Call of the Wild

In Chapter Six, we learn that when John Thornton interfered in a bar fight between "Black" Burton and a tenderfoot, Buck nearly killed the instigator. When John fell into the rapids of a river, Buck aided Hans and Pete in rescuing him and breaking three ribs of his ribs. Later that winter in Dawson, Buck wins a $1600 bet for his master by pulling a sled loaded with a thousand pounds of flour.