blood ill-temper'd This phrase could be interpreted as simply "bad humor," but Cassius means that his bad humor is not really his fault. According to the common thought of Shakespeare's time, health of body and mind depended on a balance of the four essential "humours" of the body—phlegm, yellow bile, black bile, and blood. When those humours get out of balance the person is "ill-tempered," unbalanced. (Our terms "bad humor," "good humor," "bad temper," and "temperamental" all derive from this conception of human psychology.) Thus Cassius is saying that his bad humor had a physical cause.