Act II?

In Act II, Brutus' wife Portia arrives and tells him he has left her bed and given her unkind looks. She begs him to tell her why he is so upset. He lies, telling her he is sick, to which she responds that it appears to be a sickness of the mind, not of the body. A strong woman of brave lineage, she again begs him to tell her what is wrong, asking him, "Think you I am no stronger than my sex, / Being so fathered and so husbanded?" (2.1.295-6). She then stabs herself in the thigh as proof of her courage. Brutus finally agrees to tell her what is concerning him, but sends her away before he is able to explain, because there is another knock on the door.

Portia struggles to convince Brutus that she is worthy of his confidence. She first kneels, begging him to share his secrets, and then stands up dramatically, stating, "Think you I am no stronger than my sex, / Being so fathered and so husbanded?" (2.1.295-6), and stabs herself in the thigh to prove her strength. Brutus capitulates to Portia, acknowledging her strength.

Gradesaver addresses the second portion of your question in detail in the analysis, simply follow the link below

http://www.gradesaver.com/julius-caesar/study-guide/section2/