Buck slowly gets his strength back. John Thornton, it turns out, had frozen his feet during the previous winter, and he and his dogs are now waiting for the river to melt and for a raft to take them down to Dawson. With Thornton, Buck experiences love for the first time, developing a strong affection for the man who saved his life and who proves an ideal master. Thornton treats his dogs as if they are his own children, and Buck responds with adoration and obeys all commands. Once, to test Buck, Thornton tells him to jump off a cliff; Buck begins to obey before Thornton stops him.

Even though Buck is happy with Thornton, his wild instincts still remain strong, and he fights as fiercely as ever. Now, however, he fights in defense of Thornton. In Dawson, Thornton steps in to stop a fight in a bar, and one of the combatants lashes out at him. Immediately, Buck hurls himself at the man’s throat; the man narrowly escapes having his throat ripped open when he throws up his hand, though Buck succeeds in partially ripping it open with his second try. A meeting is called on the spot to decide what to do with Buck, and the miners rule that his aggressive behavior was justified, since he acted in defense of Thornton. Soon, Buck has earned a reputation throughout Alaska for loyalty and fercocity.

Buck saves Thornton’s life again when Thornton is thrown out of a boat and gets caught in fierce rapids. Buck swims to the slick rock where Thornton clings for his life, and the other men attach a rope to Buck’s neck and shoulders. After several failed attempts, Thornton grabs onto his neck, and the two are pulled back to safety.

That winter, on a strange whim, Thornton boasts that Buck can start a sled with a thousand pounds loaded on it. Other men challenge his claim, betting that Buck cannot perform that task before their eyes. A man named Matthewson, who has grown rich in the gold rush, bets a thousand dollars that Buck cannot pull his sled—which is outside, loaded with a thousand pounds of flour. Thornton himself doubts it, but he makes the bet anyway, borrowing the money from a friend to cover the wager. Several hundred men come to watch, giving odds—first two to one, then three to one when the terms of the bet are clarified—that Buck cannot break out the sled, and a confident Matthewson throws on another $600 at those odds. Once Buck is harnessed in, he first breaks the sled free of the ice, then pulls it a hundred yards. The crowd of men cheers in amazement, with even Matthewson joining in the applause.

For the time being, Buck’s slowly developing identity as a wild animal is quelled by his new devotion to John Thornton and, through him, to the man-dog relationship. If the terrible trio of Hal, Charles, and Mercedes comprises the worst master possible for an animal, then Thornton may be the best. His relationship with Buck is founded on mutual protection and affection—he saves Buck’s life, and then Buck not only does the same for him, but also bears out Thornton’s faith in him by winning a seemingly impossible wager. This is the first time, London emphasizes, that Buck has actually felt love for a human being—perhaps because it is the first time that he is neither a pampered pet nor a drudge, toiling away to pull a sled. Whatever the cause, this love is presented as being profoundly physi-cal—Thornton shakes him and wrestles with him, and Buck has a way of biting his master’s hand that, without drawing blood, is strong enough to leave the marks of his teeth in Thornton’s flesh.

Thornton’s relationship to Buck seems to be the fulfillment of Buck’s mystical vision of primitive man, a vision that recurs in Chapter VII. The relationship of man to dog, the novel suggests, is not a creation of civilization—rather, it is a much more primal bond that can survive even in a dog like Buck, whose civilized veneer is almost entirely scraped away to expose the wild animal beneath. Buck is no longer a pet or a slave, but he still has a master. He has not yet become an animal of the wild.

London also uses this chapter to set the stage for Buck’s eventual break with the world of men by telling us that this love for Thornton is the only thing that keeps Buck from going wild. Buck remains merciless, for one thing, holding on to the lessons that he learned from Curly’s death and from his war with Spitz—namely, that “he must master or be mastered.” His love for Thornton coexists with his knowledge that “kill or be killed, eat or be eaten, was the law.” His ability to still feel love is significant and suggests that London is not content with the bleakness of a Darwinian cosmos or with the pure cruelty and struggle for mastery of a Nietzschean worldview. But while Buck’s love is strong, it is for Thornton alone and not for mankind in general; he has learned well, especially from Hal and Charles, that mankind at large does not deserve his love. “Thornton alone held him,” London writes, and then describes how Buck ranges away from the fire and senses a “call” beckoning him into the deep forests and wilderness. For the time being, Buck resists this call for Thornton’s sake, but we are left to wonder what will happen if and when he and Thornton separate. Thus, Buck stands poised on the brink of a final break with the world of men, and the stage is set for the developments of the final chapter.