In the first chapter of the novel, Buck's appearance and weight are described. At the beginning of the story, the narrator mentions that Buck weighs one hundred and forty pounds. Buck's father was a St. Bernard and his mother was a Scotch shepherd dog. Buck enjoyed his revered status on Judge Miller’s estate in the sun-kissed Santa Clara Valley, where he spent the first four years of his life swimming and running in the beautiful surrounding environment. Unfortunately, Buck is stolen and transported to the Northland, where he is forced to rely on his primitive instincts to survive the harsh, dangerous environment. There are times when Buck is driven to his physical limits by incompetent owners, and his weight dwindles down to one hundred and fifteen pounds. Fortunately, Buck is rescued by John Thorton, who nurses him back to health. He regains all of the weight he previously lost.