How does Harper Lee portray and explore racial and class prejudice in Chapter 19 of To Kill A Mockingbird?

Tom Robinson's "crime" is explored in this chapter. Chapter 19 also explores the extent of racial polarization in Maycomb. Tom only enters Mayella's house because he feels sorry for her. Mayella is a lonely abused girl who craves attention, any kind of attention. Tom is a simple man and merely wants to help her "bust up a chifferobe". The unspoken crime is twofold. A black man stepping into a white girl's place is a strict social taboo. Atticus brings the other "crime" out into the open. Atticus says that Tom's only crime was to have the "unmitigated temerity to feel sorry for a white woman." Poor Tom, in an act of kindness, broke an ugly social law. Blacks can never be perceived in a position of strength over a white person.