What kind of life did Buck have with the Scotch half-breed?

Buck experienced hard work and regularity under the Scotch half-breed's whip.

It was no light running now, nor record time, but heavy toil each day, with a heavy load behind; for this was the mail train, carrying word from the world to the men who sought gold under the shadow of the Pole.

Buck did not like it, but he bore up well to the work, taking pride in it after the manner of Dave and Sol-leks, and seeing that his mates, whether they prided in it or not, did their fair share. It was a monotonous life, operating with machine-like regularity. One day was very like another.