What does the fact that the jury took several hours to decide a verdict show about Maycomb's "usual disease

Usually when a jury takes a long time in deliberation, it means that there is at least some debate as to the guilt or innocence of the accused.  Perhaps Atticus’ emotional plea to the jury to do the right thing and that everyone should be treated equally in the court system had an effect.  However, Atticus is a realist.  He knows that an all white jury finding a black man innocent of unforced sex will never happen.  It does, however, show that Atticus did have some effect and that perhaps ideas about race are beginning to change in Maycomb.  Jem, in his innocence, is convinced that Atticus has won the case, and when the jury comes back with a guilty verdict, Jem is devastated.  It is then that Atticus tells Jem and Scout that his conscience forced him to at least try to defend Tom Robinson the best he could.  If not, Atticus wouldn’t have been able to live with himself.

the answer is somber