How does the man known as the Scotch half-breed treat the dogs in general and what do the dogs experience???

Francois and Perrault leave the team in the care of officials, a "Scotch half-breed," and pass out of Buck's life for good.

The work is now strict and heavy, as they are pulling the mail carts back over the trail to Dawson. Life is monotonous. Feeding time is the focus of each day. Buck quickly achieves mastery over the other dogs. He loves to sit in front of the fire and dream. Sometimes he dimly recalls memories from his California home. More often, he is visited by visions of an ancient life, his place with ancient humans. He sometimes thinks he sees a man, different from men today, and he remembers the rustle of beasts and the readiness for the fight.

They reach Dawson, and rather than the usual ten days of rest, they have another load of mail only two days later. The way is much harder this time, for it has begun to snow. The men are good to the dogs, feeding them before they eat themselves. The strength of the dogs is quickly waning. Dave becomes terribly ill, but refuses to stop pulling the sled. The driver puts Sol-lek in his place, meaning to allow him to run easily behind the sled. Dave cannot stand to see another dog doing his work. He runs into the soft snow beside Sol-lek, trying to resume his usual place, yelping in pain. Finally he falls behind the sled, but at the next stopping-place he once again attempts to resume his place. Finally the driver decides it is kinder to allow Dave to pull, for he will die either way. During his final pull, he often falls and is caught in the traces of the sled. The next morning, Dave is too weak to rise. The team is driven ahead some ways, but they cannot ignore the gunshot that rings out. Buck and everyone else know what the shot means.