Just after Coyotito is stung, Juana tells Kino to get the doctor. Most of the people in the yard and at their door say the doctor will not come. This is the first obvious indication that Kino and Juana live in the poor section of town:
A wonderful thing, a memorable thing, to want the doctor. To get him would be a remarkable thing. The doctor never came to the cluster of brush houses. Why should he, when he had more than he could do to take care of the rich people who lived in the stone and plaster houses of the town.
As Kino, Juana, and other villagers approach the city, the border between poor and rich is represented by the line between the brush houses and the "city of stone and plaster." The beggars at the church noticed how faded Kino's and Juana's clothes looked and were able to conclude that they were poor.
The doctor represents a colonizing force. This colonization enforces the separation between rich and poor:
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.
Chapter 1 ends with the doctor refusing to see Coyotito because Kino and Juana have no money. However, when Kino finds the "Pearl of the World," the doctor immediately changes his tune and goes to treat the child. Pearl buyers and most everyone in town also become interested in Kino and his family because of the pearl. Juana's warning that the pearl is evil soon bears some truth and the implication is that wealth can easily corrupt a person (such as the doctor) or a situation (such as it did with Kino and Juana).