When a grain of sand begins to irritate the oyster's inner folds of muscle, it emits a layer of secretion which surrounds the grain of sand and this emission, once started, continues until there is a great pearl.
Steinbeck then explains how a pearl is formed. The oyster bed where Kino dives is the same bed which once furnished enough pearls to make the king of Spain rich enough to become a great power in Europe. This should be remembered, for in the next chapter the doctor does administer something to Coyotito and it makes him very ill - until the doctor returns and gives him something else to counteract the first dose. Note that Steinbeck says that this primitive treatment was as good a remedy as any other, or probably better than any remedy that the doctor in town could give. Juana gathers some brown seaweed and makes a "flat damp poultice," which she applies to Coyotito's swollen shoulder. The irony here is, of course, that the canoe represents a continuation of the family tradition, since it belonged first to Kino's father and before that to his grandfather, and yet at the end of the story, Kino will have neither a child nor a canoe to pass on to another generation. Kino's canoe, which is "at once property and a source of food," has been in his family for two generations. This morning, they are far behind the others because of the attention required by Coyotito. Into this alien world come Kino and Juana. Along the shore, the graceful old canoes are silent, but the Gulf itself is teeming with sea life of various kinds: brown algae floats upward and supports little sea horses while poisonous fish lie "on the bottom in the eel-grass beds," and bright swimming crabs and many other varieties of sea life contend with each other in the battle of survival. In contrast to the first chapter, this chapter takes us out into the Gulf, where the Pearl of the World is to be found.