in this scene Kino, Juana and Coyotito are being introduced to the reader. They are inside their hut with just waking up.
In this scene Coyotito gets stung on the shoulder by a scorpion. And as a baby the poison in the scorpion could kill the baby.
They went to the doctors in the town and got denied services because they didn't have enough to pay. The servant lied and said he was "out" because the doctor didn't want to see them.
They decided to take Kino's canoe out on the water and go looking for oysters. As they were sailing The Sound of the Pearl began playing loudly in Kino's ears, he looked down saw a single oyster, dived in a grabbed it. There it was, a perfect pearl.
The news of the pearl spread like a wildfire. Soon the doctor knew about it and he was at their door.
The doctor offered his services for exchange of the money that Kino gets for the pearl. the doctor gives the baby a pill and he is on his way. Kino is not pleased that the treatment only involved a pill and the doctor refused the first time.