled on at a rapid pace through the fading light. He could not follow, for before his nose leaped the merciless fanged terror that would not let him go. Three hundredweight more than half a ton he weighed; he had lived a long, strong life, full of fight and struggle, and at the end he faced death at the teeth of a creature whose head did not reach beyond his great knuckled knees.

From then on, night and day, Buck never left his prey, never gave it a moment's rest, never permitted it to browse the leaves of trees or the shoots of young birch and willow. Nor did he give the wounded bull opportunity to slake his burning thirst in the slender trickling streams they crossed. Often, in desperation, he burst into long stretches of flight. At such times Buck did not attempt to stay him, but loped easily at his heels, satisfied with the way the game was played, lying down when the moose stood still, attacking him fiercely when he strove to eat or drink.

The great head drooped more and more under its tree of horns, and the shambling trot grew weak and weaker. He took to standing for long periods, with nose to the ground and dejected ears dropped limply; and Buck found more time in which to get water for himself and in which to rest. At such moments, panting with red lolling tongue and with eyes fixed upon the big bull, it appeared to Buck that a change was coming over the face of things. He could feel a new stir in the land. As the moose were coming into the land, other kinds of life were coming in. Forest and stream and air seemed palpitant with their presence. The news of it was borne in upon him, not by sight, or sound, or smell, but by some other and subtler sense. He heard nothing, saw nothing, yet knew that the land was somehow different; that through it strange things were afoot and ranging; and he resolved to investigate after he had finished the business in hand.