White Fang senses change in the air. Matt believes that White Fang has caught on to Scott's plan to leave the Klondike. Scott insists that he can't take a "wolf" with him to California and entrusts him to Matt's care.
Scott believes he can't take White Fang to California, because White Fang is too wild for society. That Scott calls White Fang a "wolf," and not a dog, emphasizes his feral nature.
When White Fang sees his master's bags packed, he howls throughout the night, just as he did over the empty Indian camp. The next morning, Scott loads his bags onto the sled, says goodbye to White Fang, and locks him up in the cabin so that White Fang won't follow him on the "long trail."
White Fang's howl represents his deep attachment to his master. Just as White Fang howled because he missed man's companionship at the Indian camp, he howls now because he will miss Scott.
Scott is about to board the steamboat when White Fang appears on deck. Scott notices that there are cuts on his muzzle. Matt realizes that White Fang broke through the cabin's window to follow his master. Scott tells Matt he needn't write to him about White Fang, because he's taking the wolf with him to California.
White Fang shows his deep devotion to Scott by breaking out of the cabin, despite the pain it must have caused him. No barrier can hold back his love for his master. With this show of devotion he convinces Scott that he will listen to his master in California—that because of his devotion he can be domesticated.