As the doctor approaches, why is Kino feeling rage?

Before discovering the pearl, Kino couldn't say anything to get the doctor to come and look at his son. The doctor refused to help people simply because they needed it..... he would not help without a guarantee of payment. After the pearl's discovery, the doctor was more then ready to help and immediately offers a cure. Kino is stuck...... believe what the doctor says is necessary or take the chance that his son will die.....

Kino felt the rage and hatred melting toward fear. He did not know, and perhaps this doctor did. And he could not take the chance of putting
his certain ignorance against this man's possible knowledge. He was trapped as his people were always trapped, and would be until, as he
had said, they could be sure that the things in the books were really in the books. He could not take a chance- not with the life or with the
straightness of Coyotito. He stood aside and let the doctor and his man enter the brush hut.