In "To Kill a Mockingbird," Maycomb's "usual disease" is racism and prejudice. Harper Lee uses Maycomb, a fictional town in Alabama, to illustrate the pervasive racism that existed in the American South during the 1930s. Atticus Finch, the moral compass of the novel, warns his children about the dangers of this "disease" and encourages them to challenge it.
In the novel, Scout Finch describes Maycomb as "a tired old town" where "nothing exciting ever happens." However, beneath the surface of the town lies a deep-seated racism that affects the lives of everyone in the community. The novel is set during the Great Depression, and many of the townspeople blame their economic struggles on the African American population.
One of the most vivid examples of the "usual disease" is the trial of Tom Robinson, a black man who is falsely accused of raping a white woman. Despite overwhelming evidence of Tom's innocence, the all-white jury finds him guilty because of their deeply ingrained racial prejudices. Atticus, who defends Tom, knows that he is fighting a losing battle but insists on doing the right thing anyway.
Another example is the way in which Maycomb's white citizens treat Boo Radley, a reclusive neighbor who is rumored to be mentally unstable. The children in the novel are fascinated by Boo and create elaborate stories about him. However, the adults in the town are quick to label Boo as a "crazy" and "dangerous" person without ever getting to know him. This attitude of fear and suspicion toward anyone who is different is another symptom of Maycomb's "usual disease."
Overall, Maycomb's "usual disease" is a pervasive and insidious form of racism that affects every aspect of the town's culture. Through her portrayal of Maycomb, Harper Lee shows how racism can be passed down from generation to generation and how difficult it is to eradicate once it has taken hold.