In this chapter, Buck will be characterized as an animal of great love, loyalty, and devotion; he will become completely devoted to John Thornton, who is, in contrast to Hal and Charles, Buck's other masters, characterized as being the ideal "master." Not since Buck's days with Judge Miller has Buck experienced "love, genuine passionate love." Even in the Santa Clara Valley, with the Judge's son, Buck's relationship had been one of a "working partnership" and a sort of "pompous guardianship," and even his relationship with the Judge had been a "stately and dignified friendship." However, London now writes that the love which Buck feels for John Thornton has quickly developed into a feverish and burning admiration. Furthermore, in contrast to the events in the last chapter, where dog and man could not work together at all, here in Chapter 6, we are shown the great heights to which a dog can rise if he is inspired by love and admiration for his master. Certainly at the beginning of this chapter, he is as close to death as is physically possible, and, accordingly, Thornton devotes considerable time and patience while he is nursing Buck back to health.
As this chapter begins, we learn a bit of the history about John Thornton and how he came to be camped next to the river. The previous winter, Thornton had frozen his feet, and his partners had left him behind to recover. During both Buck's and Thornton's recoveries, there are two other of Thornton's dogs, Skeet and Nig, who are very friendly towards Buck, who is surprised; he expected them to show some signs of jealousy. Yet, unlike the other two dogs, Buck does not force Thornton's attention upon him; Buck is content to lie at a distance, watching Thornton with love and admiration. In fact, for a long time after Thornton rescues Buck, Buck is uncomfortable when Thornton is out of his sight, because Buck remembers how people like Perrault and François, and even the Scotch half-breed — all good masters — had, one day, suddenly disappeared, leaving Buck finally at the mercy of Hal, Charles, and Mercedes.
London, however, does not suddenly make Buck into an all-good, ideal, one-dimensional dog. He says that in spite of the great love which Buck has for John Thornton, Buck still retains a strong sense of the primitive. In other words, Buck's faithfulness and devotion — qualities associated with a civilized society — are apparent in his conduct toward John Thornton, but Buck still retains his protective instincts for the wild and his mastery of the primitive.
London also reminds us that Buck's body is scarred, "scored by the teeth of many dogs," so much so that other dogs would quickly acknowledge his supremacy in a fight. Buck had indeed "learned well the law of club and fang . . . he must master . . . because to show mercy was a weakness. Mercy did not exist in the primordial life . . . kill or be killed, eat or be eaten was the law." During these times, Buck relishes living with John Thornton, yet there are other, deeper claims to him also. From far deep down in the forest, he often hears wild sounds and calls that are mysteriously thrilling and compelling. He often ponders the nature of these mysterious calls, and he often thinks of running toward them, except for the fact that "the love of John Thornton drew him back to the fire again." When Thornton's partners, Hans and Pete, arrive with the long-awaited raft, Buck refuses to acknowledge them, except as friends of Thornton. He feels loyalty only to Thornton.
At this point, London shifts his point of view from Buck to the character of John Thornton, and we discover that during their dual recuperation, Thornton develops a great admiration for Buck. One day, therefore, after Hans and Pete's arrival, Thornton and his friends are sitting on the edge of a chasm, into which Thornton suddenly orders Buck to jump. Evidently, Thornton does this in order to demonstrate to Hans and Pete that Buck is totally devoted to him. In London's words, "The next instant he [Thorton] was grappling with Buck on the extreme edge."
Later on, in Circle City, Buck has yet another opportunity to demonstrate his devotion to John Thornton. An evil-tempered and malicious man named "Black" Burton is bullying a young "tenderfoot" in a bar (a tenderfoot is an inexperienced person in the frontier). When John Thornton tries to prevent a nasty fight, Burton strikes Thornton solidly and sends him sprawling. Immediately, Buck attacks the man, and even though Burton is able to protect himself from two different lunges by the dog, Buck is finally able to tear open the man's throat. A meeting is immediately called, and it is decided that Buck had sufficient provocation for defending his master against violence. Later on that year, Buck again proves his worth by again saving Thornton's life. While attempting to maneuver some dangerous rapids, Thornton's boat overturns, flinging him into the cold, swirling water, which, in turn, sweeps him into the midst of such wild rapids that not even a strong swimmer could survive. Buck does not hesitate to act; he swims out to Thornton, who knows that they are not strong enough to conquer the turbulent rapids. Thus he orders Buck back to the shore, and even though Buck hates to desert his master, he nevertheless obeys Thornton's commands. Once on shore, Hans and Pete tie a long rope to Buck's collar and send him back into the water with it. Buck launches boldly out into the stream, but finds that he cannot travel straight enough, and he misses Thornton by only a few yards. Again, he returns to shore, where the rope is once again attached to him. "He had miscalculated once, but he would not be guilty of it a second time." This time, he reaches Thornton, who is able to grab the rope, and almost "strangling and suffocating," the man and the dog, both bruised and battered, are dragged back to the shore. There, they discover that Buck has two broken ribs, and Thornton announces that they will not break camp until Buck's ribs are fully healed.
A third episode concerning Buck's extraordinary character occurs sometime later, and it is such a feat that Buck's fame spreads throughout all Alaska. It begins in a saloon, where some men are boasting of the exploits of their dogs. Thornton is intrigued and is driven to maintain that Buck can pull a sled with a thousand pounds on it. Furthermore, he says, Buck can break the sled loose — even if it is frozen fast — and, furthermore, that he can pull it a hundred yards. A man named Matthewson bets Thornton that Buck cannot do such an incredible feat; in fact, he is willing to bet a thousand dollars that Buck cannot do it. Thornton, at this point, momentarily becomes unsure whether or not Buck can actually perform such an enormous and appalling task, and he is confused as to what to do, since neither he, nor Hans, nor Pete has a thousand dollars. At that moment, however, an old friend of Thornton's, Jim O'Brien, walks into the saloon and offers to lend Thornton a thousand dollars. The bet is on, and all of the occupants of the town pour into the streets, the men all placing great odds that Buck cannot budge the sled. When it is discovered that the sled's runners are, in fact, frozen to the ice, and Thornton is not able to break the sled loose, the odds soar tremendously. Matthewson, however, offers to increase his wager by another thousand — at three to one odds — but Thornton, Hans and Pete are able to raise only two hundred dollars, which they bet against Matthewson's six hundred.
As the contest is about to begin, John Thornton kneels beside Buck's head, whispering quiet statements of endearment: "As you love me, Buck. As you love me." Buck answers this plea by taking "his master's mittened hands between his jaws, pressing in with his teeth . . . it was the answer, in terms, not of speech, but of love." Thornton orders the dog to "MUSH," and so Buck, mustering every last bit of strength he has, every muscle and sinew straining under the tremendous weight, heaves forward. But one of Buck's feet slips, and he suddenly falls down in the snow. Yet, because of his amazing resiliency, he stands up and pulls even harder, and finally he is able to move the sled — inch by inch, foot by foot — until he finally covers the hundred yards previously marked off as being the finish line. The crowd cheers, and in appreciation, Thornton kneels by the dog. The famed "King of Skookum Bench" offers to pay Thornton a thousand dollars for Buck, but Thornton rejects the offer.
Here in this chapter, then, just before Buck will return to the primitive world, London shows us the love, the devotion, the affection, and the cooperation that can exist between a man and a dog. Under certain circumstances, especially after a man has saved a dog's life, the dog can be expected to save his master's reputation.