The doctor does not care about Kino because he is poor, and he refuses to treat the sick baby.
Kino is suspicious of the doctor. Kino and his wife are aboriginals (Indians) and the doctor is one of the colonists, so he is a white man. The Indians never call a doctor, but when Coyotito gets bitten by a scorpion, Juana asks for the city doctor.
This doctor was not of his people. This doctor was of a race which for nearly four hundred years had beaten and starved and robbed and despised Kino's race, and frightened it too, so that the indigene came humbly to the door. (Ch. 1)
The doctor is not a kind person. Kino is right to be cautious. He seems to understand how the doctor thinks. The doctor looks down on them. He says that he is a doctor, not a veterinarian. Kino is already angry, and does not appreciate being called an animal.
The doctor takes no interest in Kino or his sick baby. Since he knows Kino can’t pay him, he dismisses him.
"Has he any money?" the doctor demanded. "No, they never have any money. I, I alone in the world am supposed to work for nothing- and I am tired of it. See if he has any money!" (Ch. 1)
He is right. Kino doesn't have any money. All Kino has are a few small misshapen seed pearls, so the doctor’s assistant sends him away with a lie that the doctor has gone out to see a serious case.
Kino was right about the doctor, so they are left to take care of their baby themselves. Juana does her best to help her baby herself, having already treated the wound when the incident first happened. It turns out that Juana does just as well as having a doctor. The baby starts to get better.