It’s almost better to think of the doctor as a symbol instead of a character. He’s so much a caricature of everything that’s wrong with colonial oppression that he isn’t exactly realistic. From the "little hammocks" of his eyes to his dressing gown of red watered Parisian silk, the doctor eats, sleeps, and breathes greed. With no respect for human life, he uses his profession only for money, even if that means manipulation. He tends to an old woman though her only ailment is only age, yet he refuses to treat Coyotito’s potentially fatal scorpion bite. His desire for wealth has completely skewed his sense of values.
But the lowest of all lows comes when the doctor visits the newly-rich Kino under pretense of treating his son. For a doctor to poison a patient intentionally is absurdly unethical – more evidence that this particular doctor is more a caricature than any sort of realistic depiction.
As if that were not enough, the Doctor is also incredibly racist. Before he refuses Kino on the grounds of his poverty, he is disgusted by the man’s race and remarks that he doesn’t treat Indians as he isn’t a veterinarian. Later, arriving at Kino’s house, the text reveals that the doctor thinks of "these people" as children. This is probably how he justifies treating Kino the way he does. By refusing to recognize Kino and Juana’s humanity, the doctor enables himself to treat them as children and as animals. That Kino is later forced to become animalistic in defense of himself and his family is one of the great tragedies of The Pearl.