Quote 16
Sometimes as he crouched there, blinking dreamily at the flames, it seemed that the flames were of another fire, and that as he crouched by this other fire he saw another and different man from the half-breed cook before him. This other man was shorter of leg and longer of arm, with muscles that were stringy and knotty rather than rounded and swelling. The hair of this man was long and matted, and his head slanted back under it from the eyes. He uttered strange sounds, and seemed very much afraid of the darkness, into which he peered continually, clutching in his hand, which hung midway between knee and foot, a stick with a heavy stone made fast to the end. He was all but naked, a ragged and fire-scorched skin hanging part way down his back, but on his body there was much hair. In some places, across the chest and shoulders and down the outside of the arms and thighs, it was matted into almost a thick fur. He did not stand erect, but with trunk inclined forward from the hips, on legs that bent at the knees. About his body there was a peculiar springiness, or resiliency, almost catlike, and a quick alertness as of one who lived in perpetual fear of things seen and unseen. (4.24)
Buck’s relationship with man takes many different forms. He feels a unique kinship to the man by the fire in his dreams that is different from anything he experiences in reality. Buck later reveals that this kinship has to do with fear.
Quote 17
At other times this hairy man squatted by the fire with head between his legs and slept. On such occasions his elbows were on his knees, his hands clasped above his head as though to shed rain by the hairy arms. And beyond that fire, in the circling darkness, Buck could see many gleaming coals, two by two, always two by two, which he knew to be the eyes of great beasts of prey. And he could hear the crashing of their bodies through the undergrowth, and the noises they made in the night. And dreaming there by the Yukon bank, with lazy eyes blinking at the fire, these sounds and sights of another world would make the hair to rise along his back and stand on end across his shoulders and up his neck, till he whimpered low and suppressedly, or growled softly, and the half-breed cook shouted at him, "Hey, you Buck, wake up!" Whereupon the other world would vanish and the real world come into his eyes, and he would get up and yawn and stretch as though he had been asleep. (4.25)
Buck gets more involved with this other dream-world as his transformation progresses and as he becomes more in tune with his primitive side.
Quote 18
Faithfulness and devotion, things born of fire and roof, were his; yet he retained his wildness and wiliness. He was a thing of the wild, come in from the wild to sit by John Thornton's fire, rather than a dog of the soft Southland stamped with the marks of generations of civilization. (6.8)
By the time he meets Thornton, Buck is already irrevocably changed from the dog he was when the story began.