Cussy’s scrubbing of her clothes suggests that she feels polluted in some way by her experience at the hospital. And, since Harriett has already compared her to an inkblot, the idea of stains is strongly associated with the discrimination that Cassie routinely suffers in her home. Doc’s experiments are a subtler version of Harriett’s hatred; both suggest that there’s something wrong with Cussy, and her desire to clean herself and her clothes shows how much she has unconsciously absorbed these messages. But she still finds strength and solace in doing things that help other people around her.