It is highly ironic that the discovery of the Pearl of the World as it is called in this text does not actually bring lasting joy and happiness to Kino and his family It only brings eternal misery, which explains Kino's decision to fling the pearl back into the sea. The effect of the pearl's discovery is clearly remarked on by the author of this slim but powerful novella:
The news stirred up something infinitely black and evil in the town; the black distillate was like the scorpion, or like the hunger in the smell of food, or like loneliness when love is withheld. The poison sacs of the town began to manufacture venom, and the town swelled and puffed with the pressure of it.
One character who immediately and incredibly hypocritically puts on a "mask" to cheat Kino is the Doctor. His hypocrisy is perhaps worse because, having refused to treat his son, he suddenly turns up at Kino's house, playing the role of caring doctor, even though Kino's son is better. He therefore lies to devise treatment that is necessary for the patient and by so doing gain some of the wealth from Kino. Even though Kino stands in the doorway as the Doctor comes, with "hatred raging and flaming in the back of his eyes" he remains frustrated by his lack of knowledge and his desire to protect his son. The Doctor therefore would be a very good character to select as a wearer of a "mask" to trick Kino.
The Doctor is racist and classist. He will not treat Coyotito because he is Indian (Native) and because he is poor. The Doctor essentially treats Kino, his family and the townspeople like animals. When Kino and Juana first approach the Doctor, he refuses to treat them, saying his profession is “not veterinary.”
When Kino obtains the beautiful pearl, the Doctor pretends to change his attitude. He goes so far as to visit Kino and calls him his client. The Doctor is actually just the same greedy racist he was before. He is wearing a mask of compassion in order to swindle Kino or just steal the pearl. He uses people to steal the pearl for him. So the Doctor’s attitude does not change toward them. The Doctor only pretends to change (mask) when dealing with Kino. He wears a mask of generosity to conceal his greedy scheme.