How does Buck maintain some measure of pride in Chapter 1 of The Call of the Wild?

When the unsuspecting Buck is stolen from his owner and sold to become a sled dog, he is taken by surprise; nevertheless, despite his abuse, Buck maintains a sense of pride as he struggles against his captors.
After Buck is sold, he is thrown into a baggage car of a train. Stunned, he lies for a while as he knows the sensation of riding on a locomotive. But, after he recovers some, Buck feels "the unbridled anger of a kidnapped king." When a man reaches for Buck's throat, Buck's quickness takes him by surprise as the dog's jaws close upon the man's hand. Buck does not let go until "his senses were choked out of him once more." 
After he is subdued, Buck is shoved into a crate. The next day four more "tormentors" come for Buck, and they poke sticks at him:

...[h]e promptly assailed with his teeth till he realized that that was what they wanted.

After Buck arrives at the destination, and a man takes a hatchet and damages the crate enough for Buck to reach out, 

Straight at the man he launched his one hundred and forty pounds of fury, surcharged with the pent passion of two days and nights. 

But, just as he is in mid air, Buck is hit with the handle of the ax that has split his cage. Again and again Buck lunges and attacks, but he is struck down by the handle of the ax as Buck feels the swift weight of the handle.

A dozen times he charged, and as often the club broke the charge and smashed him down.

Again and again Buck leaps at his oppressor, but is met with the stick until he finally collapses.