Quote 67
Buck's first day on the Dyea beach was like a nightmare. Every hour was filled with shock and surprise. (2.1)
Buck’s suffering is made worse because he has never experienced such hardships before.
Quote 68
A chill wind was blowing that nipped him sharply and bit with especial venom into his wounded shoulder. He lay down on the snow and attempted to sleep, but the frost soon drove him shivering to his feet. Miserable and disconsolate, he wandered about among the many tents, only to find that one place was as cold as another. (2.9)
The freezing cold of the North takes a toll on Buck, who is not used such weather.
Quote 69
Buck made his hole in the snow and slept the sleep of the exhausted just, but all too early was routed out in the cold darkness and harnessed with his mates to the sled. (2.18)
Fatigue plays an important role in the hardship Buck suffers.