What is the remedy that the doctor gives the baby and then why is Kino suspicious about it?

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. The doctor's newfound interest in Kino stems from a manipulative and dangerous greed. His visit to Kino reveals that he not only wishes to secure part of Kino's new fortune through the salary the doctor might receive for treatment but, as shown by the doctor's attempt to locate the pearl in Kino's hut, that he intends to steal the pearl.