why does the doctor come to kino's house?

The doctor visits Kino's home, and although Kino tells him that Coyotito is nearly well, the doctor claims that the scorpion sting has a curious effect that comes later and if he is not treated he may suffer blindness or a withered leg. Not sure whether or not the doctor is telling the truth, Kino nevertheless lets him see the baby. The doctor takes a bottle of white powder and a gelatin capsule, and gives Coyotito a pill. The doctor tells them that the medicine may save the baby from pain, but he will come back in an hour to check on him. Kino is suspicious and hides the pearl.