Quote 1
John Thornton asked little of man or nature. He was unafraid of the wild. With a handful of salt and a rifle he could plunge into the wilderness and fare wherever he pleased and as long as he pleased. Being in no haste, Indian fashion, he hunted his dinner in the course of the day's travel; and if he failed to find it, like the Indian, he kept on traveling, secure in the knowledge that sooner or later he would come to it. So, on this great journey into the East, straight meat was the bill of fare, ammunition and tools principally made up the load on the sled, and the time-card was drawn upon the limitless future. (7.3)
Like Buck, Thornton learns to work with nature to survive in it.
"You poor devil," said John Thornton, and Buck licked his hand. (5.66)
Buck’s feelings for Thornton are immediate.
He had a way of taking Buck's head roughly between his hands, and resting his own head upon Buck's, of shaking him back and forth, the while calling him ill names that to Buck were love names. Buck knew no greater joy than that rough embrace and the sound of murmured oaths, and at each jerk back and forth it seemed that his heart would be shaken out of his body so great was its ecstasy. And when, released, he sprang to his feet, his mouth laughing, his eyes eloquent, his throat vibrant with unuttered sound, and in that fashion remained without movement, John Thornton would reverently exclaim, "God! you can all but speak!" (6.4)
London uses the word "ecstasy" both to describe Buck’s emotion at killing a rabbit and his feelings with Thornton. This suggests a connection between the extremes of love and death.
Quote 4
For Thornton, however, his love seemed to grow and grow. He, alone among men, could put a pack upon Buck's back in the summer traveling. Nothing was too great for Buck to do, when Thornton commanded. One day (they had grub-staked themselves from the proceeds of the raft and left Dawson for the head-waters of the Tanana) the men and dogs were sitting on the crest of a cliff which fell away, straight down, to naked bed-rock three hundred feet below. John Thornton was sitting near the edge, Buck at his shoulder. A thoughtless whim seized Thornton, and he drew the attention of Hans and Pete to the experiment he had in mind. "Jump, Buck!" he commanded, sweeping his arm out and over the chasm. The next instant he was grappling with Buck on the extreme edge, while Hans and Pete were dragging them back into safety. (6.13)
Buck’s loyalty to Thornton is blind—such emotion is dangerous, and its threat to Buck’s life is counter to the survival—given laws he learned in the North.
Quote 5
Thornton knelt down by Buck's side. He took his head in his two hands and rested cheek on cheek. He did not playfully shake him, as was his wont, or murmur soft love curses; but he whispered in his ear. "As you love me, Buck. As you love me," was what he whispered. Buck whined with suppressed eagerness. (6.48)
Buck’s emotional love for Thornton overcomes physical tests.
Quote 6
The crowd was watching curiously. The affair was growing mysterious. It seemed like a conjuration. As Thornton got to his feet, Buck seized his mittened hand between his jaws, pressing in with his teeth and releasing slowly, half-reluctantly. It was the answer, in terms, not of speech, but of love. Thornton stepped well back. (6.49)
Again we see a connection between love and violence, as Buck uses a physical act to express his emotions.
Quote 7
But Thornton fell on his knees beside Buck. Head was against head, and he was shaking him back and forth. Those who hurried up heard him cursing Buck, and he cursed him long and fervently, and softly and lovingly. (6.59)
While Buck bites Thornton to show his love, Thornton curses him. There is a painful aspect to their love.
Quote 8
John Thornton was eating dinner when Buck dashed into camp and sprang upon him in a frenzy of affection, overturning him, scrambling upon him, licking his face, biting his hand--"playing the general tom-fool," as John Thornton characterized it, the while he shook Buck back and forth and cursed him lovingly. (7.18)
Although Buck’s loyalty to Thornton may waver for moments in the wild, he never loses his devotion.
Quote 9
"Never was there such a dog," said John Thornton one day, as the partners watched Buck marching out of camp. (7.23)
Thornton recognizes Buck’s true value.
Quote 10
"And they told you true," John Thornton answered. "The bottom's likely to drop out at any moment. Only fools, with the blind luck of fools, could have made it. I tell you straight, I wouldn't risk my carcass on that ice for all the gold in Alaska." (5.54)
Some wiser men are attuned to inevitable events.