In Chapter Three, Perrault and Francios discover what kind of a dog Buck really is. Initially, the think he will make a good sled dog based on spirit and body strength. However, his ferocity surprises them. At one point the assess that he is really 'devilish' because he keeps challenging the lead dogs superiority. Perraut says, "Dat dog two devils" and indicates that some day he is going to get Spitz the lead dog. This is in fact what happens. Additionally, they see in Buck a patient dog who was cunning. And they see a dog who although was bred as a domestic dog, he has the ability to revert to the primitive or wildness. They also see strength and endurance in him.
In Chapter Three, we see Buck get his bearings and become stronger. Initially he is worn out and unused to pulling a sled. His feet hurt and Francios makes little slippers for him to wear. By the end of the chapter, he has fulfilled Francios and Perrault's expectations and has beat out Spitz and become the primitive dog he indicated at the beginning of the chapter that he could be.